U.S. patent application number 12/539586 was filed with the patent office on 2010-04-08 for method of imaging coding pattern comprising columns and rows of coordinate data.
This patent application is currently assigned to Silverbrook Research Pty Ltd. Invention is credited to Paul Lapstun.
Application Number | 20100084468 12/539586 |
Document ID | / |
Family ID | 42072943 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100084468 |
Kind Code |
A1 |
Lapstun; Paul |
April 8, 2010 |
METHOD OF IMAGING CODING PATTERN COMPRISING COLUMNS AND ROWS OF
COORDINATE DATA
Abstract
A method of imaging a coding pattern disposed on a surface of a
substrate. The method comprises the steps of: (a) operatively
positioning an optical reader relative to the surface and capturing
an image of a portion of the coding pattern, said coding pattern
comprising: (b) sampling and decoding x-coordinate data and
y-coordinate data within the imaged portion; and (c) determining a
position of the reader. All the x-coordinate data is represented in
a column of an imaged tag and all the y-coordinate data is
represented in a row of the imaged tag. The column and the row each
have a width v. The imaged portion has a diameter of at least (l+v)
2 and less than (2l) 2.
Inventors: |
Lapstun; Paul; (Balmain,
AU) |
Correspondence
Address: |
SILVERBROOK RESEARCH PTY LTD
393 DARLING STREET
BALMAIN
2041
AU
|
Assignee: |
Silverbrook Research Pty
Ltd
|
Family ID: |
42072943 |
Appl. No.: |
12/539586 |
Filed: |
August 11, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61102299 |
Oct 2, 2008 |
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Current U.S.
Class: |
235/454 |
Current CPC
Class: |
G06K 7/10772 20130101;
G06K 7/1417 20130101; G06K 19/06037 20130101 |
Class at
Publication: |
235/454 |
International
Class: |
G06K 7/10 20060101
G06K007/10 |
Claims
1. A method of imaging a coding pattern disposed on a surface of a
substrate, said method comprising the steps of: (a) operatively
positioning an optical reader relative to said surface and
capturing an image of a portion of said coding pattern, said coding
pattern comprising: a plurality of contiguous square tags of length
l, each tag comprising x-coordinate data and y-coordinate data; and
a plurality of data elements contained in each tag, said
x-coordinate data being represented by a respective set of data
elements and said y-coordinate data being represented by a
respective set of data elements, wherein: all said x-coordinate
data is represented in a column of said tag parallel with a y-axis;
all said y-coordinate data is represented in a row of said tag
parallel with an x-axis; and said column and said row each have a
width v, (b) sampling and decoding x-coordinate data and
y-coordinate data within said imaged portion; and (c) determining a
position of said reader, wherein said imaged portion has a diameter
of at least (l+v) 2 and less than (21) V2.
2. The method of claim 1, wherein said coding pattern comprises: a
plurality of target elements defining a target grid, said target
grid comprising a plurality of cells, wherein neighboring cells
share target elements and wherein each tag is defined by a
plurality of contiguous cells.
3. The method of claim 2, wherein each tag comprises M.sup.2
contiguous square cells, wherein M is an integer having a value of
at least 1.
4. The method of claim 1, wherein said data elements are
macrodots.
5. The method of claim 1, wherein v=ts, wherein: s is defined as a
spacing between adjacent macrodots; t is an integer value of 2 or
more.
6. The method of claim 4, wherein said macrodots encode data values
by pulse position modulation (PPM).
7. The method of claim 6, wherein a portion of data is represented
by m macrodots, each of said macrodots occupying a respective
position from a plurality of predetermined possible positions p
within said cell, the respective positions of said macrodots
representing one of a plurality of possible data values.
8. The method of claim 7, wherein m is an integer of 1 or more, and
p>m.
9. The method of claim 7, wherein said portion of data is a
Reed-Solomon symbol.
10. The method of claim 9, wherein each cell defines a symbol
group, each symbol group comprising a plurality of said
Reed-Solomon symbols.
11. The method of claim 9, wherein said x-coordinate data is
encoded as an x-coordinate codeword comprised of a respective set
of said X-Reed-Solomon symbols, and said y-coordinate data is
encoded as a y-coordinate codeword comprised of a respective set of
said Y-Reed-Solomon symbols.
12. The method of claim 11, wherein said X-Reed-Solomon symbols are
configured and oriented in said column so as to have said width v,
and wherein said Y-Reed-Solomon symbols are configured and oriented
in said row so as to have said width v.
13. The method of claim 10, wherein each tag comprises a plurality
of common codewords, each common codeword being comprised of a
respective set of said Reed-Solomon symbols, wherein said plurality
of common codewords are defined as codewords common to a plurality
of contiguous tags, said method further comprising: sampling and
decoding said common codeword within said imaged portion.
14. The method of claim 13, wherein each symbol group comprises a
fragment of at least one of said common codewords, and contiguous
symbol groups are arranged such that any tag-sized portion of said
coding pattern is guaranteed to contain said plurality of common
codewords irrespective of whether a whole tag is contained in said
portion.
15. The method of claim 13, wherein said one or more of said common
codewords encode region identity data uniquely identifying a region
of said surface, said method further comprising: determining said
an identity of said region.
16. The method of claim 15, wherein said region identity data
uniquely identifies said substrate.
17. The method of claim 2, wherein each cell comprises a
registration symbol encoded by a respective set of said data
elements, said method further comprising sampling and decoding said
registration symbol to identifying one or more of: a translation of
said cell relative to a tag containing said cell; an orientation of
a layout of tag data with respect to said target grid; a number of
cells in each tag; a flag associated with said tag.
18. The method of claim 17, wherein each cell comprises a first and
second registration symbols, said first registration symbol
identifying a first orthogonal translation of said cell, said
second registration symbol identifying a second orthogonal
translation of said cell.
19. A system for imaging a coding pattern disposed on a surface of
a substrate, said system comprising: (A) said substrate, wherein
said coding pattern comprises: a plurality of contiguous square
tags of length l, each tag comprising x-coordinate data and
y-coordinate data; and a plurality of data elements contained in
each tag, said x-coordinate data being represented by a respective
set of data elements and said y-coordinate data being represented
by a respective set of data elements, wherein: all said
x-coordinate data is represented in a column of said tag parallel
with a y-axis; all said y-coordinate data is represented in a row
of said tag parallel with an x-axis; and said column and said row
each have a width v, (B) an optical reader comprising: an image
sensor for capturing an image of a portion of said coding pattern,
said image sensor having a field-of-view of at least (l+v) 2 and
less than (21) 2; and a processor configured for performing the
steps of: (i) sampling and decoding x-coordinate data and
y-coordinate data contained in an imaged portion; and (ii)
determining a position of said reader.
20. An optical reader for imaging a coding pattern disposed on a
surface of a substrate, said coding pattern comprising: a plurality
of contiguous square tags of length l, each tag comprising
x-coordinate data and y-coordinate data; and a plurality of data
elements contained in each tag, said x-coordinate data being
represented by a respective set of data elements and said
y-coordinate data being represented by a respective set of data
elements, wherein: all said x-coordinate data is represented in a
column of said tag parallel with a y-axis; all said y-coordinate
data is represented in a row of said tag parallel with an x-axis;
and said column and said row each have a width v, said optical
reader comprising: an image sensor for capturing an image of a
portion of said coding pattern, said image sensor having a
field-of-view of at least (l+v) 2 and less than (2l) 2; and a
processor configured for performing the steps of: (i) sampling and
decoding x-coordinate data and y-coordinate data contained in an
imaged portion; and (ii) determining a position of said reader.
Description
FIELD OF INVENTION
[0001] The present invention relates to a position-coding pattern
on a surface.
COPENDING APPLICATIONS
[0002] The following applications have been filed by the Applicant
simultaneously with the present application: [0003] NPT100US
NPT101US NPT102US
[0004] The disclosures of these co-pending applications are
incorporated herein by reference.
[0005] The above applications have been identified by their filing
docket number, which will be substituted with the corresponding
application number, once assigned.
CROSS REFERENCES
[0006] The following patents or patent applications filed by the
applicant or assignee of the present invention are hereby
incorporated by cross-reference.
TABLE-US-00001 10/815,621 10/815,635 10/815,647 11/488,162
10/815,636 11/041,652 11/041,609 11/041,556 10/815,609 7,204,941
7,278,727 10/913,380 7,122,076 7,156,289 09/575,197 6,720,985
7,295,839 09/722,174 7,068,382 7,094,910 7,062,651 6,644,642
6,549,935 6,987,573 6,727,996 6,760,119 7,064,851 6,290,349
6,428,155 6,785,016 6,831,682 6,741,871 6,965,439 10/932,044
6,870,966 6,474,888 6,724,374 6,788,982 7,263,270 6,788,293
6,737,591 09/693,514 10/778,056 10/778,061 11/193,482 7,055,739
6,830,196 7,182,247 7,082,562 10/409,864 7,108,192 10/492,169
10/492,152 10/492,168 10/492,161 7,308,148 6,957,768 7,170,499
11/856,061 11/672,522 11/672,950 11/754,310 12/015,507 7,148,345
12/025,746 12/025,762 12/025,765 10/407,212 6,902,255 6,755,509
12/178,611 12/178,619
BACKGROUND
[0007] The Applicant has previously described a method of enabling
users to access information from a computer system via a printed
substrate e.g. paper. The substrate has a coding pattern printed
thereon, which is read by an optical sensing device when the user
interacts with the substrate using the sensing device. A computer
receives interaction data from the sensing device and uses this
data to determine what action is being requested by the user. For
example, a user may make handwritten input onto a form or make a
selection gesture around a printed item. This input is interpreted
by the computer system with reference to a page description
corresponding to the printed substrate.
[0008] It would desirable to improve the coding pattern printed on
the substrate so as to maximize usage of images captured by the
sensing device. It would be further desirable to provide variants
of a position coding pattern, suitable for printing by different
types of printer, where each variant is readable by the same
optical reader.
SUMMARY OF INVENTION
[0009] In a first aspect, the present invention provides a
substrate having a first coding pattern disposed on a surface
thereof, the first coding pattern comprising: [0010] a plurality of
target elements defining a target grid, the target grid comprising
a plurality of cells, wherein neighboring cells share target
elements; [0011] a plurality of data elements contained in each
cell; and [0012] a plurality of tags, each tag being defined by a
first set of contiguous cells, each tag comprising respective tag
data encoded by a respective set of the data elements, wherein each
cell comprises one or more registration symbols encoded by a
respective set of the data elements, each of the one or more
registration symbols identifying the cell as being contained in the
first set and thereby contained in the first coding pattern.
[0013] The registration symbols advantageously provide a means by
which the first coding pattern can be distinguished from other
coding pattern(s) of the same general type.
[0014] Optionally, a number of cells contained in the first set
identifies the first set and thereby the first coding pattern.
Optionally, each of the registration symbols identifies the number
of cells contained in the first set. Optionally, each registration
symbol distinguishes the first coding pattern from a second coding
pattern. Advantageously, the registration symbols identify the
first coding pattern by identifying the number of cells contained
in each tag. For example, a first coding pattern have contain nine
cells per tag, whilst a second coding pattern may have four cells
per tag.
[0015] Optionally, the first coding pattern and the second coding
pattern are both readable and decodable by a same optical reader.
Hence, the Netpage pen can read and decode different Netpage
position-coding patterns, irrespective of the actual number of
cells per tag. This enables different position-coding patterns to
be used and printed, depending on the print capabilities of a
printer
[0016] Optionally, the second coding pattern comprises: [0017] a
plurality of target elements defining a target grid, the target
grid comprising a plurality of cells, wherein neighboring cells
share target elements; [0018] a plurality of data elements
contained in each cell; and [0019] a plurality of tags, each tag
being defined by a second set of contiguous cells, each tag
comprising respective tag data encoded by a respective set of the
data elements, wherein the second set contains a different number
of cells than the first set.
[0020] Hence, the second-position coding pattern is typically of
the same general type as the first position-coding pattern.
[0021] Optionally, each cell of the first coding pattern and the
second coding pattern comprises one or more registration symbols. A
large number of registration symbols in each tag provides a high
degree of redundancy, meaning that the pen can robustly recognize a
particular coding pattern.
[0022] Optionally, the registration symbols in the first and second
coding patterns are configured and positioned identically relative
to target elements contained by each cell. The relative positioning
of the registration symbols in both the first and second coding
patterns is the same, so that the pen can find the registrations
symbols before it identifies which coding pattern it is
reading.
[0023] Optionally, the second coding pattern is adapted to be
printed at a lower print resolution than the first coding pattern.
Optionally, the second set contains a fewer number of cells than
the first set.
[0024] Optionally, each registration symbol identifies a
translation of the cell relative to a tag containing the cell. This
enables alignment of the tag(s) with the target grid. Typically, a
first translation codeword (e.g. 0, 1, 2) is reserved for the first
coding pattern, whilst a second translation codeword (e.g. 3, 4) is
reserved for the second coding pattern.
[0025] Optionally, each cell comprises a pair of orthogonal
registration symbols, each orthogonal registration symbol
identifying a respective orthogonal translation of the cell
relative to a tag containing the cell. Hence, each registration
symbol is identifies either an x-translation or a y-translation of
a cell relative to a tag containing that cell.
[0026] Optionally, each tag is square and comprises M.sup.2
contiguous square cells, wherein M is an integer having a value of
at least 2. Typical tag sizes are M=2, 3 or 4. Preferably, M=2 or
3.
[0027] Optionally, M registration symbols in a row of M cells
define a cyclic position code having minimum distance M, the code
being defined by a first translation codeword.
[0028] Optionally, M registration symbols in a column of M cells
define a cyclic position code having minimum distance M, the code
being defined by a second translation codeword.
[0029] Optionally, each tag comprises N cells, and at least N
registration symbols form a third translation codeword with minimum
distance N, wherein N is an integer having a value of at least
4.
[0030] Advantageously, the first, second and/or third translation
codewords enable robust alignment of the tag(s) with the target.
For example, in a tag containing nine cells, four symbol errors in
the third translation codeword may be corrected.
[0031] Optionally, each registration symbol further identifies an
orientation of a layout of the tag data with respect to the target
grid. The encoded orientation enables the Netpage pen to determine
its orientation (yaw) relative to the tag data, and hence relative
to the substrate.
[0032] Typically, the data elements are macrodots (i.e. readable
marks in the form of dots). Typically, a portion of data is
represented by m macrodots, each of the macrodots occupying a
respective position from a plurality of predetermined possible
positions p within the cell, the respective positions of the
macrodots representing one of a plurality of possible data values,
wherein m is an integer of 1 or more (usually 2 or more), and
p>m (typically p.gtoreq.2m). Encoding by multi-PPM in this way
ensures uniform coverage of the substrate with macrodots, which
helps to reduce visibility. Moreover, PPM encoding provides an
internal luminescence reference for reading macrodots. For example,
the darkest m macrodots in the p positions are taken to be the PPM
data, without the need to refer to any external luminescence
threshold value.
[0033] Optionally, each cell defines a symbol group, each symbol
group comprising a plurality of Reed-Solomon symbols encoded by a
plurality of the data elements.
[0034] Optionally, at least some of said tag data is encoded as a
local codeword comprised of a set of the Reed-Solomon symbols. The
local tag data typically identifies a location of the tag.
[0035] In a second aspect, there is provided a method of imaging
either a first coding pattern or a second coding pattern disposed
on a surface, the method comprising the steps of:
[0036] (a) operatively positioning an optical reader relative to
the surface having either the first or second coding pattern
disposed thereon;
[0037] (b) capturing an image of a portion of the first or second
coding pattern, the first and second coding patterns each
comprising: [0038] a plurality of target elements defining a target
grid, the target grid comprising a plurality of cells, wherein
neighboring cells share target elements; [0039] a plurality of data
elements contained in each cell; and [0040] a plurality of tags,
each tag being defined by a set of contiguous cells, each tag
comprising respective tag data encoded by a respective set of the
data elements, wherein each cell comprises one or more registration
symbols encoded by a respective set of the data elements;
[0041] (c) sampling and decoding at least one registration symbol
contained in the imaged portion;
[0042] (d) determining, from the decoded registration symbol, an
identifier of the first or second coding pattern, the identifier
indicating a number of cells contained in each tag;
[0043] (e) determining, from the identifier, whether the optical
reader is positioned relative to the first coding pattern or the
second coding pattern; and
[0044] (f) using the indicated number of cells to sample and decode
the tag data, wherein a number of cells contained in each tag of
the first coding pattern is different from a number of cells
contained in each tag of the second coding pattern.
