U.S. patent number RE40,466 [Application Number 11/006,471] was granted by the patent office on 2008-08-26 for method for organizing and compressing spatial data.
This patent grant is currently assigned to Tierravision, Inc.. Invention is credited to Alfred M. Wallner.
United States Patent |
RE40,466 |
Wallner |
August 26, 2008 |
Method for organizing and compressing spatial data
Abstract
A method for organizing and compressing spatial data to enable
fast, incremental downloads of spatial data over a network. The
method comprises multiple steps for segmenting and reducing spatial
data, and introduces a location-relevant naming system for storing
and accessing the data. Applications installed on remote devices
are able to efficiently compute data file names based solely on
location information, download the data over a network and cache
the data on the device.
Inventors: |
Wallner; Alfred M. (San Diego,
CA) |
Assignee: |
Tierravision, Inc. (San Diego,
CA)
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Family
ID: |
31888568 |
Appl.
No.: |
11/006,471 |
Filed: |
December 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09668695 |
Sep 22, 2000 |
06703947 |
Mar 9, 2004 |
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Current U.S.
Class: |
341/50 |
Current CPC
Class: |
H03M
7/30 (20130101) |
Current International
Class: |
H03M
7/00 (20060101) |
Field of
Search: |
;341/50,51,87
;342/356,357.01,357.02,357.03 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Young; Brian
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear
LLP
Claims
What is claimed is:
1. A method for organizing spatial data comprising the steps of: a)
parsing the spatial data into a plurality of packets; b) segmenting
the packets; c) reducing a size of the packets by eliminating at
least one data point from at least one display element by applying
an angle comparison between an adjacent display element, wherein
the at least one data point is eliminated if an angle between the
at least one display element and the adjacent display element is
about 180.degree.; and d) generating a name for each of the
packets.
2. The method of claim 1, wherein the spatial data comprises
topographic information comprising a plurality of elements
containing geodetic coordinates.
3. The method of claim 1, wherein the step of parsing the spatial
data comprises: selecting at least one entity within the data, the
entity selected from a group consisting of: a road, a railway, an
airport, a river, a lake, a shore line, a park, an entity
comprising a geometric shape, and an entity comprising a
substantially rectangular shape.
4. The method of claim 1, wherein the step of parsing the spatial
data comprises: generating a substantially rectangular element
comprising about 1.degree. longitude and about 1/2.degree.
latitude.
5. The method of claim 1, wherein the step of parsing the spatial
data comprises: separating a topographic element from an attribute
element; wherein the topographic element comprises elements
expressed using a geodetic coordinate system; and the attribute
element is related to the topographic element.
6. The method of claim 1, wherein the step of segmenting the
packets comprises: dividing the packets into at least one element,
the element selected from a group consisting of: an 8.times.8 grid,
a 64.times.64 grid, a substantially rectangular grid comprising
about 1.degree. longitude and about 1/2.degree. latitude, and a
substantially rectangular grid comprising about 1/8.degree.
longitude and about 1/16.degree. latitude.
7. The method of claim 1, wherein the step of reducing the size of
the segmented packets comprises: eliminating elements selected from
a group consisting of: a polygon, a lake, a geographic area, a
topographic element and an attribute element.
8. The method of claim 1, wherein the step of reducing the size of
the segmented packets comprises: eliminating a plurality of data
points from a topographic element.
9. The method of claim 1, wherein the step of reducing the size of
the segmented packets comprises: transforming a geodetic coordinate
from a real number to an integer number, wherein the integer number
ranges from about 0 to about 65535.
10. The method of claim 1, wherein the step of reducing the size of
the segmented packets comprises: eliminating a plurality of data
points from at least one topographic element by applying an angle
comparison between an adjacent topographic element line, wherein at
least one data point is eliminated if an angle between the at least
one topographic element and the adjacent topographic element line
is about 180.degree..
11. The method of claim 1, wherein the step of generating the name
for each of the packets comprises the step of generating a
location-relevant naming system.
12. The method of claim 1, wherein the step of generating the name
for each of the packets comprises the step of generating a
location-relevant naming system, wherein the packet name comprises
location information representing an offset from an earth
origin.