[0045] Optionally, each registration symbol identifies a
translation of the cell relative to a tag containing the cell, the
method further comprising the step of:
[0046] using the translation to sample and decode the tag data.
[0047] Optionally, each registration symbol identifies an
orientation of a layout of the tag data with respect to the target
grid, the method further comprising the step of:
[0048] using the orientation to sample and decode the tag data.
[0049] In a third aspect, there is provided a system for imaging
either a first coding pattern or a second coding pattern, the
system comprising:
(A) a substrate having either the first coding pattern or the
second coding pattern disposed on a surface thereof, wherein the
first and second coding patterns each comprises:
[0050] a plurality of target elements defining a target grid, the
target grid comprising a plurality of cells, wherein neighboring
cells share target elements;
[0051] a plurality of data elements contained in each cell; and
[0052] a plurality of tags, each tag being defined by a set of
contiguous cells, each tag comprising respective tag data encoded
by a respective set of the data elements, wherein each cell
comprises one or more registration symbols encoded by a respective
set of the data elements;
(B) an optical reader comprising:
[0053] an image sensor for capturing an image of a portion of the
first or second coding pattern; and
[0054] a processor configured for performing the steps of: [0055]
(i) sampling and decoding at least one registration symbol
contained in the imaged portion; [0056] (ii) determining, from the
decoded registration symbol, an identifier of the first or second
coding pattern, the identifier indicating a number of cells
contained in each tag; [0057] (iii) determining, from the
identifier, whether the optical reader is positioned relative to
the first coding pattern or the second coding pattern; and [0058]
(iv) using the indicated number of cells to sample and decode the
tag data, wherein a number of cells contained in each tag of the
first coding pattern is different from a number of cells contained
in each tag of the second coding pattern.
[0059] Optionally, each registration symbol identifies a
translation of the cell relative to a tag containing the cell, the
processor being configured to perform the further step of:
[0060] using the translation to sample and decode the tag data.
[0061] Optionally, each registration symbol identifies an
orientation of a layout of the tag data with respect to the target
grid, the processor being configure to perform the further step
of:
[0062] using the orientation to sample and decode the tag data.
[0063] In a fourth aspect, there is provided an optical reader for
imaging either a first coding pattern or a second coding pattern,
the first and second coding patterns each comprising:
[0064] a plurality of target elements defining a target grid, the
target grid comprising a plurality of cells, wherein neighboring
cells share target elements;
[0065] a plurality of data elements contained in each cell; and
[0066] a plurality of tags, each tag being defined by a set of
contiguous cells, each tag comprising respective tag data encoded
by a respective set of the data elements, wherein each cell
comprises one or more registration symbols encoded by a respective
set of the data elements; the optical reader comprising:
[0067] an image sensor for capturing an image of a portion of
either first or second coding pattern; and
[0068] a processor configured for performing the steps of: [0069]
(i) sampling and decoding at least one registration symbol
contained in the imaged portion; [0070] (ii) determining, from the
decoded registration symbol, an identifier of the first or second
coding pattern, the identifier indicating a number of cells
contained in each tag; [0071] (iii) determining, from the
identifier, whether the optical reader is positioned relative to
the first coding pattern or the second coding pattern; and [0072]
(iv) using the indicated number of cells to sample and decode the
tag data, wherein a number of cells contained in each tag of the
first coding pattern is different from a number of cells contained
in each tag of the second coding pattern.
[0073] It will be appreciated that optional embodiments of the
first aspect may also be optional embodiments of the second, third
or fourth aspects.
[0074] In a fifth aspect, there is provided a substrate having a
coding pattern disposed on a surface thereof, the coding pattern
comprising:
[0075] a plurality of contiguous square tags of length l, each tag
comprising x-coordinate data and y-coordinate data; and
[0076] a plurality of data elements contained in each tag, the
x-coordinate data being represented by a respective set of data
elements and the y-coordinate data being represented by a
respective set of data elements,
wherein:
[0077] all the x-coordinate data is represented in a column of the
tag parallel with a y-axis;
[0078] all the y-coordinate data is represented in a row of the tag
parallel with an x-axis; and the column and the row each have a
width v, such that any square portion of the coding pattern having
a length (I+v) is guaranteed to contain the x-coordinate data and
the y-coordinate data for a tag irrespective of whether a whole tag
is contained in the portion.
[0079] The fifth aspect of the invention advantageously enables
non-replication of coordinate data in each tag, which saves on tag
space. Typically, x-coordinate data should be replicated in each
vertical half of tag, and y-coordinate data should be replicated in
each horizontal half of a tag. However, by encoding all
x-coordinate data in one column, and all y-coordinate data in one
row, the requirement for replication is obviated. If the column or
row has a width v, then any square portion of length (l+v) is
guaranteed to contain the relevant coordinate data. Moreover, if
the width v corresponds to a width or length of a coordinate data
symbol (depending on the shape and orientation of coordinate data
symbols in the column or row), then it is ensured that any square
portion of length (l+v) is guaranteed to contain the relevant
coordinate data from spatially coherent samples i.e. from the same
symbol, as opposed to partial symbols at opposite sides of a field
of view.
[0080] Optionally, a plurality of target elements define a target
grid, the target grid comprising a plurality of cells, wherein
neighboring cells share target elements and wherein each tag is
defined by a plurality of contiguous cells.
[0081] Optionally, each tag comprises M.sup.2 contiguous square
cells, wherein M is an integer having a value of at least 1.
Typical tag sizes are M=2, 3 or 4. Preferably, M=2 or 3
[0082] Optionally, the data elements are macrodots, which are
readable dot-like marks formed by a plurality of contiguous printed
dots.
[0083] Optionally, v=ts, wherein: s is defined as a spacing between
adjacent macrodots; and t is an integer value of 2 or more.
[0084] Optionally, the macrodots encode data values by pulse
position modulation (PPM).
[0085] Optionally, a portion of data is represented by m macrodots,
each of the macrodots occupying a respective position from a
plurality of predetermined possible positions p within the cell,
the respective positions of the macrodots representing one of a
plurality of possible data values.
[0086] Optionally, the x-coordinate data is encoded as an
x-coordinate codeword comprised of a respective set of the
X-Reed-Solomon symbols, and the y-coordinate data is encoded as a
y-coordinate codeword comprised of a respective set of the
Y-Reed-Solomon symbols.
[0087] Optionally, the X-Reed-Solomon symbols are configured and
oriented in the column so as to have the width v, and wherein the
Y-Reed-Solomon symbols are configured and oriented in the row so as
to have the width v.
[0088] Optionally, each tag comprises a plurality of common
codewords, each common codeword being comprised of a respective set
of the Reed-Solomon symbols, wherein the plurality of common
codewords are defined as codewords common to a plurality of
contiguous tags. A common codeword typically encodes a region ID or
page ID for the substrate.
[0089] Optionally, each symbol group comprises a fragment of at
least one of the common codewords, and contiguous symbol groups are
arranged such that any tag-sized portion of the coding pattern is
guaranteed to contain the plurality of common codewords
irrespective of whether a whole tag is contained in the
portion.
[0090] Optionally, each cell comprises a registration symbol
encoded by a respective set of the data elements, the registration
symbol identifying one or more of:
[0091] a translation of the cell relative to a tag containing the
cell;
[0092] an orientation of a layout of tag data with respect to the
target grid;
[0093] a number of cells in each tag;
[0094] a flag associated with the tag.
[0095] Optionally, each cell comprises first and second
registration symbols, the first registration symbol identifying a
first orthogonal translation of the cell, the second registration
symbol identifying a second orthogonal translation of the cell.
[0096] Optionally, the first registration symbol identifies a first
direction component of the orientation, and the second registration
symbol identifies a second direction component of the orientation,
such that the first and second orthogonal registration symbols
together identify the orientation via the first and second
direction components.
[0097] Optionally, the target elements are target dots and the data
elements are macrodots, and each target dot has a diameter of at
least twice that of each macrodot. This enables low-pass filtration
of captured images to retain target elements but obscure
macrodots.
[0098] In a sixth aspect, there is provided a method of imaging a
coding pattern disposed on a surface of a substrate, the method
comprising the steps of:
[0099] (a) operatively positioning an optical reader relative to
the surface and capturing an image of a portion of the coding
pattern, the coding pattern comprising:
[0100] a plurality of contiguous square tags of length l, each tag
comprising x-coordinate data and y-coordinate data; and
[0101] a plurality of data elements contained in each tag, the
x-coordinate data being represented by a respective set of data
elements and the y-coordinate data being represented by a
respective set of data elements,
wherein:
[0102] all the x-coordinate data is represented in a column of the
tag parallel with a y-axis;
[0103] all the y-coordinate data is represented in a row of the tag
parallel with an x-axis; and
[0104] the column and the row each have a width v,
[0105] (b) sampling and decoding x-coordinate data and y-coordinate
data within the imaged portion; and
[0106] (c) determining a position of the reader,
wherein the imaged portion has a diameter of at least (l+v) 2 and
less than (2) 2.
[0107] Since the field of view of the optical reader is not
required to have a diameter of at least two tag diameters, then the
imaging requirements of the reader are reduced. Hence, the
position-coding pattern not only provides efficient use of tag
space, but also allows the imaging field of view of the tag reader
to be minimized.
[0108] Optionally, each tag comprises a plurality of common
codewords, each common codeword being comprised of a respective set
of the Reed-Solomon symbols, wherein the plurality of common
codewords are defined as codewords common to a plurality of
contiguous tags, the method further comprising the step of:
[0109] sampling and decoding the common codeword within the imaged
portion.
[0110] Optionally, one or more of the common codewords encode
region identity data uniquely identifying a region of the surface,
the method further comprising:
[0111] determining the an identity of the region.
[0112] Optionally, the region identity data uniquely identifies the
substrate.
[0113] In a seventh aspect, there is provided a system for imaging
a coding pattern disposed on a surface of a substrate, the system
comprising:
(A) the substrate, wherein the coding pattern comprises:
[0114] a plurality of contiguous square tags of length l, each tag
comprising x-coordinate data and y-coordinate data; and
[0115] a plurality of data elements contained in each tag, the
x-coordinate data being represented by a respective set of data
elements and the y-coordinate data being represented by a
respective set of data elements,
wherein:
[0116] all the x-coordinate data is represented in a column of the
tag parallel with a y-axis;
[0117] all the y-coordinate data is represented in a row of the tag
parallel with an x-axis; and
[0118] the column and the row each have a width v,
(B) an optical reader comprising:
[0119] an image sensor for capturing an image of a portion of the
coding pattern, the image sensor having a field-of-view of at least
(l+v) 2 and less than (2l) 2; and
[0120] a processor configured for performing the steps of: [0121]
(i) sampling and decoding x-coordinate data and y-coordinate data
contained in an imaged portion; and [0122] (ii) determining a
position of the reader.
[0123] In an eighth aspect, there is provided an optical reader for
imaging a coding pattern disposed on a surface of a substrate, the
coding pattern comprising:
[0124] a plurality of contiguous square tags of length l, each tag
comprising x-coordinate data and y-coordinate data; and
[0125] a plurality of data elements contained in each tag, the
x-coordinate data being represented by a respective set of data
elements and the y-coordinate data being represented by a
respective set of data elements,
wherein:
[0126] all the x-coordinate data is represented in a column of the
tag parallel with a y-axis;
[0127] all the y-coordinate data is represented in a row of the tag
parallel with an x-axis; and
[0128] the column and the row each have a width v, the optical
reader comprising:
[0129] an image sensor for capturing an image of a portion of the
coding pattern, the image sensor having a field-of-view of at least
(l+v) 2 and less than (2) 2; and
[0130] a processor configured for performing the steps of: [0131]
(i) sampling and decoding x-coordinate data and y-coordinate data
contained in an imaged portion; and [0132] (ii) determining a
position of the reader.
[0133] It will be appreciated that optional embodiments of the
fifth aspect may also be optional embodiments of sixth, seventh and
eighth aspects.
BRIEF DESCRIPTION OF DRAWINGS
[0134] Preferred and other embodiments of the invention will now be
described, by way of non-limiting example only, with reference to
the accompanying drawings, in which:
[0135] FIG. 1 is a schematic of a relationship between a sample
printed netpage and its online page description;
[0136] FIG. 2 shows an embodiment of basic netpage architecture
with various alternatives for the relay device;
[0137] FIG. 3 shows the structure of a tag for a first
position-coding pattern;
[0138] FIG. 4 shows a group of twelve data symbols and four targets
for the first position-coding pattern;
[0139] FIG. 5 shows the layout of a 2-6PPM and 3-6PPM data symbol
for the first position-coding pattern;
[0140] FIG. 6 shows the spacing of macrodot positions in the first
position-coding pattern;
[0141] FIG. 7 shows the layout of a 2-6PPM registration symbol for
the first position-coding pattern;
[0142] FIG. 8 shows a semi-replicated x-coordinate codeword X for
the first position-coding pattern;
[0143] FIG. 9 shows a semi-replicated y-coordinate codeword Y for
the first position-coding pattern;
[0144] FIG. 10 shows common codewords A, B, C and D, with codeword
A shown in bold outline for the first position-coding pattern;
[0145] FIG. 11 shows an optional codeword E for the first
position-coding pattern;
[0146] FIG. 12 shows the layout of a complete tag for the first
position-coding pattern;
[0147] FIG. 13 shows the layout of a Reed-Solomon codeword for the
first position-coding pattern;
[0148] FIG. 14 shows the structure of a tag for a second
position-coding pattern;
[0149] FIG. 15 shows a group of eight data symbols and four targets
for the second position-coding pattern;
[0150] FIG. 16 shows the layout of a 2-9PPM data symbol for the
second position-coding pattern;
[0151] FIG. 17 shows an x-coordinate codeword X for the second
position-coding pattern;
[0152] FIG. 18 shows a y-coordinate codeword Y for the second
position-coding pattern;
[0153] FIG. 19 shows a common codeword A for the second
position-coding pattern;
[0154] FIG. 20 shows the layout of a complete tag for the second
position-coding pattern;
[0155] FIG. 21 shows the layout of a Reed-Solomon codeword for the
second position-coding pattern;
[0156] FIG. 22 is a flowchart of initial image processing by the
Netpage pen;
[0157] FIG. 23 is a flowchart of codeword decoding subsequent to
the initial image processing;
[0158] FIG. 24 shows a nib and elevation of the Netpage pen held by
a user;
[0159] FIG. 25 shows the pen held by a user at a typical incline to
a writing surface;
[0160] FIG. 26 is a lateral cross section through the pen;
[0161] FIG. 27A is a bottom and nib end partial perspective of the
pen;
[0162] FIG. 27B is a bottom and nib end partial perspective with
the fields of illumination and field of view of the sensor window
shown in dotted outline;
[0163] FIG. 28 is a longitudinal cross section of the pen;
[0164] FIG. 29A is a partial longitudinal cross section of the nib
and barrel molding;
[0165] FIG. 29B is a partial longitudinal cross section of the IR
LED's and the barrel molding;
[0166] FIG. 30 is a ray trace of the pen optics adjacent a sketch
of the ink cartridge;
[0167] FIG. 31 is a side elevation of the lens;
[0168] FIG. 32 is a side elevation of the nib and the field of view
of the optical sensor; and
[0169] FIG. 33 is a block diagram of the pen electronics.
DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS
1.1 Netpage System Architecture
[0170] In a preferred embodiment, the invention is configured to
work with the netpage networked computer system, an overview of
which follows. In brief summary, the preferred form of the netpage
system employs a computer interface in the form of a mapped
surface, that is, a physical surface which contains references to a
map of the surface maintained in a computer system. The map
references can be queried by an appropriate sensing device.
Depending upon the specific implementation, the map references may
be encoded visibly or invisibly, and defined in such a way that a
local query on the mapped surface yields an unambiguous map
reference both within the map and among different maps. The
computer system can contain information about features on the
mapped surface, and such information can be retrieved based on map
references supplied by a sensing device used with the mapped
surface. The information thus retrieved can take the form of
actions which are initiated by the computer system on behalf of the
operator in response to the operator's interaction with the surface
features.
[0171] In its preferred form, the netpage system relies on the
production of, and human interaction with, netpages. These are
pages of text, graphics and images printed on ordinary paper, but
which work like interactive webpages. Information is encoded on
each page using ink which is substantially invisible to the unaided
human eye. The ink, however, and thereby the coded data, can be
sensed by an optically imaging sensing device (or reader) and
transmitted to the netpage system. The sensing device may take the
form of a clicker (for clicking on a specific position on a
surface), a pointer having a stylus (for pointing or gesturing on a
surface using pointer strokes), or a pen having a marking nib (for
marking a surface with ink when pointing, gesturing or writing on
the surface). References herein to "pen" or "netpage pen" are
provided by way of example only. It will, of course, be appreciated
that the pen may take the form of any of the sensing devices or
readers described herein.
[0172] In one embodiment, active buttons and hyperlinks on each
page can be clicked with the sensing device to request information
from the network or to signal preferences to a network server. In
one embodiment, text written by hand on a netpage is automatically
recognized and converted to computer text in the netpage system,
allowing forms to be filled in. In other embodiments, signatures
recorded on a netpage are automatically verified, allowing
e-commerce transactions to be securely authorized. In other
embodiments, text on a netpage may be clicked or gestured to
initiate a search based on keywords indicated by the user.
[0173] As illustrated in FIG. 1, a printed netpage 1 can represent
a interactive form which can be filled in by the user both
physically, on the printed page, and "electronically", via
communication between the pen and the netpage system. The example
shows a "Request" form containing name and address fields and a
submit button. The netpage 1 consists of graphic data 2, printed
using visible ink, and a surface coding pattern 3 superimposed with
the graphic data. The surface coding pattern 3 comprises a
collection of tags 4. A typical tag 4 is shown in the shaded region
of FIG. 1, although it will be appreciated that contiguous tags 4,
defined by the coding pattern 3, are densely tiled over the whole
netpage 1.
[0174] The corresponding page description 5, stored on the netpage
network, describes the individual elements of the netpage. In
particular it describes the type and spatial extent (zone) of each
interactive element (i.e. text field or button in the example), to
allow the netpage system to correctly interpret input via the
netpage. The submit button 6, for example, has a zone 7 which
corresponds to the spatial extent of the corresponding graphic
8.
[0175] As illustrated in FIG. 2, a netpage sensing device 400, such
as the pen described in Section 5, works in conjunction with a
netpage relay device 601, which is an Internet-connected device for
home, office or mobile use. The pen 400 is wireless and
communicates securely with the netpage relay device 601 via a
short-range radio link 9. In an alternative embodiment, the netpage
pen 400 utilises a wired connection, such as a USB or other serial
connection, to the relay device 601.
[0176] The relay device 601 performs the basic function of relaying
interaction data to a page server 10, which interprets the
interaction data. As shown in FIG. 2, the relay device 601 may, for
example, take the form of a personal computer 601a, a netpage
printer 601b or some other relay 601c (e.g. personal computer or
mobile phone incorporating a web browser).
[0177] The netpage printer 601b is able to deliver, periodically or
on demand, personalized newspapers, magazines, catalogs, brochures
and other publications, all printed at high quality as interactive
netpages. Unlike a personal computer, the netpage printer is an
appliance which can be, for example, wall-mounted adjacent to an
area where the morning news is first consumed, such as in a user's
kitchen, near a breakfast table, or near the household's point of
departure for the day. It also comes in tabletop, desktop, portable
and miniature versions. Netpages printed on-demand at their point
of consumption combine the ease-of-use of paper with the timeliness
and interactivity of an interactive medium.
[0178] Alternatively, the netpage relay device 601 may be a
portable device, such as a mobile phone or PDA, a laptop or desktop
computer, or an information appliance connected to a shared
display, such as a TV. If the relay device 601 is not a netpage
printer 601b which prints netpages digitally and on demand, the
netpages may be printed by traditional analog printing presses,
using such techniques as offset lithography, flexography, screen
printing, relief printing and rotogravure, as well as by digital
printing presses, using techniques such as drop-on-demand inkjet,
continuous inkjet, dye transfer, and laser printing.
[0179] As shown in FIG. 2, the netpage sensing device 400 interacts
with a portion of the tag pattern on a printed netpage 1, or other
printed substrate such as a label of a product item 251, and
communicates, via a short-range radio link 9, the interaction to
the relay device 601. The relay 601 sends corresponding interaction
data to the relevant netpage page server 10 for interpretation. Raw
data received from the sensing device 400 may be relayed directly
to the page server 10 as interaction data. Alternatively, the
interaction data may be encoded in the form of an interaction URI
and transmitted to the page server 10 via a user's web browser
601c. The web browser 601c may then receive a URI from the page
server 10 and access a webpage via a webserver 201. In some
circumstances, the page server 10 may access application computer
software running on a netpage application server 13.
[0180] The netpage relay device 601 can be configured to support
any number of sensing devices, and a sensing device can work with
any number of netpage relays. In the preferred implementation, each
netpage sensing device 400 has a unique identifier. This allows
each user to maintain a distinct profile with respect to a netpage
page server 10 or application server 13.
[0181] Digital, on-demand delivery of netpages 1 may be performed
by the netpage printer 601b, which exploits the growing
availability of broadband Internet access. Netpage publication
servers 14 on the netpage network are configured to deliver
print-quality publications to netpage printers. Periodical
publications are delivered automatically to subscribing netpage
printers via pointcasting and multicasting Internet protocols.
Personalized publications are filtered and formatted according to
individual user profiles.
[0182] A netpage pen may be registered with a netpage registration
server 11 and linked to one or more payment card accounts. This
allows e-commerce payments to be securely authorized using the
netpage pen. The netpage registration server compares the signature
captured by the netpage pen with a previously registered signature,
allowing it to authenticate the user's identity to an e-commerce
server. Other biometrics can also be used to verify identity. One
version of the netpage pen includes fingerprint scanning, verified
in a similar way by the netpage registration server.
1.2 Netpages
[0183] Netpages are the foundation on which a netpage network is
built. They provide a paper-based user interface to published
information and interactive services.
[0184] As shown in FIG. 1, a netpage consists of a printed page (or
other surface region) invisibly tagged with references to an online
description 5 of the page. The online page description 5 is
maintained persistently by the netpage page server 10. The page
description describes the visible layout and content of the page,
including text, graphics and images. It also describes the input
elements on the page, including buttons, hyperlinks, and input
fields. A netpage allows markings made with a netpage pen on its
surface to be simultaneously captured and processed by the netpage
system.
[0185] Multiple netpages (for example, those printed by analog
printing presses) can share the same page description. However, to
allow input through otherwise identical pages to be distinguished,
each netpage may be assigned a unique page identifier. This page ID
(or, more generally, region ID) has sufficient precision to
distinguish between a very large number of netpages.
[0186] Each reference to the page description 5 is repeatedly
encoded in the netpage pattern. Each tag (and/or a collection of
contiguous tags) identifies the unique page on which it appears,
and thereby indirectly identifies the page description 5. Each tag
also identifies its own position on the page. Characteristics of
the tags are described in more detail below.
[0187] Tags are typically printed in infrared-absorptive ink on any
substrate which is infrared-reflective, such as ordinary paper, or
in infrared fluorescing ink. Near-infrared wavelengths are
invisible to the human eye but are easily sensed by a solid-state
image sensor with an appropriate filter.
[0188] A tag is sensed by a 2D area image sensor in the netpage
sensing device, and the tag data is transmitted to the netpage
system via the nearest netpage relay device 601. The pen 400 is
wireless and communicates with the netpage relay device 601 via a
short-range radio link. It is important that the pen recognize the
page ID and position on every interaction with the page, since the
interaction is stateless. Tags are error-correctably encoded to
make them partially tolerant to surface damage.
[0189] The netpage page server 10 maintains a unique page instance
for each unique printed netpage, allowing it to maintain a distinct
set of user-supplied values for input fields in the page
description 5 for each printed netpage 1.
2 NETPAGE TAGS
2.1 Tag Data Content
[0190] Each tag 4 identifies an absolute location of that tag
within a region of a substrate.
[0191] Each interaction with a netpage should also provide a region
identity together with the tag location. In a preferred embodiment,
the region to which a tag refers coincides with an entire page, and
the region ID is therefore synonymous with the page ID of the page
on which the tag appears. In other embodiments, the region to which
a tag refers can be an arbitrary subregion of a page or other
surface. For example, it can coincide with the zone of an
interactive element, in which case the region ID can directly
identify the interactive element.
[0192] As described in the Applicant's previous applications (e.g.
U.S. Pat. No. 6,832,717), the region identity may be encoded
discretely in each tag 4. As will be described in more detail
below, the region identity may be encoded by a plurality of
contiguous tags in such a way that every interaction with the
substrate still identifies the region identity, even if a whole tag
is not in the field of view of the sensing device.
[0193] Each tag 4 should preferably identify an orientation of the
tag relative to the substrate on which the tag is printed.
Orientation data read from a tag enables the rotation (yaw) of the
pen 400 relative to the substrate to be determined
[0194] A tag 4 may also encode one or more flags which relate to
the region as a whole or to an individual tag. One or more flag
bits may, for example, signal a sensing device to provide feedback
indicative of a function associated with the immediate area of the
tag, without the sensing device having to refer to a description of
the region. A netpage pen may, for example, illuminate an "active
area" LED when in the zone of a hyperlink.
[0195] A tag 4 may also encode a digital signature or a fragment
thereof. Tags encoding (partial) digital signatures are useful in
applications where it is required to verify a product's
authenticity. Such applications are described in, for example, US
Publication No. 2007/0108285, the contents of which is herein
incorporated by reference. The digital signature may be encoded in
such a way that it can be retrieved from every interaction with the
substrate. Alternatively, the digital signature may be encoded in
such a way that it can be assembled from a random or partial scan
of the substrate.
[0196] It will, of course, be appreciated that other types of
information (e.g. tag size etc) may also be encoded into each tag
or a plurality of tags, as will be explained in more detail
below.
2.2 Position-Coding Pattern Variants
[0197] Although the adoption of a ubiquitous position-coding
Netpage tag pattern for all users and all applications of the
Netpage system is desirable, there may be technological or other
barriers to such a ubiquitous coding pattern, at least during
initial uptake of the Netpage system. One such barrier is a print
resolution at which the position-coding pattern is printed. The
Netpage tag pattern is advantageously designed to be printed using
the Applicant's high-resolution (1600 dpi) pagewidth inkjet
printers. The Netpage system complements the Applicant's inkjet
printers, which are able to print Netpages having a high degree of
functionality and position resolution via the printed tags 4.
Ideally, Netpages are printed using `Netpage-aware` printers, which
are specifically tailored for printing Netpages.
[0198] However, the Netpage system is a generic page-based system
that need not be inextricably tied to such printers. Preferably,
Netpages should be printable using other types of printers,
including existing lower resolution (e.g. 300 dpi) print-on-demand
printers, such as laser printers and other inkjet printers.
Netpages should also be printable using traditional analogue
printing presses, which use, for example, established offset,
rotogravure or photogravure printing techniques.
[0199] Self-evidently, position-coding patterns designed to be
printed with high-resolution printers may not be printable using
lower resolution printing technologies. If a dot spacing in the
coding pattern is too small, then individual dots may not be
resolvable by a relatively low resolution printing technology.
Moreover, the resultant coding pattern, printed by a low-resolution
printer, would not be readable by the Netpage pen 400 if adjacent
dots are merged together.
[0200] One approach to this problem would be to provide a
ubiquitous Netpage coding pattern, which is suitable for printing
by both low-resolution and high-resolution printers. However, this
is an unsatisfactory solution to the problem, because the higher
degree of functionality and resolution of Netpages printed by the
Applicant's pagewidth inkjet printers would be lost
unnecessarily.
[0201] The present invention therefore provides two variants of the
Netpage position-coding pattern, both of which are readable by the
same Netpage pen 400. A first position-coding pattern (dubbed
"Yarrow" by the present Applicant) is suitable for printing by the
Applicant's high-resolution (1600 dpi) pagewidth inkjet printers
and has a high degree of functionality and resolution. A second
position-coding pattern (dubbed "Saffron" by the present Applicant)
is suitable for printing by relatively low resolution (e.g. 300
dpi) printers and has a lower degree of functionality and
resolution.
[0202] Importantly, both the first and second position-coding
patterns are readable by the Netpage pen 400 by virtue of features
common to each pattern. The Netpage pen 400 is able to determine
whether it is reading the first or second position-coding pattern
by decoding a registration symbol in each tag 4, as will be
explained in more detail below. Once the pen 400 has recognized the
coding pattern it is reading, decoding of tag data can proceed in
accordance with that particular coding pattern.
3 First Position--Coding Pattern ("Yarrow")
3.1 Background
[0203] An earlier version of the first position-coding pattern
("Yarrow") was described in Applicant's U.S. application Ser. Nos.
12/178,611 and 12/178,619 (Attorney Docket Nos. NPT087US and
NPT092US). This earlier version of the first position-coding
pattern has been modified for compatibility with the second
position-coding pattern described herein in Section 4. In
particular, the registration symbols now map to translation code
symbol values specifically identifying the first position-coding
pattern, as described in more detail in Section 3.6.1. The complete
first position-coding pattern will now be described in detail
below.
3.2 General Tag Structure
[0204] As described above in connection with FIG. 1, the netpage
surface coding generally consists of a dense planar tiling of tags.
In the first position-coding pattern ("Yarrow"), each tag 4 is
represented by two kinds of elements. Referring to FIGS. 3 and 4,
the first kind of element is a target element. Target elements in
the form of target dots 301 allow a tag 4 to be located in an image
of a coded surface, and allow the perspective distortion of the tag
to be inferred. The second kind of element is a data element in the
form of a macrodot 302 (see FIG. 6). The macrodots 302 encode data
values. As described in the Applicant's earlier disclosures (e.g.
U.S. Pat. No. 6,832,717), the presence or absence of a macrodot was
be used to represent a binary bit. However, the tag structure of
the first position-coding pattern encodes a data value using
multi-pulse position modulation, which is described in more detail
in Section 3.3.
[0205] The coding pattern 3 is represented on the surface in such a
way as to allow it to be acquired by an optical imaging system, and
in particular by an optical system with a narrowband response in
the near-infrared. The pattern 3 is typically printed onto the
surface using a narrowband near-infrared ink.
[0206] FIG. 3 shows the structure of a complete tag 4A from the
first position-coding pattern, with target elements 301 shown. The
tag 4A is square and contains sixteen target elements. Those target
elements 301 located at the edges and corners of the tag (twelve in
total) are shared by adjacent tags and define the perimeter of the
tag. The high number of target elements 301 advantageously
facilitates accurate determination of a perspective distortion of
the tag 4 when it is imaged by the sensing device 400. This
improves the accuracy of tag sensing and, ultimately, position
determination.
[0207] The tag 4A consists of a square array of nine symbol groups
303. Symbol groups 303 are demarcated by the target elements 301 so
that each symbol group is contained within a square defined by four
target elements. Adjacent symbol groups 303 are contiguous and
share targets.
[0208] Since the target elements 301 are all identical, they do not
demarcate one tag from its adjacent tags. Viewed purely at the
level of target elements, only symbol groups 303, which define
cells of a target grid, can be distinguished--the tags 4A
themselves are indistinguishable by viewing only the target
elements. Hence, tags 4A must be aligned with the target grid as
part of tag decoding.