13. The method of claim 12, wherein the earth origin is selected
from a group consisting of: a North Pole, and a location other than
the North Pole.
14. The method of claim 1, further including the step of: repeating
any one of steps a, b, c and d to process an entire spatial
database.
15. A method .[.for.]. .Iadd.of .Iaddend.displaying a map, the
method comprising .[.the steps of.]. : obtaining information
relating to a location; calculating at least one packet name;
determining a data level .Iadd.associated with at least one packet,
wherein calculating the packet name is based at least partly on the
data level.Iaddend.; displaying the map; and caching .Iadd.the
.Iaddend.at least one packet until an amount of computer storage
space is filled, and determining which packets should be
replaced.
16. The method of claim 15, wherein the step of calculating the at
least one packet name comprises: computing the at least one data
packet name using a geodetic coordinate.
17. The method of claim 15, wherein the step of calculating the at
least one packet name comprises: calculating a request location;
and using the request location to calculate the at least one packet
name.
18. .[.The method of claim 15,.]. .Iadd.A method of displaying a
map, the method comprising: obtaining information relating to a
location; calculating at least one packet name; determining a data
level; displaying the map; caching at least one packet until an
amount of computer storage space is filled; and determining which
packets should be replaced,.Iaddend. wherein .[.the step of.].
calculating the at least one packet name comprises: computing four
adjacent data packet names; fetching the packets from a server; and
combining an information contained in the packets to generate a
map.
19. .[.The method of claim 15,.]. .Iadd.A method of displaying a
map, the method comprising: obtaining information relating to a
location; calculating at least one packet name; determining a data
level; displaying the map; caching at least one packet until an
amount of computer storage space is filled; and determining which
packets should be replaced,.Iaddend. wherein .[.the step of.].
determining the data level comprises: determining a resolution
level selected from a group consisting of: an address, a city, a
zip code and a building floor plan.
20. The method of claim 15, further including the step of: caching
at least one data packet until an amount of computer storage space
is filled, and determining which packets should be replaced.
21. The method of claim 15, further including the step of: checking
a local cache before requesting a data packet from a remote
device.
22. .[.A method.]. .Iadd.An apparatus .Iaddend.for organizing
spatial data comprising .[.the steps of.]. : a) means for parsing
the spatial data into a plurality of packets; b) means for
segmenting the packets; c) means for reducing a size of the packets
by eliminating at least one data point from at least one display
element by applying an angle comparison between an adjacent display
element, wherein the at least one data point is eliminated if an
angle between the at least one display element and the adjacent
display element is about 180.degree.; and d) means for generating a
name for each of the packets.
.Iadd.23. A method of digital map compression, comprising:
representing each data point of a digital map as a set of
geographic coordinates comprising a tuple of an offset and a value,
wherein the offset represents a corner of a given rectangle;
segmenting the digital map; and reducing the number of data points
in each segment of the digital map including calculating a new
offset and value according to predefined minimum and maximum
corners of a data segment..Iaddend.
.Iadd.24. The method of claim 23, wherein the offsets are
represented as two byte integers..Iaddend.
.Iadd.25. A system for digital map compression, comprising: means
for representing each data point of a digital map as a set of
geodetic coordinates comprising a tuple of an offset and a value,
wherein the offset represents a corner of a given rectangle; means
for segmenting the digital map; and means for reducing the number
of data points in each segment of the digital map including
calculating a new offset and value according to predefined minimum
and maximum corners of a data segment..Iaddend.
.Iadd.26. The system of claim 25, wherein the offsets are
represented as two byte integers..Iaddend.
.Iadd.27. A system for digital map compression, comprising: a
database configured to represent each data point of a digital map
as a set of geodetic coordinates comprising a tuple of an offset
and a value, wherein the offset represents a corner of a given
rectangle; a data segmentation module configured to segment the
digital map; and a data reduction module configured to reduce the
number of data points in each segment of the digital map including
calculating a new offset and value according to predefined minimum
and maximum corners of a data segment..Iaddend.
.Iadd.28. The system of claim 27, wherein the offsets are
represented as two byte integers..Iaddend.