[0209] The tag 4A is designed to allow all tag data, with the
exception of an embedded data object (see Section 3.9.3), to be
recovered from an imaging field of view substantially the size of
the tag.
3.3 Symbol Groups
[0210] As shown in FIG. 4, each of the nine symbol groups 303
comprises twelve data symbols 304A, each data symbol being part of
a codeword. In addition, each symbol group 303 comprises a pair of
registration symbols--a vertical registration symbol (`VRS`) and a
horizontal registration symbol (`HRS`). These allow the orientation
and/or translation of the tag 4A in the field of view to be
determined. Translation refers to the translation of tag(s)
relative to the symbol groups 303 in the field of view. In other
words, the registration symbols enable alignment of the `invisible`
tags with the target grid.
[0211] Each data symbol 304A is a multi-pulse position modulated
(PPM) data symbol. Typically, each PPM data symbol 304A encodes a
single 4-bit Reed-Solomon symbol using 3 macrodots in any of 6
positions {p.sub.0, p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5},
i.e. using 3-6 pulse-position modulation (PPM). However, it will be
appreciated that other forms of multi-PPM encoding are equally
possible.
[0212] 3-6 PPM has a range of 20 codes, or 4.3 bits, and is used
for Reed-Solomon data symbols and Reed-Solomon redundancy
symbols.
[0213] Each symbol group also contains a 2-6 PPM vertical
registration symbol (VRS) and a 2-6 PPM horizontal registration
symbol (HRS). These allow the orientation and translation of the
tag in the field of view to be determined. This is described in
more detail in Section 3.6.1.
[0214] FIG. 5 shows the layout for a 2-6 PPM or 3-6 PPM data symbol
304.
[0215] Table 1 defines the mapping from 3-6 PPM symbol values to
Reed-Solomon symbol values. Unused symbol values can be treated as
erasures.
TABLE-US-00002 TABLE 1 3-6PPM to Reed-Solomon symbol mapping
Corresponding Reed-Solomon 3-6PPM symbol symbol value value
(p.sub.5-p.sub.0) (base 16) 000111 unused 001011 unused 001101 0
001110 1 010011 2 010101 3 010110 4 011001 5 011010 6 011100 7
100011 8 100101 9 100110 a 101001 b 101010 c 101100 d 110001 e
110010 f 110100 unused 111000 unused
3.4 Targets and Macrodots
[0216] The spacing of macrodots 302 in both dimensions, as shown in
FIG. 6, is specified by the parameter s. It has a nominal value of
127 .mu.m, based on 8 dots printed at a pitch of 1600 dots per
inch.
[0217] Only macrodots 302 are part of the representation of a
symbol 304A in the pattern. The outline of a symbol 304A is shown
in, for example, FIGS. 3 and 4 merely to elucidate more clearly the
structure of the tag 4A.
[0218] A macrodot 302 is nominally square with a nominal size of
(4/8)s. However, it is allowed to vary in size by .+-.10% according
to the capabilities of the device used to produce the pattern.
[0219] A target 301 is nominally circular with a nominal diameter
of (12/8)s. However, it is allowed to vary in size by 110%
according to the capabilities of the device used to produce the
pattern.
[0220] Each symbol group 303 has a width of 10s. Therefore, each
tag 4A has a width of 30s and a length of 30s. However, it should
be noted from FIG. 3 that the tag 4A is configured so that some
data symbols 304A extend beyond the perimeter edge of the tag 4A by
one macrodot unit (is), and interlock with complementary data
symbols from adjacent tags. This arrangement provides a tessellated
pattern of data symbols 304A within the target grid. From a data
acquisition standpoint, tessellation of data symbols in this way
increases the effective length of each tag 4A by one macrodot
unit.
[0221] The macrodot spacing, and therefore the overall scale of the
tag pattern, is allowed to vary between 127 .mu.m and 120 .mu.m
according to the capabilities of the device used to produce the
pattern. Any deviation from the nominal scale is recorded in each
tag (via a macrodot size ID field) to allow accurate generation of
position samples.
[0222] These tolerances are independent of one another. They may be
refined with reference to particular printer characteristics.
3.5 Field of View
[0223] As mentioned above, the tag 4A is designed to allow all tag
data to be recovered from an imaging field of view roughly the size
of the tag. Any data common to a set of contiguous tags only needs
to appear once within each tag, since fragments of the common data
can be recovered from adjacent tags. Any data common only to a
column or row of tags may appear twice within the tag--i.e. once in
each horizontal half or vertical half of the tag respectively.
However, special symbol arrangements may be used to ameliorate this
requirement, as described in more detail in Section 3.6.3. Finally,
any data unique to the tag must appear four times within the
tag--i.e. once in each quadrant.
[0224] Although data which is common to a set of tags, in one or
both spatial dimensions, may be decoded from fragments from
adjacent tags, pulse-position modulated values are best decoded
from spatially-coherent samples (i.e. from a whole symbol as
opposed to partial symbols at opposite sides of the field of view),
since this allows raw sample values to be compared without first
being normalised. This implies that the field of view must be large
enough to contain two complete copies of each such pulse-position
modulated value. The tag is designed so that the maximum extent of
a pulse-position modulated value is three macrodots (see FIG. 3).
Making the field of view at least as large as the tag plus three
macrodot units guarantees that pulse-position modulated values can
be coherently sampled.
[0225] The only exceptions are the translation codes described in
the next section, which are four macrodot units long. However,
these are highly redundant and the loss of up to four symbols at
the edge of the field of view is not a problem.
3.6 Encoded Codes and Codewords
[0226] In this section (Section 3.6), each symbol in FIGS. 8 to 12
is shown with a unique label. The label consists of an alphabetic
prefix which identifies which codeword the symbol is part of, and a
numeric suffix which indicates the index of the symbol within the
codeword. For simplicity only data symbols 304A are shown, not
registration symbols.
[0227] Although some symbol labels are shown rotated to indicate
the symmetry of the layout of certain codewords, the layout of each
symbol is determined by its position within a symbol group and not
by the rotation of the symbol label (as described in, for example,
the Applicant's US Publication No. 2006/146069).
3.6.1 Registration Symbols
[0228] Each registration symbol is encoded using 2-6 PPM. FIG. 7
shows the layout of the registration symbol.
[0229] As shown in FIG. 4, the horizontal and vertical registration
symbols each appear once within a symbol group 303. The
registration symbols of an entire tag typically indicate the
vertical and horizontal translation of the tag by coding two
orthogonal translation codes, and the orientation of the tag by
coding two orthogonal direction codes.
[0230] Each registration symbol may also encode a one-bit symbol of
a flag code (see Section 3.6.2).
[0231] Table 2 defines the mapping from 2-6 PPM registration symbol
values to flag code, direction code and translation code symbol
values.
TABLE-US-00003 TABLE 2 2-6PPM registration symbol values to flag
code, direction code and translation code symbol mapping 2-6PPM
translation direction flag code symbol value code symbol code
symbol symbol {p.sub.5-p.sub.0} value value value 001, 001 0 0
unspecified 100, 010 1 001, 010 1 0 0 000, 101 1 010, 100 1 0 101,
000 1 010, 001 2 0 unspecified 100, 100 1 000, 011 3 0 000, 110 1
011, 000 4 0 110, 000 1 001, 100 unused 010, 010 100, 001
[0232] The first position-coding pattern ("Yarrow") uses the first
eight registration symbol values in Table 2 i.e. those registration
symbol values mapping to a translation code symbol value of 0, 1 or
2. In other words, if the registration symbol value maps to a
translation code symbol value of 0, 1 or 2, then the
position-coding pattern is identified as the first position-coding
pattern having 9 symbol groups 303 contained in one tag 4A.
[0233] The additional translation code symbol values (i.e. 3 and 4)
shown in Table 2 are reserved for the second position-coding
pattern ("Saffron") described in Section 4.6.1. Thus, if the
registration symbol value maps to a translation code symbol value
of 3 or 4, then the position-coding pattern is identified as the
second position-coding pattern having 4 symbol groups 303 contained
in one tag 4B. In this way, the registration symbol provides a
means of distinguishing the first position-coding pattern from the
second position-coding pattern. Subsequent decoding of PPM data
symbols proceeds in accordance with the position-coding pattern
identified from decoding the registration symbol(s).
[0234] In the first position-coding pattern, each row of symbol
groups and each column of symbol groups encodes a three-symbol
3-ary cyclic position code. (The Applicant's cyclic position codes
are described in U.S. Pat. No. 7,082,562, the contents of which is
herein incorporated by reference). The code consists of the
codeword (0, 1, 2) and its cyclic shifts. The code has a minimum
distance of 3, allowing a single symbol error to be corrected. For
each of the two orthogonal translations, the three translation
codes of an entire tag form a code with a minimum distance of 9,
allowing 4 symbol errors to be corrected. If additional symbols are
visible within the field of view then they can be used for
additional redundancy.
[0235] The translation code symbol in the middle of the codeword
(i.e. 1) is mapped to a set of 2-6 PPM symbol values that are each
other's reverse, while the two translation code symbols at the ends
of the codeword (i.e. 0 and 2) are each mapped to a set of 2-6 PPM
symbol values that are the reverses of the 2-6 PPM symbol values in
the other set. Thus a 0 read upside-down (i.e. rotated 180 degrees)
becomes a 2, and vice versa, while a 1 read upside-down remains a
1. This allows translation to be determined independently of
rotation.
[0236] Furthermore, in the first position-coding pattern, each 2-6
PPM symbol value and its reverse map to opposite direction code
symbol values (Table 2). The vertical registration symbols of an
entire tag encode 9 symbols of a vertical direction code. This has
a minimum distance of 9, allowing 4 symbol errors to be corrected.
The horizontal registration symbols of an entire tag encode 9
symbols of a horizontal direction code. This has a minimum distance
of 9, allowing 4 symbol errors to be corrected. If additional
symbols are visible within the field of view then they can be used
for additional redundancy. Any erasures detected during decoding of
a translation code can also be used during decoding of a direction
code, and vice versa. Together the orthogonal direction codes allow
the orientation of the tag to be determined.
[0237] The top left corner of an un-rotated tag is identified by a
symbol group whose translation symbols are both zero and whose
direction symbols are both zero.
3.6.2 Active Area Flag Code
[0238] The flag symbol consists of one bit of data, and is encoded
in some of the vertical and horizontal registration symbols, as
shown in Table 2.
[0239] The flag symbol is unique to a tag and is therefore coded
redundantly in each quadrant of the tag. Since the flag symbol is
encoded in each registration code symbol, it appears four times
within each quadrant (assuming the central registration code
symbols participate in each quadrant, as usually supported by the
minimum field of view). Four symbols form a code with a minimum
distance of 4, allowing 1 error to be corrected. If additional
symbols are visible within the field of view then they can be used
for additional redundancy. Any errors detected during decoding of
translation and/or direction codes can also be used to flag
erasures during decoding of the flag code. Since the flag code
encodes the active area flag, it can meaningfully be interpreted as
set even if ambiguous.
3.6.3 Coordinate Data
[0240] The tag 4A contains an x-coordinate codeword and a
y-coordinate codeword used to encode the x and y coordinates of the
tag respectively. The codewords are of a shortened 2.sup.4-ary (11,
3) or (11, 5) Reed-Solomon code. The tag therefore encodes either
12-bit or 20-bit coordinates. An (11, 5) code is used if the
<region has long coordinates> flag in the region flags is set
(see Table 5). An (11, 3) code is used otherwise.
[0241] Each x coordinate codeword is replicated twice within the
tag--in each horizontal half ("north" and "south"), and is constant
within the column of tags containing the tag. Likewise, each y
coordinate codeword is replicated twice within the tag--in each
vertical half ("east" and "west"), and is constant within the row
of tags containing the tag. This guarantees that an image of the
tag pattern large enough to contain a complete tag is guaranteed to
contain a complete instance of each coordinate codeword,
irrespective of the alignment of the image with the tag pattern.
The instance of either coordinate codeword may consist of fragments
from different tags.
[0242] It should be noted that, in the first position-coding
pattern, some coordinate symbols are not replicated and are placed
on the dividing line between the two halves of the tag. This
arrangement saves tag space since there are not two complete
replications of each x-coordinate codeword and each y-coordinate
codeword contained in a tag. Since the field of view is at least
three macrodot units larger than the tag (as discussed in Section
3.10), the coordinate symbols placed on the dividing line (having a
width 2 macrodot units) are still captured when the surface is
imaged. Hence, each interaction with the coded surface still
provides the tag location.
[0243] The layout of the x-coordinate codeword is shown in FIG. 8.
The layout of the y-coordinate codeword is shown in FIG. 9. It can
be seen that x-coordinate symbols X4, X5, X6, X7, X8 and X9 are
placed in a central column 310 of the tag 4A, which divides the
eastern half of the tag from the western half. Likewise, the
y-coordinate symbols Y4, Y5, Y6, Y7, Y8 and Y9 are placed in a
central row 312 of the tag 4A, which divides the northern half of
the tag from the southern half.
[0244] The central column 310 and central row 312 each have a width
q, which corresponds to a width of 2s, where s is the macrodot
spacing.
3.6.4 Common Data
[0245] The tag 4A contains four codewords A, B, C and D which
encode information common to a set of contiguous tags in a surface
region. The A codeword is of a 2.sup.4-ary (15, 5) Reed-Solomon
code. The B, C and D codewords are of a 2.sup.4-ary (15, 7) or (15,
9) Reed-Solomon code. The tag therefore encodes either 112 or 136
bits of information common to a set of contiguous tags. A (15, 9)
code is used for the B, C and D codewords if the <region has a
long region ID> flag in the region flags is set (see Table 6). A
(15, 7) code is used otherwise.
[0246] The common codewords are replicated throughout a tagged
region. This guarantees that an image of the tag pattern large
enough to contain a complete tag is guaranteed to contain a
complete instance of each common codeword, irrespective of the
alignment of the image with the tag pattern. The instance of each
common codeword may consist of fragments from different tags.
[0247] The layout of the common codewords is shown in FIG. 10. The
codewords have the same layout, rotated 90 degree relative to each
other.
3.6.5 Optional Data
[0248] The tag optionally contains a codeword E. This codeword may
be used to encode a secret-key signature or a fragment of an
embedded data object. These are discussed further in Sections 3.6.6
and Section 3.9.3 respectively. The codeword is of a 2.sup.4-ary
(15, 9) Reed-Solomon code.
[0249] The layout of the optional codeword is shown in FIG. 11.
3.6.6 Secret-Key Signature
[0250] The tag optionally contains an entire secret-key digital
signature common to a set of contiguous tags in a surface region.
The signature consists of sixteen 2.sup.4-ary symbols (i.e. symbol
E15 is also used). The tag therefore optionally encodes up to 64
bits of secret-key signature data.
[0251] The signature is replicated throughout a tagged region. This
guarantees that an image of the tag pattern large enough to contain
a complete tag is guaranteed to contain a complete instance of the
signature, irrespective of the alignment of the image with the tag
pattern. The instance of the signature may consist of fragments
from different tags.
[0252] The signature, if present, is encoded in the E codeword
described in Section 3.6.5.
[0253] Digital signatures are discussed further in Section
3.9.4.
3.6.7 Complete Tag
[0254] FIG. 12 shows the layout of the data of a complete tag, with
each symbol group comprising ten data symbols. The vertical and
horizontal registration symbols are not shown in FIG. 12.
3.7 Reed-Solomon Encoding
3.7.1 Reed-Solomon Codes
[0255] All data is encoded using a Reed-Solomon code defined over
GF(2.sup.4). The code has a natural length n of 15. The dimension k
of the code is chosen to balance the error correcting capacity and
data capacity of the code, which are (n-k)/2 and k symbols
respectively.
[0256] The code may be punctured, by removing high-order redundancy
symbols, to obtain a code with reduced length and reduced error
correcting capacity. The code may also be shortened, by replacing
high-order data symbols with zeros, to obtain a code with reduced
length and reduced data capacity. Both puncturing and shortening
can be used to obtain a code with particular parameters. Shortening
is preferred, where possible, since this avoids the need for
erasure decoding.