.Iadd.29. A method of reducing data defining a map, the method
comprising: selecting a point from a plurality of points defining a
portion of the map; determining a first line from the point to a
first adjacent point of the plurality of points; determining a
second line from the point to a second adjacent point of the
plurality of points such that the first and second lines intersect
at the point; eliminating the point in dependence on whether an
angle formed between the first and second lines at the point
exceeds a threshold angle..Iaddend.
.Iadd.30. The method of claim 29, wherein selecting a point
comprises selecting every other adjacent point of the plurality of
points..Iaddend.
.Iadd.31. A method of reducing data defining a map, the method
comprising: transforming each of a plurality of points defining a
portion of the map into a plurality of offsets from a selected
point, wherein the portion of the map and the selected point are
selected such that at least one dimension of each of the plurality
of offsets is less than a predetermined value, wherein the
predetermined value is selected so that each of the plurality of
offsets is representable by less data than each of the
corresponding points..Iaddend.
.Iadd.32. The method of claim 31, wherein the selected point is
associated with an identifier of the portion..Iaddend.
.Iadd.33. The method of claim 31, wherein the portion defines a
region bounded by a shape and where the first point is associated
with a point of the shape..Iaddend.
.Iadd.34. The method of claim 33, wherein the selected point is
associated with a predetermined corner of the shape..Iaddend.
.Iadd.35. The method of claim 32, wherein the selected point is
encoded in a name of a data structure associated with the portion
of the map..Iaddend.
.Iadd.36. The method of claim 36, wherein the data structure
comprises a file..Iaddend.
.Iadd.37. The method of claim 31, wherein the predetermined value
is less than 65536..Iaddend.
.Iadd.38. The method of claim 31, wherein the predetermined value
is selected so that each of the plurality of offsets is
representable as a 16 bit value..Iaddend.
.Iadd.39. A method of providing a map, the method comprising:
receiving a request for information relating to a location;
determining a data level of the information; identifying a data
segment associated with the location and the data level, the data
segment comprising geographic coordinates that are indicative of
offsets from a coordinate; and determining at least one identifier
for a data segment indicative of the coordinate of the data
segment; and displaying the data segment based on the
coordinate..Iaddend.
.Iadd.40. The method of claim 39, further comprising: caching the
data segment based at least partly on the identifier..Iaddend.
.Iadd.41. The method of claim 39, wherein calculating the at least
one identifier is based at least partly on the data
level..Iaddend.
.Iadd.42. The method of claim 39, wherein the data segment is
indicative of map data in a region and wherein the coordinate
comprises a predetermined location in the region..Iaddend.
.Iadd.43. The method of claim 39, wherein the data segment is
indicative of map data in a rectangular region and wherein the
coordinate comprises at least one of an upper right, upper left,
lower right, or lower left corner of the rectangular
region..Iaddend.
.Iadd.44. The method of claim 39, wherein displaying the data
segment based on the coordinate comprises offsetting geographic
coordinates of the data segment from the coordinate..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of optimization of spatial
databases for functional purposes, and in particular to optimize
spatial data to achieve minimal download data size for use with
cartographic applications in a networked environment.
2. Discussion of Prior Art
A spatial database comprises topographic information in the form of
shapes, lines and points encoded with geodetic coordinates, as well
as sets of attributes further describing each form. Internet-based
applications use the spatial database to generate bitmap images
based on user input such as zip code or address on a server and
transmit the map images to client devices. Bitmap-based solutions
have numerous limitations, which are well known in the art. While
prior art describe systems, which transfer vector data to client
devices instead of bitmaps, bitmap solutions remain more efficient
in terms of data transfer overhead. The initial download size of
vector data is significant, and unless the user interacts
repeatedly with the map, the total data amount of vector data is
greater than the total data amount of bitmap images. Even if the
user interacts frequently with the map and the total download size
requirements for bitmap and vector data were about the same, most
users prefer to have a number of shorter download wait times rather
than one long download wait time. Therefore, except for a few
non-mainstream applications, bitmap-based solutions are widely used
in networked applications.