[0257] The code has the following primitive polynomial:
p(x)=x.sup.4+x+1
[0258] The code has the following generator polynomial:
g ( x ) = i = 1 n - k ( x + .alpha. i ) ##EQU00001##
[0259] For a detailed description of Reed-Solomon codes, refer to
Wicker, S. B. and V. K. Bhargava, eds., Reed-Solomon Codes and
Their Applications, IEEE Press, 1994.
3.7.2 Codeword Organization
[0260] As shown in FIG. 13, redundancy coordinates r.sub.i and data
coordinates di of the code are indexed from left to right according
to the power of their corresponding polynomial terms. The symbols
X.sub.i of a complete codeword are indexed from right to left to
match the bit order of the data. The bit order within each symbol
is the same as the overall bit order.
3.7.3 Code Instances
[0261] Table 3 defines the parameters of the different codes used
in the tag.
TABLE-US-00004 TABLE 3 Codeword instances error- correcting data
length dimension capacity capacity.sup.a name description (n) (k)
(symbols) (bits) X, Y coordinate .sup. 11.sup.a 3 4 12 codewords
(see 5 3 20 Section 3.6.3) A first common 15 5 5 20 codeword B, C,
D other common 15 7 3 28 codewords (see 9 3 36 Section 3.6.4) E
optional 15 9 3 36 codeword (see Section 3.6.5) .sup.ashortened
3.7.4 Cyclic Redundancy Check
[0262] The region ID is protected by a 16-bit cyclic redundancy
check (CRC). This provides an added layer of error detection after
Reed-Solomon error correction, in case a codeword containing a part
of the region ID is mis-corrected.
[0263] The CRC has the following generator polynomial:
g(x)=x.sup.16+x.sup.12+x.sup.5+1
[0264] The CRC is initialised to 0xFFFF. The most significant bit
of the region ID is treated as the most significant coefficient of
the data polynomial.
3.8 Tag Coordinate Space
[0265] The tag coordinate space has two orthogonal axes labelled x
and y respectively. When the positive x axis points to the right
then the positive y axis points down.
[0266] The surface coding does not specify the location of the tag
coordinate space origin on a particular tagged surface, nor the
orientation of the tag coordinate space with respect to the
surface. This information is application-specific. For example, if
the tagged surface is a sheet of paper, then the application which
prints the tags onto the paper may record the actual offset and
orientation, and these can be used to normalise any digital ink
subsequently captured in conjunction with the surface.
[0267] The position encoded in a tag is defined in units of tags
and is defined to be the centre of the top left target. The origin
of a particular tag pattern is therefore the centre of the top left
target of the tag that encodes coordinate pair (0, 0).
[0268] The surface coding is optionally displaced from its nominal
position relative to the surface by an amount derived from the
region ID. This ensures that the utilisation of a pagewidth digital
printhead used to print the surface coding is uniform. The
displacement of the surface coding is negative, hence the
displacement of the region described by the surface coding is
positive relative to the surface coding. The magnitude of the
displacement is the region ID modulo the width of the tag in 1600
dpi dots (i.e. 240). To accommodate non-1600 dpi printers the
actual magnitude of the displacement may vary from its nominal
value by up to half the dot pitch of the printer.
3.9 Tag Information Content
3.9.1 Field Definitions
[0269] Table 4 defines the information fields embedded in the first
position-coding pattern.
TABLE-US-00005 TABLE 4 Field Definitions width field (bits)
description unique to tag active area flag 1 A flag indicating
whether the area.sup.a immediately surrounding a tag intersects an
active area. x coordinate 12 or The unsigned x coordinate of the
tag.sup.b. 20 y coordinate 12 or The unsigned y coordinate of the
tag.sup.b. 20 common to tagged region encoding 2 The format of the
encoding. format 0: the present encoding. Other values are reserved
region flags 10 Flags controlling the interpretation of region data
(see Table 5). coordinate 2 A value (p) indicating the precision of
x and y precision coordinates according to the formula 8 + 4p.
macrodot size 4 The ID of the macrodot size. ID region ID 72 or The
ID of the region containing the tags. 96 CRC 16 A CRC of the region
ID (see Section 3.7.4) secret-key 64 An optional secret-key
signature of the region. signature .sup.athe diameter of the area,
centered on the tag, is nominally 2.5 times the diagonal size of
the tag; this is to accommodate the worst-case distance between the
nib position and the imaged tag .sup.ballows a coordinate value
ranges of 14.8 m and 3.8 km for the minimum tag size of 3.6 mm
(based on the minimum macrodot size of 120 microns and 30 macrodots
per tag)
[0270] An active area is an area within which any captured input
should be immediately forwarded to the corresponding Netpage server
10 for interpretation. This also allows the Netpage server 10 to
signal to the user that the input has had an immediate effect.
Since the server has access to precise region definitions, any
active area indication in the surface coding can be imprecise so
long as it is inclusive.
TABLE-US-00006 TABLE 5 Region flags bit meaning 0 Region is
interactive, i.e. x and y-coordinates are present. 1 Region is
active, i.e. the entire region is an active area. Otherwise active
areas are identified by individual tags' active area flags. 2
Region ID is not serialized.sup.a. 3 Region has secret-key
signature (see Section 3.9.4) 4 Region has embedded data. 5
Embedded data is a public-key signature (see Sections 3.9.3 and
3.9.4). 6 Region has long coordinates.sup.b. 7 Region has a long
region ID.sup.c. 8 Region ID is an EPC. 9 Region is displaced
according to region ID .sup.aFor an EPC this means that the serial
number is replaced by a layout number, to allow the package design
associated with a product to vary over time (see US 2007/0108285,
the contents of which is herein incorporated by reference).
.sup.bHence the X and Y Reed-Solomon codewords have less
redundancy. .sup.cHence, the B, C and D Reed-Solomon codewords have
less redundancy.
3.9.2 Mapping of Fields to Codewords
[0271] Table 6, Table 7 and Table 8 define how the information
fields map to codewords in the first position-coding pattern.
TABLE-US-00007 TABLE 6 Mapping of fields to coordinate codewords X
and Y X and Y codeword data codeword codeword field capacity field
width field bits bits X x coordinate 12 all all 20 Y y coordinate
12 all all 20
TABLE-US-00008 TABLE 7 Mapping of fields to common codewords A, B,
C and D A, B, C and D codeword data field field codeword codeword
field capacity width bits bits A encoding format any 2 all 1:0
region flags 10 all 11:2 macrodot size ID 4 all 15:12 region ID 28
4 71:68 19:16 36 95:92 B CRC any 16 all 15:0 region ID 28 12 11:0
27:16 36 20 19:0 35:16 C region ID 28 39:12 all 36 55:20 D region
ID 28 67:40 all 36 91:56
TABLE-US-00009 TABLE 8 Mapping of fields to optional codeword E E
codeword data field codeword codeword field capacity width field
bits bits E data fragment 36.sup. all all secret-key digital
64.sup.a all all signature .sup.aEntire codeword (including
16.sup.th symbol) is used for data i.e. there is no redundancy
[0272] As shown in Table 8, codeword E either contains a data
fragment or a secret-key signature. These are described in Section
3.9.3 and Section 3.9.4 respectively. The secret-key signature is
present in a particular tag if the <region has secret-key
signature> flag in the region flags is set, and the tag's active
area flag is set. The data fragment is present in a particular tag
if the <region contains embedded data> flag in the region
flags is set and the tag does not already contain a secret-key
signature.
[0273] When the region flags indicate that a particular codeword is
absent then the codeword is not coded in the tag pattern, i.e.
there are no macrodots representing the codeword. This applies to
the X, Y and E codewords i.e. the X and Y codewords are present if
the <region is interactive> flag in the region flags is set.
The E codeword is present if a secret-key signature or data
fragment is present.
3.9.3 Embedded Data Object
[0274] If the <region has embedded data> flag in the region
flags is set then the surface coding contains embedded data. The
embedded data is encoded in multiple contiguous tags' data
fragments, and is replicated in the surface coding as many times as
it will fit.
[0275] The embedded data is encoded in such a way that a random and
partial scan of the surface coding containing the embedded data can
be sufficient to retrieve the entire data. The scanning system
reassembles the data from retrieved fragments, and reports to the
user when sufficient fragments have been retrieved without
error.
[0276] As shown in Table 9, each block has a data capacity of
176-bits. The block data is encoded in the data fragments of a
contiguous group of six tags arranged in a 3.times.2 rectangle.
[0277] The block parameters are as defined in Table 9. The E
codeword of each tag may encode a fragment of the embedded
data.
TABLE-US-00010 TABLE 9 Block parameters parameter value description
w 3 The width of the block, in tags h 2 The height of the block, in
tags. b 176 The data capacity of the block, in bits
[0278] If the E codeword of a particular tag does not contain a
fragment of the embedded data, then the pen 400 can discover this
implicitly by the failure of the codeword to decode, or explicitly
from the tag's active area flag.
[0279] Data of arbitrary size may be encoded into a superblock
consisting of a contiguous set of blocks, typically arranged in a
rectangle. The size of the superblock may be encoded in each
block.
[0280] The superblock is replicated in the surface coding as many
times as it will fit, including partially along the edges of the
surface coding.
[0281] The data encoded in the superblock may include, for example,
more precise type information, more precise size information, and
more extensive error detection and/or correction data.
3.9.4 Digital Signatures
[0282] As described in Section 3.6.6, a region may contain a
digital signature.
[0283] If the <region has a secret-key signature> flag in the
region flags is set, then the region has a secret-key digital
signature. In an online environment the secret-key signature can be
verified, in conjunction with the region ID, by querying a server
with knowledge of the secret-key signature or the corresponding
secret key.
[0284] If the region contains embedded data and the <embedded
data is a public-key signature> flag in the region flag is set,
then the surface coding contains an embedded public-key digital
signature of the region ID.
[0285] In an online environment any number of signature fragments
can be used, in conjunction with the region ID and optionally the
secret-key signature, to validate the public-key signature by
querying a server with knowledge of the full public-key signature
or the corresponding private key.
[0286] In an offline (or online) environment the entire public-key
signature can be recovered by reading multiple tags, and can then
be verified using the corresponding public signature key. The
actual length and type of the signature are determined from the
region ID during signature validation i.e. typically from a
previously-retrieved digital signature associated with a sequence
of region IDs.
[0287] Digital signature verification is discussed in the
Applicant's US Publication No. 2007/0108285, the contents of which
are herein incorporated by reference.
3.10 Tag Imaging
[0288] The minimum imaging field of view required to guarantee
acquisition of data from an entire tag 4A has a diameter of 46.7s
(i.e. ((3.times.10)+3) 2s), allowing for arbitrary rotation and
translation of the surface coding in the field of view. Notably,
the imaging field of view does not have to be large enough to
guarantee capture of an entire tag--the arrangement of the data
symbols within each tag ensures that a any square portion of length
(l+3s) captures the requisite information in full, irrespective of
whether a whole tag is actually visible in the field-of-view. As
used herein, l is defined as the length of a tag.
[0289] In terms of imaging the coding pattern, the imaging
field-of-view is typically a circle. Accordingly, the imaging
field-of-view should preferably have diameter of at least (l+3s) 2
and less than two tag diameters. Importantly, the field-of-view is
not required to be at least two tag diameters, in contrast with
prior art tag designs, because it is not essential to capture an
entire tag 4A in the field of view.
[0290] The extra three macrodot units ensure that pulse-position
modulated values can be decoded from spatially coherent samples.
Furthermore, the extra three macrodot units ensure that all
requisite data symbols 304A can be read with each interaction.
These include the coordinate symbols from a central column or row
of a tag (see Section 3.6.3) having a width of 2s.
[0291] In the present context, a "tag diameter" is given to mean
the length of a tag diagonal.
[0292] Given a maximum macrodot spacing of 127 microns, this gives
a required field of view of 5.93 mm.
4 Second Position--Coding Pattern ("Saffron")
4.1 Background
[0293] As will be appreciated from the following description, the
second position-coding pattern bears many similarities with the
first position coding pattern. The most notable difference is that
each tag comprises 4 rather than 9 symbol groups 303. Furthermore,
the registration symbols in the second position-coding pattern map
to translation code symbol values (3, 4) specifically identifying
the second position-coding pattern, as described earlier in Section
3.6.1.
[0294] The complete second position-coding pattern will now be
described in detail below.
4.2 General Tag Structure
[0295] In common with the first position-coding pattern, each tag
4B of the second position-coding pattern is represented by two
kinds of elements. Referring to FIGS. 14 and 15, the first kind of
element is a target element. Target elements in the form of target
dots 301 allow the tag 4B to be located in an image of a coded
surface, and allow the perspective distortion of the tag to be
inferred. The second kind of element is a data element in the form
of a macrodot 302 (see FIG. 6). The macrodots 302 encode data
values.
[0296] FIG. 14 shows the structure of a complete tag 4B from the
second position-coding pattern, with target elements 301 shown. The
tag 4B is square and contains nine target elements. Those target
elements 301 located at the edges and corners of the tag (eight in
total) are shared by adjacent tags and define the perimeter of the
tag 4B.
[0297] The tag 4B consists of a square array of four symbol groups
303. Symbol groups 303 are demarcated by the target elements 301 so
that each symbol group is contained within a square defined by four
target elements. Adjacent symbol groups 303 are contiguous and
share targets.
[0298] Since the target elements 301 are all identical, they do not
demarcate one tag from its adjacent tags. Viewed purely at the
level of target elements, only symbol groups 303, which define
cells of a target grid, can be distinguished--the tags 4B
themselves are indistinguishable by viewing only the target
elements. Hence, tags 4B must be aligned with the target grid as
part of tag decoding.
[0299] The tag 4B is designed to allow all tag data to be recovered
from an imaging field of view substantially the size of the
tag.
4.3 Symbol Groups
[0300] As shown in FIG. 15, each of the nine symbol groups 303
comprises eight data symbols 304B, each data symbol being part of a
codeword. In addition, each symbol group 303 comprises a pair of
registration symbols--a vertical registration symbol (`VRS`) and a
horizontal registration symbol (`HRS`). These allow the orientation
and/or translation of the tag 4B in the field of view to be
determined.
[0301] Each data symbol 304B is a multi-pulse position modulated
(PPM) data symbol. Typically, each PPM data symbol 304B encodes
5-bits using 2-9 PPM encoding. i.e. 2 macrodots in any of 9
positions {p.sub.0, p.sub.2, p.sub.3, p.sub.4, p.sub.5, p.sub.6,
p.sub.7, p.sub.8}
[0302] FIG. 16 shows the layout for a 2-9 PPM data symbol 304B.
[0303] Each symbol group also contains a 2-6 PPM vertical
registration symbol (VRS) and a 2-6 PPM horizontal registration
symbol (HRS), as described in Sections 3.3 and 3.6.1 above.
[0304] Table 10 defines the mapping from 2-6 PPM symbol values to
data symbol values. Unused symbol values can be treated as
erasures.
TABLE-US-00011 TABLE 10 2-9PPM symbol to data symbol value mapping
2-9PPM symbol value data symbol value (p.sub.8-p.sub.0) (base 16)
000, 000, 011 0 000, 000, 101 1 000, 000, 110 2 000, 001, 001 3
000, 001, 010 4 000, 001, 100 5 000, 010, 001 6 000, 010, 010 7
000, 010, 100 8 000, 011, 000 9 000, 100, 001 a 000, 100, 010 b
000, 100, 100 c 000, 101, 000 d 000, 110, 000 e 001, 000, 001 f
001, 000, 010 10 001, 000, 100 11 001, 001, 000 12 001, 010, 000 13
001, 100, 000 14 010, 000, 001 15 010, 000, 010 16 010, 000, 100 17
010, 001, 000 18 010, 010, 000 19 010, 100, 000 1a 011, 000, 000 1b
100, 000, 001 1c 100, 000, 010 1d 100, 000, 100 1e 100, 001, 000 1f
100, 010, 000 unused 100, 100, 000 unused 101, 000, 000 unused 110,
000, 000 unused
4.4 Targets and Macrodots
[0305] The spacing of macrodots 302 in both dimensions, as shown in
FIG. 6, is specified by the parameter s. In the second
position-coding pattern, it has a nominal value of 159 .mu.m, based
on 10 dots printed at a pitch of 1600 dots per inch.