In navigation systems, a navigation application and spatial data
are packaged and supplied as a complete system on a non-volatile
storage medium. Said navigation systems may be installed in
vehicles or in standalone devices. These navigation systems rely on
significant computing resources such as powerful processors and
large permanent storage capacities. Prior art introduces solutions,
which use structuring and segmenting of spatial databases to
improve data access times and navigational functionality. Said
solutions are not applicable when computing resources are severely
limited, as encountered on personal digital assistants and
smartphones, on which one would want to have access to navigation
capabilities and maps. Even when said resources are made available
for car navigation systems, more powerful hardware results in
higher cost for the system. More importantly still, since spatial
data changes quite frequently, standalone car navigation systems
will inevitably start producing out-of-date navigation instructions
over time. It is therefore necessary to update the local database
from time to time. Improved methods for updating said local
databases have been introduced by prior art. Nevertheless, the
requirement to repeatedly update data used by navigation systems
remains a major inconvenience for both consumers as well as
navigation system suppliers. Suppliers face substantial costs for
creating and distributing the data in regular intervals, and any
errors discovered after storing data sets on non-volatile media are
costly to fix. To address the above problems, it is desirable to
keep frequently changing spatial data on a central server and use
wireless transmission networks to deliver navigation functionality
to remote devices. Navigational functions such as route calculation
and driving directions are performed on the server, making it also
easier to integrate real-time road traffic condition data. Driving
directions or maneuver instructions are text-based and relatively
small in terms of data size, allowing for fairly quick wireless
data transmission. On the other hand, the ability to provide
graphical, cartographic map display introduces much larger data
size overhead. Given the data transfer rates of wireless networks
presently and during several years to come, users would experience
unacceptably slow performance for map display functionality on
remote devices.
The objective of this invention is to introduce a new spatial
database system, which reduces the data size, makes it possible to
download data in small increments as needed, and which can be used
with applications such as navigation systems, for which
vector-based functionality is needed.
SUMMARY OF THE INVENTION
The primary object of the invention is to provide a compressed
spatial database system, which enables incremental and efficient
download of spatial vector data over a network. Another object of
the invention is to introduce a location-relevant naming system so
that software running on network client devices can efficiently
compute data segment file names depending on user interaction with
a map or device-supplied location data (e.g. GPS). A third object
of the invention is to enable combined online and offline operation
capability of a digital map display system. Another object of the
invention is to provide server-independent map display capability
based on GPS location input. A further object of the invention is
to introduce a system allowing updating of dynamic location content
without having to retransmit redundant map data. Yet another object
of the invention is to enable map centering despite using a
segmented data system.
Other objects and advantages of the present invention will become
apparent from the following descriptions, taken in connection with
the accompanying drawings, wherein, by way of illustration and
example, an embodiment of the present invention is disclosed.
In a preferred embodiment of the present invention, a method for
organizing and compressing spatial data comprises the steps of
parsing a spatial database, separating topographic from attribute
information, segmenting the data into rectangles, eliminating
subsets of the data points, further reducing the data size by
converting the data from a real number format to an integer format,
generating location-relevant file names for each of the rectangles
and storing the files in permanent storage space. In accordance
with a preferred embodiment of the present invention, map display
client software computes data file names based on user interactions
or device-supplied location information (GPS), fetches the computed
file names from a remote server, combines data from several data
files to produce an in-memory map image and draws the image on the
display screen.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings constitute a part of this specification and include
exemplary embodiments to the invention, which may be embodied in
various forms. It is to be understood that in some instances
various aspects of the invention may be shown exaggerated or
enlarged to facilitate an understanding of the invention
wherein:
FIG. 1 is a schematic block diagram illustrating the steps to
generate a compressed spatial database;
FIG. 2 is a sample view of a road segment before and after applying
a data size reduction algorithm;
FIG. 3 is a schematic block diagram illustrating the algorithms
used for data conversion as well as data segment naming;
FIG. 4 is a schematic block diagram showing the different
components and interactions of a network-based map display
system;
FIG. 5 illustrates which file names are computed by the map display
program given a geodetic coordinate;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Detailed descriptions of the preferred embodiment are provided
herein. It is to be understood, however, that the present invention
may be embodied in vanous forms. Therefore, specific details
disclosed herein are not to be interpreted as limiting, but rather
as a basis for the claims and as a representative basis for
teaching one skilled in the art to employ the present invention in
virtually any appropriately detailed system, structure or
manner.