[0306] A macrodot 302 is nominally square with a nominal size of
(5/10)s. However, it is allowed to vary in size by 110% according
to the capabilities of the device used to produce the pattern.
[0307] A target 301 is nominally circular with a nominal diameter
of (15/10)s. However, it is allowed to vary in size by 110%
according to the capabilities of the device used to produce the
pattern.
[0308] Each symbol group 303 has a width of 10s. Therefore, each
tag 4B has a width of 20s and a length of 20s. However, it should
be noted from FIG. 15 that the tag 4B is configured so that some
data symbols 304 extend beyond the perimeter edge of the tag 4B by
one macrodot unit (1s), and interlock with complementary data
symbols from adjacent tags. This arrangement provides a tessellated
pattern of data symbols 304A within the target grid. From a data
acquisition standpoint, tessellation of data symbols in this way
increases the effective length of each tag 4B by one macrodot
unit.
[0309] The macrodot spacing, and therefore the overall scale of the
tag pattern, is allowed to vary between 152 .mu.m and 169 .mu.m
according to the capabilities of the device used to produce the
pattern. Any deviation from the nominal scale is recorded in each
tag (via a macrodot size ID field) to allow accurate generation of
position samples.
[0310] These tolerances are independent of one another. They may be
refined with reference to particular printer characteristics.
4.5 Field of View
[0311] As mentioned above, the tag 4B is designed to allow all tag
data to be recovered from an imaging field of view roughly the size
of the tag.
[0312] Although data which is common to a set of tags, in one or
both spatial dimensions, may be decoded from fragments from
adjacent tags, pulse-position modulated values are best decoded
from spatially-coherent samples (i.e. from a whole symbol as
opposed to partial symbols at opposite sides of the field of view),
since this allows raw sample values to be compared without first
being normalised. This implies that the field of view must be large
enough to contain two complete copies of each such pulse-position
modulated value. The tag is designed so that the maximum extent of
a pulse-position modulated value is four macrodots. Making the
field of view at least as large as the tag plus four macrodot units
guarantees that pulse-position modulated values can be coherently
sampled.
4.6 Encoded Codes and Codewords
[0313] In this section (Section 4.6), each symbol in FIGS. 17 to 20
is shown with a unique label. The label consists of an alphabetic
prefix which identifies which codeword the symbol is part of, and a
numeric suffix which indicates the index of the symbol within the
codeword. For simplicity only data symbols 304B are shown in FIGS.
17 to 20, not registration symbols.
[0314] Although some symbol labels are shown rotated to indicate
the symmetry of the layout of certain codewords, the layout of each
symbol is determined by its position within a symbol group and not
by the rotation of the symbol label (as described in, for example,
the Applicant's US Publication No. 2006/146069).
4.6.1 Registration Symbols
[0315] Each registration symbol of the second position-coding
pattern is encoded using 2-6 PPM, as described above in Section
3.6.1 and FIG. 7. Furthermore, each registration symbol of the
second position-coding pattern is positioned and configured in the
same way as each registration symbol of the first position-coding
pattern. However, the second position-coding pattern utilizes only
those registration symbol values mapping to the translation code
symbol values (3, 4). This enables the registration symbol to
identify the second position-coding pattern, and distinguish it
from the first position-coding pattern.
[0316] In other words, if the registration symbol value maps to a
translation code symbol value of 3 or 4, then the position-coding
pattern is identified as the second position-coding pattern having
4 symbol groups 304B contained in one tag 4B.
[0317] In the first position-coding pattern, each row of symbol
groups and each column of symbol groups encodes a two-symbol 2-ary
cyclic position code. (The Applicant's cyclic position codes are
described in U.S. Pat. No. 7,082,562, the contents of which is
herein incorporated by reference). The code consists of the
codeword (3, 4) and its cyclic shifts. For each of the two
orthogonal translations, the two translation codes of an entire tag
form a code with a minimum distance of 4, allowing 1 symbol error
to be corrected. If additional symbols are visible within the field
of view then they can be used for additional redundancy.
[0318] The two translation code symbols (3 and 4) are each mapped
to a set of 2-6 PPM symbol values that are the reverses of the 2-6
PPM symbol values in the other set. Thus a 3 read upside-down (i.e.
rotated 180 degrees) becomes a 4, and vice versa. This allows
translation to be determined independently of rotation.
[0319] Furthermore, in the first position-coding pattern, each 2-6
PPM symbol value and its reverse map to opposite direction code
symbol values (Table 2). The vertical registration symbols of an
entire tag encode 4 symbols of a vertical direction code. This has
a minimum distance of 4, allowing 1 symbol error to be corrected.
The horizontal registration symbols of an entire tag encode 4
symbols of a horizontal direction code. This has a minimum distance
of 4, allowing 1 symbol error to be corrected. If additional
symbols are visible within the field of view then they can be used
for additional redundancy. Any erasures detected during decoding of
a translation code can also be used during decoding of a direction
code, and vice versa. Together the orthogonal direction codes allow
the orientation of the tag to be determined.
[0320] The top left corner of an un-rotated tag is identified by a
symbol group whose translation symbols are both zero and whose
direction symbols are both zero.
[0321] Although as shown in Table 2, the 2-6 PPM registration
symbol does not allow flag codes for the second position-coding
pattern, it will be appreciated that a 3-6 PPM registration symbol
mapping to 20 available symbol values would allow the second
position-coding pattern to contain flag codes, if desired. In this
case, 12 registration symbol values (3.times.2.times.2) would be
used for the first position-coding pattern and 8 registration
symbols value (2.times.2.times.2) would be used for the second
position-coding pattern.
4.6.2 Coordinate Data
[0322] The tag 4B contains an x-coordinate codeword and a
y-coordinate codeword used to encode the x and y coordinates of the
tag respectively. The codewords are of a shortened 2.sup.5-ary (4,
2) Reed-Solomon code. The tag therefore encodes 10-bit
coordinates.
[0323] Each x coordinate codeword is constant within the column of
tags containing the tag. Likewise, each y coordinate codeword is
constant within the row of tags containing the tag.
[0324] It should be noted that, in the second position-coding
pattern, none of the coordinate symbols are replicated. Instead,
all coordinate symbols are placed in either one column or one row
of the tag. This arrangement saves tag space since it obviates the
requirement for each tag to contain two complete replications of
each x-coordinate codeword and each y-coordinate codeword. Since
the field of view is at least four macrodot units larger than the
length of the tag, the coordinate symbols placed in a column or row
line having a width of three macrodot units are still captured when
the surface is imaged. Hence, each interaction with the coded
surface still provides the tag location. The instance of either
coordinate codeword may consist of fragments from different
tags.
[0325] FIG. 17 shows the layout of an x-coordinate codeword X. The
outline of the codeword X is shown in bold. It should be noted that
the entire x-coordinate codeword is encoded by data symbols X0, X1,
X2 and X3 contained in a single column 313 of width v. Likewise, as
shown in FIG. 18, the entire y-coordinate codeword is encoded by
data symbols Y0, Y1, Y2 and Y3 contained in a single row 315 of
width v.
[0326] The column of x-coordinate symbols and the row of
y-coordinate symbols each have a width v, which corresponds to a
width of 3s, where s is the macrodot spacing. Provided that an
imaged portion of the second position-coding pattern contains a
square of length (l+v), where l is the length of the tag, then the
imaged portion is guaranteed to contain the x-coordinate codeword
and the y-coordinate codeword.
4.6.3 Common Data
[0327] The tag 4B contains one codeword A which encodes information
common to a set of contiguous tags in a surface region. The A
codeword is of a shortened 2.sup.5-ary (24, 16) Reed-Solomon code.
The tag 4B therefore encodes 80 bits of information common to a set
of contiguous tags.
[0328] The common codeword is replicated throughout a tagged
region. This guarantees that an image of the tag pattern large
enough to contain a complete tag is guaranteed to contain a
complete instance of the common codeword, irrespective of the
alignment of the image with the tag pattern. The instance of the
common codeword may consist of fragments from different tags.
[0329] The layout of the common codeword is shown in FIG. 19.
4.6.3 Complete Tag
[0330] FIG. 20 shows the layout of the data of a complete tag 4B,
with each symbol group comprising eight data symbols. The vertical
and horizontal registration symbols are not shown in FIG. 20.
4.7 Reed-Solomon Encoding
4.7.1 Reed-Solomon Codes
[0331] All data of the second position-coding pattern is encoded
using a Reed-Solomon code defined over GF(2.sup.5). The code has a
natural length n of 31. The dimension k of the code is chosen to
balance the error correcting capacity and data capacity of the
code, which are (n-k)/2 and k symbols respectively.
[0332] The code may be punctured, by removing high-order redundancy
symbols, to obtain a code with reduced length and reduced error
correcting capacity. The code may also be shortened, by replacing
high-order data symbols with zeros, to obtain a code with reduced
length and reduced data capacity. Both puncturing and shortening
can be used to obtain a code with particular parameters. Shortening
is preferred, where possible, since this avoids the need for
erasure decoding.
[0333] The code has the following primitive polynomial:
p(x)=x.sup.5+x.sup.2+1
[0334] The code has the following generator polynomial:
g ( x ) = i = 1 n - k ( x + .alpha. i ) ##EQU00002##
[0335] For a detailed description of Reed-Solomon codes, refer to
Wicker, S. B. and V. K. Bhargava, eds., Reed-Solomon Codes and
Their Applications, IEEE Press, 1994.
4.7.2 Codeword Organization
[0336] As shown in FIG. 21, redundancy coordinates r.sub.i and data
coordinates di of the code are indexed from left to right according
to the power of their corresponding polynomial terms.
[0337] The symbols X.sub.i of a complete codeword are indexed from
right to left to match the bit order of the data. The bit order
within each symbol is the same as the overall bit order.
4.7.3 Code Instances
[0338] Table 11 defines the parameters of the different codes used
in the tag 4B.
TABLE-US-00012 TABLE 11 Codeword instances error- correcting data
length dimension capacity capacity.sup.a name description (n) (k)
(symbols) (bits) X, Y coordinate 4.sup.a 2 1 10 codewords (see
Section 4.6.3) A first common 24.sup.a 16 8 80 codeword
.sup.ashortened
4.7.4 Cyclic Redundancy Check
[0339] The region ID is protected by a 16-bit cyclic redundancy
check (CRC). This provides an added layer of error detection after
Reed-Solomon error correction, in case a codeword containing a part
of the region ID is mis-corrected.
[0340] The CRC has the following generator polynomial:
g(x)=x.sup.16+x.sup.12+x.sup.5+1
[0341] The CRC is initialised to 0xFFFF. The most significant bit
of the region ID is treated as the most significant coefficient of
the data polynomial.
4.8 Tag Coordinate Space
[0342] The tags 4B of the second position-coding pattern use a
coordinate space corresponding to the first position-coding pattern
having two orthogonal axes labelled x and y respectively. For a
further discussion, see Section 3.8 above.
4.9 Tag Information Content
4.9.1 Field Definitions
[0343] Table 12 defines the information fields embedded in the
second position-coding pattern.
TABLE-US-00013 TABLE 12 Field Definitions width field (bits)
description unique to tag x coordinate 10 The unsigned x coordinate
of the tag.sup.a. y coordinate 10 The unsigned y coordinate of the
tag.sup.a. common to tagged region encoding format 2 The format of
the encoding. 0: the present encoding. Other values are reserved
region flags 6 Flags controlling the interpretation of region data
(see Table 13). macrodot size ID 4 The ID of the macrodot size.
region ID 52 The ID of the region containing the tags. CRC 16 A CRC
of the region ID (see Section 4.7.4) .sup.aallows a coordinate
value ranges of 3.1 m for the minimum tag size of 3.04 mm (based on
the minimum macrodot size of 152 microns and 20 macrodots per
tag)
TABLE-US-00014 TABLE 13 Region flags bit meaning 0 Region is
interactive, i.e. x and y-coordinates are present. 1 Region is
active, i.e. the entire region is an active area. 2 Region ID is
serialized 3 Region is displaced according to region ID other
Reserved for future use.
4.9.2 Mapping of Fields to Codewords
[0344] Tables 14 and 15 define how the information fields map to
codewords in the second position-coding pattern.
TABLE-US-00015 TABLE 14 Mapping of fields to coordinate codewords X
and Y X and Y codeword data codeword codeword field capacity field
width field bits bits X x coordinate 10 all all Y y coordinate 10
all all
TABLE-US-00016 TABLE 15 Mapping of fields to common codewords A, B,
C and D codeword codeword field field width field bits bits A CRC
16 all 15:0 region ID 52 all 67:16 encoding format 2 all 69:68
region flags 6 all 75:70 macrodot size ID 4 all 79:76
[0345] When the region flags indicate that a particular codeword is
absent then the codeword is not coded in the tag pattern, i.e.
there are no macrodots representing the codeword. This applies to
the X and Y i.e. the X and Y codewords are present if the
<region is interactive> flag in the region flags is set.
4.10 Tag Imaging
[0346] The minimum imaging field of view required to guarantee
acquisition of data from an entire tag 4B has a diameter of 33.9s
(i.e. ((2.times.10)+4) 2s), allowing for arbitrary rotation and
translation of the surface coding in the field of view. Notably,
the imaging field of view does not have to be large enough to
guarantee capture of an entire tag--the arrangement of the data
symbols within each tag ensures that a any square portion of length
(l+4s) captures the requisite information in full, irrespective of
whether a whole tag is actually visible in the field-of-view. As
used herein, l is defined as the length of a tag.
[0347] In terms of imaging the coding pattern, the imaging
field-of-view is typically a circle. Accordingly, the imaging
field-of-view should preferably have diameter of at least (l+4s) 2
and less than two tag diameters. Importantly, the field-of-view is
not required to be at least two tag diameters, in contrast with
prior art tag designs, because it is not essential to capture an
entire tag 4B in the field of view.
[0348] The extra four macrodot units ensure that pulse-position
modulated values can be decoded from spatially coherent samples.
Furthermore, the extra four macrodot units ensure that all
requisite data symbols 304B can be read with each interaction.
These include the coordinate symbols from a column or row of a tag
(see Section 4.6.2) having a width of 3s.
[0349] In the present context, a "tag diameter" is given to mean
the length of a tag diagonal.
[0350] Given a maximum macrodot spacing of 169 microns, this gives
a required field of view of 5.74 mm.
[0351] Thus, a field of view of at least 5.93 mm (see Section 3.10)
is sufficient to capture data from an entire tag 4A from the first
position-coding pattern or an entire tag 4B from the second
position-coding pattern. Self-evidently, the requisite field of
view for capturing either tag 4A or tag 4B will vary depending on
the macrodot spacing in either the first or second position coding
patterns. This, in turn, depends on the print resolution of a
printer used to print the respective position-coding pattern.
4.11 Tag Decoding
[0352] FIG. 22 shows a tag image processing and decoding process
flow up to the stage of sampling registration symbols and decoding
the translation codewords. Firstly, a raw image 802 of the tag
pattern is acquired (at 800), for example via an image sensor such
as a CCD image sensor, CMOS image sensor, or a scanning laser and
photodiode image sensor. The raw image 802 is then typically
enhanced (at 804) to produce an enhanced image 806 with improved
contrast and more uniform pixel intensities. Image enhancement may
include global or local range expansion, equalization, and the
like. The enhanced image 806 is then typically filtered (at 808) to
produce a filtered image 810. Image filtering may consist of
low-pass filtering, with the low-pass filter kernel size tuned to
obscure macrodots 302 but to preserve targets 301. The filtering
step 808 may include additional filtering (such as edge detection)
to enhance target features 301. Encoding of data symbols 304 using
pulse position modulation (PPM) provides a more uniform coding
pattern 3 than simple binary dot encoding (as described in, for
example, U.S. Pat. No. 6,832,717). Advantageously, this helps
separate targets 301 from data areas, thereby allowing more
effective low-pass filtering of the PPM-encoded data compared to
binary-coded data.
[0353] Following low-pass filtering, the filtered image 810 is then
processed (at 812) to locate the targets 301. This may consist of a
search for target features whose spatial inter-relationship is
consistent with the known geometry of the tag pattern (i.e. targets
positioned at the corners of square cells). Candidate targets may
be identified directly from maxima in the filtered image 810, or
may be the subject of further characterization and matching, such
as via their (binary or grayscale) shape moments (typically
computed from pixels in the enhanced image 806 based on local
maxima in the filtered image 810), as described in U.S. Pat. No.
7,055,739, the contents of which is herein incorporated by
reference.
[0354] The identified targets 301 are then assigned (at 816) to a
target grid 818. Each cell of the grid 818 contains a symbol group
303, and several symbol groups will of course be visible in the
image. At this stage, individual tags 4 will not be identifiable in
the target grid 818, since the targets 301 do not themselves
demarcate one tag from another.
[0355] To allow macrodot values to be sampled accurately, the
perspective transform of the captured image must be inferred. Four
of the targets 301 are taken to be the perspective-distorted
corners of a square of known size in tag space, and the
eight-degree-of-freedom perspective transform 822 is inferred (at
820), based on solving the well-understood equations relating the
four tag-space and image-space point pairs. Calculation of the 2D
perspective transform is described in detail in, for example,
Applicant's U.S. Pat. No. 6,832,717, the contents of which is
herein incorporated by reference.
[0356] Since each image of either the first or second
position-coding pattern will typically contain at least 9 targets
arranged in a square grid, the accuracy of calculating the 2D
perspective transform is improved compared to the Applicant's
previous tag designs described in, for example, U.S. Pat. No.
6,832,717. Hence, more accurate position calculation can be
achieved with the tag design of the present invention.
[0357] The inferred tag-space to image-space perspective transform
822 is used to project each known macrodot position in tag space
into image space. Since all bits in the tags are represented by
PPM-encoding, the presence or absence of each macrodot 302 can be
determined using a local intensity reference, rather than a
separate intensity reference. Thus, PPM-encoding provides improved
data sampling compared with pure binary encoding.
[0358] The next stage determines a type of position-coding pattern
being imaged by the pen 400 from a translation codeword. In other
words, this stage distinguishes the first position-coding pattern
from the second position-coding pattern for subsequent sampling and
decoding.
[0359] Two or more orthogonal registration symbols (`VRS` and
`HRS`) are sampled (at 824), to allow decoding of the orthogonal
translation codewords and the orthogonal direction codewords. A
flag symbol value may also be decoded subsequently from the decoded
registration symbols.
[0360] Decoding of the orthogonal translation codewords (at 828)
yields either a (0, 1, 2) translation codeword or a (3, 4)
translation codeword (at 830).
[0361] Referring now to FIG. 23, the (0, 1, 2) translation codeword
indicates nine symbol groups per tag, thereby identifying (at 832A)
the imaged position-coding pattern as being the first
position-coding pattern ("Yarrow") containing tags 4A.
Alternatively, the (3, 4) translation codeword indicates four
symbol groups per tag, thereby identifying (at 832B) the imaged
position-coding pattern as being the second position-coding pattern
("Saffron") containing tags 4B.
[0362] Once the position-coding pattern has been identified at 832A
or 832B, subsequent sampling and decoding proceeds in accordance
with the position-coding pattern thus identified. Accordingly, the
decoded orthogonal translation codewords are used to determine the
translation of tags(s) in the field of view relative to the target
grid 818. This enables alignment of the tags 4A or 4B with the
target grid 818, thereby allowing individual tag(s), or portions
thereof, to be distinguished in the coding pattern 3 in the field
of view. In the case of the first position-coding pattern, the tags
4A (each containing nine symbol groups) are aligned (at 834A) with
the target grid 818. In the case of the second position-coding
pattern, the tags 4B (each containing four symbol groups) are
aligned (at 834B) with the target grid 818.
[0363] Since each symbol group 303 contains orthogonal registration
symbols, multiple translation codes can be decoded to provide
robust translation determination. As described in Sections 3.6.1
and 4.6.1, the translation code is a cyclic position code. Since
each row and each column of a tag contains M symbol groups, the
code has minimum distance M.times.M. This allows robust
determination of the alignment of tags 4A or 4B with the target
grid 818. The alignment needs to be both robust and accurate since
there are many possible alignments when each tag contains multiple
symbol groups 303.
[0364] After the translation of symbol groups 303 relative to tags
4A or 4B has been determined, then at least two orthogonal
direction codes are decoded (at 836A or 836B) to provide the
orientation 838A or 838B. As described in Sections 3.6.1 and 4.6.1,
since N vertical registration symbols in a tag form a vertical
direction code with minimum distance N, the vertical direction code
is capable of correcting (N-1)/2 errors. The horizontal direction
code is similarly capable of correcting (N-1)/2 errors using N
horizontal registration symbols. Hence, orientation determination
is very robust and capable of correcting errors, depending on the
number of registration symbols sampled.
[0365] Once initial imaging and decoding has yielded the 2D
perspective transform, the orientation, and the translation of
tag(s) relative to the target grid, the data codewords can then be
sampled and decoded (at 840A or 840B) to yield the requisite
decoded codewords 842A or 842B.
[0366] Decoding of data codewords in the first position-coding
pattern ("Yarrow") typically proceeds as follows: [0367] sample and
decode Reed-Solomon codeword containing encoding format etc. (A)
[0368] determine encoding format, and reject unknown encoding
[0369] on decode error flag bad region ID sample [0370] determine
region ID Reed-Solomon codeword format from region flags [0371]
sample and decode Reed-Solomon codeword containing region ID (B, C
and D) [0372] verify CRC of region ID [0373] on decode error flag
bad region ID sample [0374] determine region ID determine x and y
coordinate Reed-Solomon codeword format from region flags [0375]
sample and decode x and y coordinate Reed-Solomon codewords (X and
Y) [0376] determine tag x-y location from codewords [0377]
determine nib x-y location from tag x-y location and perspective
transform taking into account macrodot size (from macrodot size ID)
[0378] decode four or more flag symbols to determine active area
flag [0379] determine active area status of nib location with
reference to active area flag [0380] encode region ID, nib x-y
location, and nib active area status in digital ink ("interaction
data")
[0381] Decoding of data codewords in the second position-coding
pattern ("Saffron") typically proceeds as follows: [0382] sample
and decode common Reed-Solomon codeword (A) [0383] determine
encoding format, and reject unknown encoding [0384] on decode error
flag bad format sample [0385] determine region ID Reed-Solomon
codeword format from region flags [0386] verify CRC of region ID
[0387] on decode error flag bad region ID sample [0388] determine
region ID sample and decode x and y coordinate Reed-Solomon
codewords (X and Y) [0389] determine tag x-y location from
codewords [0390] determine nib x-y location from tag x-y location
and perspective transform taking into account macrodot size (from
macrodot size ID) [0391] encode region ID and nib x-y location in
digital ink ("interaction data")
[0392] In practice, when decoding a sequence of images of a tag
pattern, it is useful to exploit inter-frame coherence to obtain
greater effective redundancy.
[0393] Region ID decoding need not occur at the same rate as
position decoding.
[0394] The skilled person will appreciate that the decoding
sequence described above represents one embodiment of the present
invention. It will, of course, be appreciated that the interaction
data sent from the pen 400 to the netpage system may include other
data e.g. digital signature (see Section 3.9.4), pen mode (see US
2007/125860 incorporated herein by reference), orientation data,
force data, pen ID, nib ID etc.
[0395] An example of interpreting interaction data, received by the
netpage system from the netpage pen 400, is discussed briefly above
in Section 1. A more detailed discussion of how the netpage system
may interpret interaction data can be found in the Applicant's
previously-filed applications (see, for example, US 2007/130117 and
US 2007/108285, the contents of which are herein incorporated by
reference).
5. Netpage Pen
5.1 Functional Overview
[0396] The active sensing device (or "reader") of the netpage
system may take the form of a clicker (for clicking on a specific
position on a surface), a pointer having a stylus (for pointing or
gesturing on a surface using pointer strokes), or a pen having a
marking nib (for marking a surface with ink when pointing,
gesturing or writing on the surface). For a description of various
netpage readers, reference is made to U.S. Pat. No. 7,105,753; U.S.
Pat. No. 7,015,901; U.S. Pat. No. 7,091,960; and US Publication No.
2006/0028459, the contents of each of which are herein incorporated
by reference.
[0397] It will be appreciated that the present invention may
utilize any suitable optical reader. However, the Netpage pen 400
will be described herein as one such example.
[0398] In accordance with the present invention, either the first
position-coding pattern (as described in Section 3) or the second
position-coding pattern (as described in Section 4) may be read
using the same Netpage pen 400 using the image processing and
decoding steps described in Section 4.11.
[0399] The Netpage pen 400 is a motion-sensing writing instrument
which works in conjunction with a tagged Netpage surface containing
either the first or second position-coding patterns. The pen 400
incorporates a conventional ballpoint pen cartridge for marking the
surface, an image sensor and processor for simultaneously capturing
the absolute path of the pen on the surface and identifying the
surface, a force sensor for simultaneously measuring the force
exerted on the nib, and a real-time clock for simultaneously
measuring the passage of time.
[0400] While in contact with a tagged surface, as indicated by the
force sensor, the pen continuously images the surface region
adjacent to the nib, and decodes the nearest tag in its field of
view to determine both the identity of the surface, its own
instantaneous position on the surface and the pose of the pen. The
pen thus generates a stream of timestamped position samples
relative to a particular surface, and transmits this stream to the
Netpage server 10. The sample stream describes a series of strokes,
and is conventionally referred to as digital ink (DInk). Each
stroke is delimited by a pen down and a pen up event, as detected
by the force sensor. More generally, any data resulting from an
interaction with a Netpage, and transmitted to the Netpage server
10, is referred to herein as "interaction data".
[0401] The pen samples its position at a sufficiently high rate
(nominally 100 Hz) to allow a Netpage server to accurately
reproduce hand-drawn strokes, recognise handwritten text, and
verify hand-written signatures.
[0402] The Netpage pen also supports hover mode in interactive
applications. In hover mode the pen is not in contact with the
paper and may be some small distance above the surface of the paper
(or other substrate). This allows the position of the pen,
including its height and pose to be reported. In the case of an
interactive application the hover mode behaviour can be used to
move a cursor without marking the paper, or the distance of the nib
from the coded surface could be used for tool behaviour control,
for example an air brush function.
[0403] The pen includes a Bluetooth radio transceiver for
transmitting digital ink via a relay device to a Netpage server.
When operating offline from a Netpage server the pen buffers
captured digital ink in non-volatile memory. When operating online
to a Netpage server the pen transmits digital ink in real time.
[0404] The pen is supplied with a docking cradle or "pod". The pod
contains a Bluetooth to USB relay. The pod is connected via a USB
cable to a computer which provides communications support for local
applications and access to Netpage services.
[0405] The pen is powered by a rechargeable battery. The battery is
not accessible to or replaceable by the user. Power to charge the
pen can be taken from the USB connection or from an external power
adapter through the pod. The pen also has a power and
USB-compatible data socket to allow it to be externally connected
and powered while in use.
[0406] The pen cap serves the dual purpose of protecting the nib
and the imaging optics when the cap is fitted and signalling the
pen to leave a power-preserving state when uncapped.
5.2 Ergonomics and Layout
[0407] FIG. 24 shows a rounded triangular profile giving the pen
400 an ergonomically comfortable shape to grip and use the pen in
the correct functional orientation. It is also a practical shape
for accommodating the internal components. A normal pen-like grip
naturally conforms to a triangular shape between thumb 402, index
finger 404 and middle finger 406.
[0408] As shown in FIG. 25, a typical user writes with the pen 400
at a nominal pitch of about 30 degrees from the normal toward the
hand 408 when held (positive angle) but seldom operates a pen at
more than about 10 degrees of negative pitch (away from the hand).
The range of pitch angles over which the pen 400 is able to image
the pattern on the paper has been optimised for this asymmetric
usage. The shape of the pen 400 helps to orient the pen correctly
in the user's hand 408 and to discourage the user from using the
pen "upside-down". The pen functions "upside-down" but the
allowable tilt angle range is reduced.
[0409] The cap 410 is designed to fit over the top end of the pen
400, allowing it to be securely stowed while the pen is in use.
Multi colour LEDs illuminate a status window 412 in the top edge
(as in the apex of the rounded triangular cross section) of the pen
400 near its top end. The status window 412 remains un-obscured
when the cap is stowed. A vibration motor is also included in the
pen as a haptic feedback system (described in detail below).
[0410] As shown in FIG. 26, the grip portion of the pen has a
hollow chassis molding 416 enclosed by a base molding 528 to house
the other components. The ink cartridge 414 for the ball point nib
(not shown) fits naturally into the apex 420 of the triangular
cross section, placing it consistently with the user's grip. This
in turn provides space for the main PCB 422 in the centre of the
pen and for the battery 424 in the base of the pen. By referring to
FIG. 27A, it can be seen that this also naturally places the
tag-sensing optics 426 unobtrusively below the nib 418 (with
respect to nominal pitch). The nib molding 428 of the pen 400 is
swept back below the ink cartridge 414 to prevent contact between
the nib molding 428 and the paper surface when the pen is operated
at maximum pitch.
[0411] As best shown in FIG. 27B, the imaging field of view 430
emerges through a centrally positioned IR filter/window 432 below
the nib 418, and two near-infrared illumination LEDs 434, 436
emerge from the two bottom corners of the nib molding 428. Each LED
434, 436 has a corresponding illumination field 438, 440.
[0412] As the pen is hand-held, it may be held at an angle that
causes reflections from one of the LED's that are detrimental to
the image sensor. By providing more than one LED, the LED causing
the offending reflections can be extinguished.
[0413] Specific details of the pen mechanical design can be found
in US Publication No. 2006/0028459, the contents of which are
herein incorporated by reference.
5.3 Pen Feedback Indications
[0414] FIG. 28 is a longitudinal cross section through the
centre-line if the pen 400 (with the cap 410 stowed on the end of
the pen). The pen incorporates red and green LEDs 444 to indicate
several states, using colours and intensity modulation. A light
pipe 448 on the LEDs 444 transmit the signal to the status
indicator window 412 in the tube molding 416. These signal status
information to the user including power-on, battery level,
untransmitted digital ink, network connection on-line, fault or
error with an action, detection of an "active area" flag, detection
of an "embedded data" flag, further data sampling to required to
acquire embedded data, acquisition of embedded data completed
etc.
[0415] A vibration motor 446 is used to haptically convey
information to the user for important verification functions during
transactions. This system is used for important interactive
indications that might be missed due to inattention to the LED
indicators 444 or high levels of ambient light. The haptic system
indicates to the user when: [0416] The pen wakes from standby mode
[0417] There is an error with an action [0418] To acknowledge a
transaction
5.4 Pen Optics
[0419] The pen incorporates a fixed-focus narrowband infrared
imaging system. It utilizes a camera with a short exposure time,
small aperture, and bright synchronised illumination to capture
sharp images unaffected by defocus blur or motion blur.
TABLE-US-00017 TABLE 16 Optical Specifications Magnification
.sup.~0.225 Focal length of 6.0 mm lens Viewing distance 30.5 mm
Total track length 41.0 mm Aperture diameter 0.8 mm Depth of field
6.5 mm Exposure time 200 us Wavelength 810 nm Image sensor size 140
.times. 140 pixels Pixel size 10 um Pitch range .sup.~15 to. 45 deg
Roll range .sup.~30 to. 30 deg Yaw range 0 to 360 deg Minimum
sampling 2.25 pixels per rate macrodot Maximum pen 0.5 m/s velocity
.sup.1Allowing 70 micron blur radius .sup.2Illumination and filter
.sup.3Pitch, roll and yaw are relative to the axis of the pen
[0420] Cross sections showing the pen optics are provided in FIGS.