FIG. 1 shows the steps involved in organizing and compressing a
spatial database 10. A spatial database comprises topographic
information in the form of polygons, lines and points expressed in
a geodetic coordinate system (longitude and latitude), and a set of
attributes related to the topographic data entities. It is well
known in the art that functions using spatial data such as routing
or map display only require a subset of the entire data set. For
instance, routing does not need to know about lakes and rivers, and
map display does not need to know about road turn restrictions and
speed limits. It is therefore possible to optimize data sets for
use with a particular function. The purpose of this invention is to
optimize the data set for map display functionality. The
optimization process comprises a number of steps, which are
described in more detail below. The initial step 11 consists of
parsing the geographic database and extracting all the data for a
pre-determined set of features and geographic area. The set of
features comprises roads, railways, airports, rivers, lakes, shore
lines, parks, points of interest and possibly others, depending how
feature-rich the final map display is intended to be. In the
preferred embodiment, the pre-determined geographic area is a
rectangle of 1.degree. longitude and 0.5.degree. latitude, which
will be referred to as a level 2 segment.
The parsed data from step 11 is segmented into topographic
components and attribute components in step 12. Attribute
information is highly redundant and is therefore an obvious
compression target. Attribute information is consolidated using a
simple attribute pointer or index mechanism. The topographic and
attribute components are then further segmented based on location
in two steps. In the preferred embodiment, the first segmentation
evenly divides the area into an 8.times.8 grid. Each topographic
data entity along with its attributes of each selected feature is
assigned to one of the 64 segments. If the data entity is a polygon
or a line and falls into several segments, the data entity is
decomposed into two or more pieces using mathematical line and
polygon splitting algorithms, and each piece is assigned to the
correct segment. The resulting data segments are referred to as
level 1 segments and are stored in non-volatile memory. Another
segmentation is performed on the parsed data from step 11, this
time dividing the area into a 64.times.64 grid. The resulting 4096
data segments are referred to as level 0 data segments, which are
also stored in non-volatile memory.
In step 13, reduction algorithms are performed on level 1 and level
2 data. In the preferred embodiment, level 1 data covers a
geographic area of 1/8.degree. longitude by 1/16.degree. latitude.
When a map picture is generated for such an area, it is neither
desirable nor practical to show all the details, especially when
the map picture is shown on a small screen. For instance, it is
desirable to show only the main roads, while suppressing the
smaller roads. The reduction algorithm used in the preferred
embodiments takes these facts into consideration. Two types of data
reductions are performed. First, some topographic features such as
secondary roads are completely eliminated. Second, the resolution
of the remaining topographic features is reduced. Many road data
entities contain a number of data points, as shown in FIG. 2, which
can be safely eliminated without affecting much the overall
geometry of the line or polygon. For instance, the algorithm used
in the preferred embodiment eliminates every other data point,
provided that the angle between the two lines connecting the point
to its adjacent points does not exceed `n` degrees. Block 20 in
FIG. 2 shows a road segment consisting of data points 21 through
26. Block 27 in FIG. 2 shows the same road after two data points,
22 and 25, have been eliminated using the above algorithm. It
should be obvious from this example that eliminating these data
points did not significantly change the overall shape of the road.
Furthermore, it should be noted that the map resolution at this
level is fairly low, meaning that data points appearing on a
display screen are very close together or even overlapping.
Therefore, eliminating data points as described will have no effect
on what the viewer sees. After processing all 64 level 1 data files
in this way, the level 2 data fill is processed in similar fashion.
Even more topographic features are completely eliminated. For
instance, all roads except for freeways and highways are
eliminated, as well as parks, points of interest and possibly other
features. Resolution of the remaining topographic features is
reduced even further than for level I data, for instance by
applying the algorithm several times to the data set.