29A and 29B. An image of the Netpage tags printed on a surface 548
adjacent to the nib 418 is focused by a lens 488 onto the active
region of an image sensor 490. A small aperture 494 ensures the
available depth of field accommodates the required pitch and roll
ranges of the pen 400.
[0421] First and second LEDs 434 and 436 brightly illuminate the
surface 549 within the field of view 430. The spectral emission
peak of the LEDs is matched to the spectral absorption peak of the
infrared ink used to print Netpage tags to maximise contrast in
captured images of tags. The brightness of the LEDs is matched to
the small aperture size and short exposure time required to
minimise defocus and motion blur.
[0422] A longpass IR filter 432 suppresses the response of the
image sensor 490 to any coloured graphics or text spatially
coincident with imaged tags and any ambient illumination below the
cut-off wavelength of the filter 432. The transmission of the
filter 432 is matched to the spectral absorption peak of the
infrared ink to maximise contrast in captured images of tags. The
filter also acts as a robust physical window, preventing
contaminants from entering the optical assembly 470.
5.5 Pen Imaging System
[0423] A ray trace of the optic path is shown in FIG. 30. The image
sensor 490 is a CMOS image sensor with an active region of 140
pixels squared. Each pixel is 10 .mu.m squared, with a fill factor
of 93%. Turning to FIG. 31, the lens 488 is shown in detail. The
dimensions are: [0424] D=3 mm [0425] R1=3.593 mm [0426] R2=15.0 mm
[0427] X=0.8246 mm [0428] Y=1.0 mm [0429] Z=0.25 mm
[0430] This gives a focal length of 6.15 mm and transfers the image
from the object plane (tagged surface 548) to the image plane
(image sensor 490) with the correct sampling frequency to
successfully decode all images over the specified pitch, roll and
yaw ranges. The lens 488 is biconvex, with the most curved surface
facing the image sensor. The minimum imaging field of view 430
required to guarantee acquisition of sufficient tag data with each
interaction is dependent on the specific coding pattern. The
required field of view for the coding patterns of the present
invention is described in Section 4.10.
[0431] The required paraxial magnification of the optical system is
defined by the minimum spatial sampling frequency of 2.25 pixels
per macrodot for the fully specified tilt range of the pen 400, for
the image sensor 490 of 10 .mu.m pixels. Typically, the imaging
system employs a paraxial magnification of 0.225, the ratio of the
diameter of the inverted image at the image sensor to the diameter
of the field of view at the object plane, on an image sensor 490 of
minimum 128.times.128 pixels. The image sensor 490 however is
140.times.140 pixels, in order to accommodate manufacturing
tolerances. This allows up to +/-120 .mu.m (12 pixels in each
direction in the plane of the image sensor) of misalignment between
the optical axis and the image sensor axis without losing any of
the information in the field of view.
[0432] The lens 488 is made from Poly-methyl-methacrylate (PMMA),
typically used for injection moulded optical components. PMMA is
scratch resistant, and has a refractive index of 1.49, with 90%
transmission at 810 nm. The lens is biconvex to assist moulding
precision and features a mounting surface to precisely mate the
lens with the optical barrel molding 492.
[0433] A 0.8 mm diameter aperture 494 is used to provide the depth
of field requirements of the design.
[0434] The specified tilt range of the pen is 15.0 to 45.0 degree
pitch, with a roll range of 30.0 to 30.0 degrees. Tilting the pen
through its specified range moves the tilted object plane up to 6.3
mm away from the focal plane. The specified aperture thus provides
a corresponding depth of field of 6.5 mm, with an acceptable blur
radius at the image sensor of 16 .mu.m.
[0435] Due to the geometry of the pen design, the pen operates
correctly over a pitch range of 33.0 to 45.0 degrees.
[0436] Referring to FIG. 32, the optical axis 550 is pitched 0.8
degrees away from the nib axis 552. The optical axis and the nib
axis converge toward the paper surface 548. With the nib axis 552
perpendicular to the paper, the distance A between the edge of the
field of view 430 closest to the nib axis and the nib axis itself
is 1.2 mm.
[0437] The longpass IR filter 432 is made of CR-39, a lightweight
thermoset plastic heavily resistant to abrasion and chemicals such
as acetone. Because of these properties, the filter also serves as
a window. The filter is 1.5 mm thick, with a refractive index of
1.50. Each filter may be easily cut from a large sheet using a
CO.sub.2 laser cutter.
5.6 Electronics Design
TABLE-US-00018 [0438] TABLE 17 Electrical Specifications Processor
ARM7 (Atmel AT91FR40162) running at 80 MHz with 256 kB SRAM and 2
MB flash memory Digital ink storage 5 hours of writing capacity
Bluetooth 1.2 Compliance USB Compliance 1.1 Battery standby 12
hours (cap off), >4 weeks (cap on) time Battery writing 4 hours
of cursive writing (81% pen down, time assuming easy offload of
digital ink) Battery charging 2 hours time Battery Life Typically
300 charging cycles or 2 years (whichever occurs first) to 80% of
initial capacity. Battery ~340 mAh at 3.7 V, Lithium-ion Polymer
Capacity/Type (LiPo)
[0439] FIG. 33 is a block diagram of the pen electronics. The
electronics design for the pen is based around five main sections.
These are: [0440] the main ARM7 microprocessor 574, [0441] the
image sensor and image processor 576, [0442] the Bluetooth
communications module 578, [0443] the power management unit IC
(PMU) 580 and [0444] the force sensor microprocessor 582.
5.6.1 Microprocessor
[0445] The pen uses an Atmel AT91FR40162 microprocessor (see Atmel,
AT91 ARM Thumb Microcontrollers--A T91FR40162 Preliminary,
http://www.keil.com/dd/docs/datashts/atmel/at91fr40162.pdf) running
at 80 MHz. The AT91FR40162 incorporates an ARM7 microprocessor, 256
kBytes of on-chip single wait state SRAM and 2 MBytes of external
flash memory in a stack chip package.
[0446] This microprocessor 574 forms the core of the pen 400. Its
duties include: [0447] setting up the Jupiter image sensor 584,
[0448] decoding images of Netpage coding pattern (see Section
4.11), with assistance from the image processing features of the
image sensor 584, for inclusion in the digital ink stream along
with force sensor data received from the force sensor
microprocessor 582, [0449] setting up the power management IC (PMU)
580, [0450] compressing and sending digital ink via the Bluetooth
communications module 578, and [0451] programming the force sensor
microprocessor 582.
[0452] The ARM7 microprocessor 574 runs from an 80 MHz oscillator.
It communicates with the Jupiter image sensor 576 using a Universal
Synchronous Receiver Transmitter (USRT) 586 with a 40 MHz clock.
The ARM7 574 communicates with the Bluetooth module 578 using a
Universal Asynchronous Receiver Transmitter (UART) 588 running at
115.2 kbaud. Communications to the PMU 580 and the Force Sensor
microprocessor (FSP) 582 are performed using a Low Speed Serial bus
(LSS) 590. The LSS is implemented in software and uses two of the
microprocessor's general purpose IOs.
[0453] The ARM7 microprocessor 574 is programmed via its JTAG
port.
5.6.2 Image Sensor
[0454] The `Jupiter` Image Sensor 584 (see US Publication No.
2005/0024510, the contents of which are incorporated herein by
reference) contains a monochrome sensor array, an analogue to
digital converter (ADC), a frame store buffer, a simple image
processor and a phase lock loop (PLL). In the pen, Jupiter uses the
USRT's clock line and its internal PLL to generate all its clocking
requirements. Images captured by the sensor array are stored in the
frame store buffer. These images are decoded by the ARM7
microprocessor 574 with help from the `Callisto` image processor
contained in Jupiter. The Callisto image processor performs, inter
alia, low-pass filtering of captured images (see Section 4.11 and
US Publication No. 2005/0024510) before macrodot sampling and
decoding by the microprocessor 574.
[0455] Jupiter controls the strobing of two infrared LEDs 434 and
436 at the same time as its image array is exposed. One or other of
these two infrared LEDs may be turned off while the image array is
exposed to prevent specular reflection off the paper that can occur
at certain angles.
5.6.3 Bluetooth Communications Module
[0456] The pen uses a CSR BlueCore4-External device (see CSR,
BlueCore4-External Data Sheet rev c, 6 Sep. 2004) as the Bluetooth
controller 578. It requires an external 8 Mbit flash memory device
594 to hold its program code. The BlueCore4 meets the Bluetooth
v1.2 specification and is compliant to v0.9 of the Enhanced Data
Rate (EDR) specification which allows communication at up to 3
Mbps.
[0457] A 2.45 GHz chip antenna 486 is used on the pen for the
Bluetooth communications.
[0458] The BlueCore4 is capable of forming a UART to USB bridge.
This is used to allow USB communications via data/power socket 458
at the top of the pen 456.
[0459] Alternatives to Bluetooth include wireless LAN and PAN
standards such as IEEE 802.11 (Wi-Fi) (see IEEE, 802.11 Wireless
Local Area Networks,
http://grouper.ieee.org/groups/802/11/index.html), IEEE 802.15 (see
IEEE, 802.15 Working Groupfor WPAN,
http://grouper.ieee.org/groups/802/15/index.html), ZigBee (see
ZigBee Alliance, http://www.zigbee.org), and WirelessUSB Cypress
(see WirelessUSB LR 2.4-GHz DSSS Radio SoC,
http://www.cypress.com/cfuploads/img/products/cywusb6935.pdf), as
well as mobile standards such as GSM (see GSM Association,
http://www.gsmworld.com/index.shtml), GPRS/EDGE, GPRSPlatform,
http://www.gsmworld.com/technology/gprs/index.shtml), CDMA (see
CDMA Development Group, http://www.cdg.org/, and Qualcomm,
http://www.qualcomm.com), and UMTS (see 3rd Generation Partnership
Project (3GPP), http://www.3gpp.org).
5.6.4 Power Management Chip
[0460] The pen uses an Austria Microsystems AS3603 PMU 580 (see
Austria Microsystems, AS3603 Multi-Standard Power Management Unit
Data Sheet v2.0). The PMU is used for battery management, voltage
generation, power up reset generation and driving indicator LEDs
and the vibrator motor.
[0461] The PMU 580 communicates with the ARM7 microprocessor 574
via the LSS bus 590.
5.6.5 Force Sensor Subsystem
[0462] The force sensor subsystem comprises a custom Hokuriku force
sensor 500 (based on Hokuriku, HFD-500 Force Sensor,
http://www.hdk.cojp/pdf/eng/e1381AA.pdf), an amplifier and low pass
filter 600 implemented using op-amps and a force sensor
microprocessor 582.
[0463] The pen uses a Silicon Laboratories C8051F330 as the force
sensor microprocessor 582 (see Silicon Laboratories, C8051F330/1
MCUData Sheet, rev 1.1). The C8051F330 is an 8051 microprocessor
with on chip flash memory, 10 bit ADC and 10 bit DAC. It contains
an internal 24.5 MHz oscillator and also uses an external 32.768
kHz tuning fork.
[0464] The Hokuriku force sensor 500 is a silicon piezoresistive
bridge sensor. An op-amp stage 600 amplifies and low pass
(anti-alias) filters the force sensor output. This signal is then
sampled by the force sensor microprocessor 582 at 5 kHz.
[0465] Alternatives to piezoresistive force sensing include
capacitive and inductive force sensing (see Wacom, "Variable
capacity condenser and pointer", US Patent Application 20010038384,
filed 8 Nov. 2001, and Wacom, Technology,
http://www.wacom-components.com/english/tech.asp).
[0466] The force sensor microprocessor 582 performs further
(digital) filtering of the force signal and produces the force
sensor values for the digital ink stream. A frame sync signal from
the Jupiter image sensor 576 is used to trigger the generation of
each force sample for the digital ink stream. The temperature is
measured via the force sensor microprocessor's 582 on chip
temperature sensor and this is used to compensate for the
temperature dependence of the force sensor and amplifier. The
offset of the force signal is dynamically controlled by input of
the microprocessor's DAC output into the amplifier stage 600.
[0467] The force sensor microprocessor 582 communicates with the
ARM7 microprocessor 574 via the LSS bus 590. There are two separate
interrupt lines from the force sensor microprocessor 582 to the
ARM7 microprocessor 574. One is used to indicate that a force
sensor sample is ready for reading and the other to indicate that a
pen down/up event has occurred.
[0468] The force sensor microprocessor flash memory is programmed
in-circuit by the ARM7 microprocessor 574.
[0469] The force sensor microprocessor 582 also provides the real
time clock functionality for the pen 400. The RTC function is
performed in one of the microprocessor's counter timers and runs
from the external 32.768 kHz tuning fork. As a result, the force
sensor microprocessor needs to remain on when the cap 472 is on and
the ARM7 574 is powered down. Hence the force sensor microprocessor
582 uses a low power LDO separate from the PMU 580 as its power
source. The real time clock functionality includes an interrupt
which can be programmed to power up the ARM7 574.
[0470] The cap switch 602 is monitored by the force sensor
microprocessor 582. When the cap assembly 472 is taken off (or
there is a real time clock interrupt), the force sensor
microprocessor 582 starts up the ARM7 572 by initiating a power on
and reset cycle in the PMU 580.
5.7 Pen Software
[0471] The Netpage pen software comprises that software running on
microprocessors in the Netpage pen 400 and Netpage pod.
[0472] The pen contains a number of microprocessors, as detailed in
Section 5.6. The Netpage pen software includes software running on
the Atmel ARM7 CPU 574 (hereafter CPU), the Force Sensor
microprocessor 582, and also software running in the VM on the CSR
BlueCore Bluetooth module 578 (hereafter pen BlueCore). Each of
these processors has an associated flash memory which stores the
processor specific software, together with settings and other
persistent data. The pen BlueCore 578 also runs firmware supplied
by the module manufacturer, and this firmware is not considered a
part of the Netpage pen software.
[0473] The pod contains a CSR BlueCore Bluetooth module (hereafter
pod BlueCore). The Netpage pen software also includes software
running in the VM on the pod BlueCore.
[0474] As the Netpage pen 400 traverses a Netpage tagged surface
548, a stream of correlated position and force samples are
produced. This stream is referred to as DInk. Note that DInk may
include samples with zero force (so called "Hover DInk") produced
when the Netpage pen is in proximity to, but not marking, a Netpage
tagged surface.
[0475] The CPU component of the Netpage pen software is responsible
for DInk capture, tag image processing and decoding (in conjunction
with the Jupiter image sensor 576), storage and offload management,
host communications, user feedback and software upgrade. It
includes an operating system (RTOS) and relevant hardware drivers.
In addition, it provides a manufacturing and maintenance mode for
calibration, configuration or detailed (non-field) fault diagnosis.
The Force Sensor microprocessor 582 component of the Netpage pen
software is responsible for filtering and preparing force samples
for the main CPU. The pen BlueCore VM software is responsible for
bridging the CPU UART 588 interface to USB when the pen is
operating in tethered mode. The pen BlueCore VM software is not
used when the pen is operating in Bluetooth mode.
[0476] The pod BlueCore VM software is responsible for sensing when
the pod is charging a pen 400, controlling the pod LEDs
appropriately, and communicating with the host PC via USB.
[0477] For a detailed description of the software modules,
reference is made to US Publication No. 2006/0028459, the contents
of which are herein incorporated by reference.
[0478] The present invention has been described with reference to a
preferred embodiment and number of specific alternative
embodiments. However, it will be appreciated by those skilled in
the relevant fields that a number of other embodiments, differing
from those specifically described, will also fall within the spirit
and scope of the present invention. Accordingly, it will be
understood that the invention is not intended to be limited to the
specific embodiments described in the present specification,
including documents incorporated by cross-reference as appropriate.
The scope of the invention is only limited by the attached
claims.
* * * * *
References