Integer conversion as referred to in block 15 of FIG. 1 has two
advantages. It reduces the data size by at least a factor of two,
and it improves processing speed on potentially slow devices. Every
geodetic coordinate is broken into two components: an offset and a
value. The offset may be an aggregation of multiple offsets, but it
always represents the topleft comer of a given rectangle. For any
level 2 data segment (Lx-min, Lx-max, Ly-min, Ly-max), where Lx-min
stands for minimum longitude, Lx-max for maximum longitude, Ly-min
for minimum latitude and Ly-max for maximum latitude, the following
formulas are used to compute offsets and values for each data point
(x, y), where x is the longitude and y the latitude:
X2-offset=Lx-min Y2-offset=Ly-min X2-value=N*(x-x2-offset)
Y2-value=N*(y2-offset-y) N=upper limit of valid integer values
(50000 in the preferred embodiment)
The formulas for computing level 1 offsets and values are:
X1-offset=Abs((x-x2-offset)/((Lx-max-Lx-min)/K))
Y1-offset=Abs((y2-offset-y)/((Ly-max-Ly-min)/K))
X1-value=K*N*(x1-x2-offset-x1-offset)
Y1-value=K*N*(y2-offset-y1-offset-y1) K=segment divisor (8 in the
preferred embodiment for level 1 segments)
The formulas for computing level 0 offsets and values are the same
as for level 1, except that K equals 64 in the preferred
embodiment.
The example shown in FIG. 3 applies the above formulas to convert
the geodetic coordinates 37.308805 and -122.843710 in block 30 in
level 1 integers 1278 and 12516 respectively in block 35.
Level 2 offsets are shown in 31 and 32, while level 1 offsets are
shown in 33 and 34. In the preferred embodiment of this invention,
the upper limit N is set to 50000, but it could be a different
number. The number should not exceed 65536 or 2^16, allowing it to
be stored as a 2 byte integer (a short). The number should not be
too low, which would result in a loss of spatial accuracy, because
several real numbers would map to the same integer. The loss of
accuracy is about 1 meter as implemented in the preferred
embodiment of this invention.
Once a data segment has been processed and all real numbers
converted to integers, a file name is assigned to the data segment
as the last step in block 15 of FIG. 1. Since the computed integer
values are only distance values from a given base value or offset,
they are not reversible to the original real number value without
the offset. A simple and efficient way to supply the necessary
offset values is to make them part of a file name. As shown in the
example of FIG. 3 block 36, a level 1 segment file name is
comprised of a total of 4 numbers representing the 4 offsets used
to compute integer values for that segment, as well as a letter to
indicate the level, the letter `b` representing level 1. The first
number in 36 represents the level 2 latitude offset and the second
number in 36 represents the level 2 longitude offset. The third
number in 36 represents the level 1 latitude offset, and the fourth
number in 36 represents the level 1 longitude offset.
In order to simplify computing requirements, a new geodetic
coordinate system is introduced. The North Pole of the earth is at
coordinate (0,0) and the South Pole is at (360,360). Unlike in the
standard coordinate system, no negative values are used. Every
latitude degree in the standard coordinate system corresponds to 2
latitude degrees in the new system. The conversion from the
standard to the new coordinate system is accomplished as follows:
New latitude=90-old latitude*2
New longitude=old longitude when range is 0.degree. to 180.degree.
New longitude=180+(180-old longitude) when range is-180.degree. to
0.degree.
In the new coordinate system, moving south and east always results
in greater coordinates, while moving west and north always results
in smaller coordinates, until the respective end points 0 and 360
are reached. This system significantly reduces the number of
exception checking operations required by map display software when
compared to the standard coordinate system.
This shows that the file name contains the offset information for
the spatial data stored in the file. Thus, map display software can
perform a few simple calculations to compute a file name from any
geodetic coordinate, which may be supplied by GPS output. It should
also be evident that the task of computing file names for data
segments adjacent to a given segment is very straightforward using
said file-naming system.
The following section describes how a map display program can use
said file system and offer desirable functionality such as combined
online/offline operation. In a typical embodiment, the map display
program is installed on a wireless device such as a smartphone or
personal digital assistant. As shown in FIG. 4, a map display
system 40 consists of several functional components. The input
interface layer 44 handles communication with the user or device. A
text-input component lets the user type location information such
as an address, a city, a zip code or a start/end point of a trip.
The input interface 44 transmits said location information over the
network to a geocoding engine 48 residing on a server 47. As is
well known in the art, a geocoding engine computes a geodetic
coordinate (longitude/latitude) from said information. Once the
input interface 44 receives said geodetic coordinate from the
geocoding engine 48, it notifies the map display engine 46. Some
devices may have voice recognition capabilities. Instead of typing
the user speaks said location information. The input interface 44
transmits the information from the voice recognition system 42 to
the geocoding engine 48, waits for an answer and forwards it to the
map display engine 46. Some devices may have a GPS receiver
attached to or incorporated into the device. The input interface 44
processes the GPS output and relays said output to the map display
engine 46 without the need to communicate with the geocoding engine
48.
The map display engine 46 uses said geodetic coordinates received
from the input interface 44 to calculate four file names. The input
interface 44 also tells the map display engine 46 which data level
is needed, e.g. high-resolution level 0 is appropriate when the
user specified an address, while level 1 may be more appropriate
when the user specified a city or zip code. As has been shown in
detail in a previous section, a geodetic coordinate can be
decomposed and produce a unique file name. The map display engine
46 could then request said file name from a server 47 on which all
files 49 are stored. However, in the preferred embodiment, the map
display engine actually computes a total of four file names. If
only one file is fetched, the geodetic coordinate of interest to
the user could be located somewhere near the edge of said file. It
would look awkward to the user and be less informative if the point
of interest is not shown at or near the center of the map display
screen. The ability to center the map picture has been lost by
segmenting the spatial database. The solution employed by the map
display engine 46 is to fetch three additional data segment files,
which are most adjacent to said geodetic coordinate. The map
display engine simply determines into which area, top-left,
top-right, bottom-left or bottom-right, said coordinate falls. If a
point falls in the top-left quadrant of a file, as does point 54 in
FIG. 5, the map display program first finds file 105.237.3.1.b
shown in block 53, and then also fetches the file to the top, block
51, to the left, block 52, and to the top-left, block 50. After
fetching all 4 files from the server 47, the map display engine
combines the data of the 4 files using simple offset calculations
before drawing the map picture to the screen. Said geodetic
coordinates can now be displayed fairly close (within 25%) of the
screen center. An even better center approximation could be
achieved by using nine files. Perfect centering can be achieved by
not showing a map picture of the entire available data, but instead
generate a slightly zoomed-in map picture centered at said
coordinate.
One objective of the invention is to provide a flexible mapping
system in the sense that the map display system can function online
as well as offline. Offline functionality is desirable because it
offers the highest speed, since the data is accessed from local
storage. The map display engine 46 gives users several options to
enable offline capability. Users can select a city or zip code and
download all data files for said city or zip code. Furthermore,
users can reserve a certain amount of local disk space to be
allocated for map data caching. When caching is enabled, the map
display engine 46 automatically stores downloaded files on the
local disk. As the cache fills up, new data files replace the least
frequently accessed data files. A different caching algorithm, for
instance based on last accessed time stamps, could be used as well.
When the user has selected caching or pre-loading of data, the map
display engine 46 always first scans the local disk space and, if
available, loads data files from local space into memory instead of
downloading said files from a remote server. Local caching is very
useful when users frequently request the same maps. For instance, a
user may want to check road traffic conditions on a daily basis. In
this case, only updated traffic information such as traffic
incident locations or traffic speed maps (a list of measured
traffic speeds at different locations) needs to be downloaded. Said
updated traffic information can be displayed on a map, which is
generated from the map display engine 46 using local map data. Said
offline/online capability offers optimal performance for frequently
used maps as well as great flexibility regarding local storage
capacities of different devices.
While the invention has been described in connection with a
preferred embodiment, it is not intended to limit the scope of the
invention to the particular form set forth, but on the contrary, it
is intended to cover such alternatives, modifications, and
equivalents as may be included within the spirit and scope of the
invention as defined by the appended claims.
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