U.S. patent application number 12/451634 was filed with the patent office on 2010-06-03 for positioning device and method to determine a position using an absolute positioning system and a relative positioning system, computer program and a data carrier.
Invention is credited to Stephen T'Siobbel.
Application Number | 20100138147 12/451634 |
Document ID | / |
Family ID | 38984455 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100138147 |
Kind Code |
A1 |
T'Siobbel; Stephen |
June 3, 2010 |
POSITIONING DEVICE AND METHOD TO DETERMINE A POSITION USING AN
ABSOLUTE POSITIONING SYSTEM AND A RELATIVE POSITIONING SYSTEM,
COMPUTER PROGRAM AND A DATA CARRIER
Abstract
A positioning device is arranged to determine a position using
an absolute positioning system and a relative positioning system.
The positioning device is arranged, in at least one embodiment, to
work in a first mode, in which the position is determined using the
absolute positioning system and possibly the relative positioning
system, and in a second mode, in which the position is determined
using the relative positioning system and possibly the absolute
positioning system. In the first mode the absolute positioning
system is weighted more heavily than in the second mode and the
positioning device is arranged to switch from the first to the
second mode. The positioning device has access to a digital map
database in at least one embodiment and the switch from the first
to the second mode is decided based on at least the determined
position in combination with information stored in the digital map
database.
Inventors: |
T'Siobbel; Stephen;
(Merelbeke, BE) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
38984455 |
Appl. No.: |
12/451634 |
Filed: |
May 24, 2007 |
PCT Filed: |
May 24, 2007 |
PCT NO: |
PCT/NL2007/050246 |
371 Date: |
January 19, 2010 |
Current U.S.
Class: |
701/533 |
Current CPC
Class: |
G01C 21/165 20130101;
G01S 19/49 20130101; G01S 19/22 20130101; G01S 5/0263 20130101;
G01C 21/30 20130101 |
Class at
Publication: |
701/201 ;
701/208 |
International
Class: |
G01C 21/00 20060101
G01C021/00; G01S 5/14 20060101 G01S005/14 |
Claims
1. Positioning device arranged to determine a position using an
absolute positioning system and a relative positioning system, the
positioning device being arranged to work in a first mode, in which
the position is determined using at least one of the absolute
positioning system and the relative positioning system, and in a
second mode, in which the position is determined using at least one
of the relative positioning system and the absolute positioning
system, in the first mode the absolute positioning system being
weighted relatively more heavily than in the second mode to
determine the position, and the positioning device being arranged
to switch from the first mode to the second mode, the positioning
device at least one of comprising and having access to a digital
map database, and the switching from the first to the second mode
being decided based on at least the determined position in
combination with information stored in the digital map
database.
2. Positioning device according to claim 1, wherein the absolute
positioning system is one of a satellite based positioning system
and a terrestrial positioning system.
3. Positioning device according to any claim 1, wherein the
relative positioning system is at least one of a gyroscope, an
accelerometer, a compass, a velocity measurement module, a distance
meter, an inclinometer and a module detecting steering actions of a
steering wheel.
4. Positioning device according to claim 1, wherein the information
stored in the digital map database comprises a plurality of
geographical objects having threshold distances associated with
them.
5. Positioning device according to claim 4, wherein the positioning
device is arranged to compute at least one distance from the
determined position to a selection of the plurality of geographical
object, wherein threshold distances are associated with the
plurality of geographical objects, and wherein the switch from the
first to the second mode is made if at least one of the at least
one computed distance is below a respective associated
threshold.
6. Positioning device according to claim 2, wherein the absolute
positioning system is arranged to determine a position based on
signals received from a plurality of transmitters which are part of
the satellite based positioning system or the terrestrial
positioning system.
7. Positioning device according to claim 6, wherein the digital map
database is a three dimensional digital map database, wherein the
information comprises three dimensional information about
geographical objects, and wherein the positioning device is
arranged to compute a quality of a position as determined by the
absolute positioning system based on at least one of the determined
position, the position of the transmitters and the three
dimensional digital map database.
8. Positioning device according to claims 6, wherein the
positioning device is arranged to determine the respective
positions of the transmitters based on position information
comprised by the respective signals.
9. Positioning device according to claim 1, wherein a further
switch from the second to the first mode is decided based on a
determined position in combination with information stored in the
digital map database.
10. Positioning device according to claim 1, wherein the
positioning device is arranged to maintain a history file
comprising previously determined positions and associated
accuracies as determined according to the absolute positioning
system and, when a switch is made from the first mode to the second
mode, the positioning device is arranged to select a starting
position for the relative positioning system from the history
file.
11. Positioning device according to claim 1, wherein the
positioning device is arranged to determine accuracies of
determined positions in one mode, compare the determined accuracy
of positions with a threshold value and in case the accuracy is
below the threshold value, and store these positions as a
geographical object with an advised mode associated with it, the
advised mode being different from the one mode.
12. Method for determining a position, comprising: determining a
position using an absolute positioning system and a relative
positioning system, the position being determinable in a first
mode, in which the position is determined using at least one of the
absolute positioning system and the relative positioning system,
and in a second mode, in which the position is determined using at
least one of the relative positioning system and the absolute
positioning system, in the first mode the absolute positioning
system being weighted relatively more heavily to determine the
position than in the second mode; deciding whether or not to switch
from the first mode to the second mode based the determined
position in combination with information stored in a digital map
database; and switching from the first mode to the second mode if
it is decided to switch.
13. Method according to claim 12, wherein the absolute positioning
system is one of a satellite based positioning system and
terrestrial positioning system.
14. Method according to claim 12, wherein the relative positioning
system is at least one of a gyroscope, an accelerometer, a compass,
a velocity measurement module, a distance meter, a module detecting
steering actions of a steering wheel, and an inclinometer.
15. Method according to claim 12, wherein the information stored in
the digital map database comprises a plurality of geographical
objects including associated threshold distances.
16. Method according to claim 15, further comprising: computing at
least one distance from the determined position to a selection of
the plurality of geographical objects having associated threshold
distances, the switching from the first to the second mode being
done if at least one of the computed distances is below a
respective associated threshold.
17. Method according to claim 12, wherein the absolute positioning
system APS) is arranged to determine a position based on signals
received from a plurality of transmitters being part of the
satellite based positioning system or the terrestrial positioning
system.
18. Method according to claim 17, wherein the digital map database
is a three dimensional digital map database, and the information
comprises three dimensional information about geographical objects,
the method further comprising: computing a quality of a position as
determined by the absolute positioning system based on at least one
of the determined position, the position of the transmitters and
the three dimensional digital map database.
19. Method according to claim 17, further comprising: determining
the respective positions of the transmitters based on position
information comprised by the respective signals.
20. Method according to claim 12, further comprising: keeping a
history file comprising previously determined positions and
associated accuracies as determined according to the absolute
positioning system and the relative positioning system, and
selecting, upon the switch is made from the first mode to the
second mode, a starting position for the relative positioning
system from the history file.
21. Method according to claim 12, further comprising determining
accuracies of determined positions in one of the first and second
mode; comparing the determined accuracy of positions with a
threshold value; and storing, in case the comparison indicates that
the accuracy is below the threshold value, the positions as a
geographical object with an associated advised mode, the advised
mode being different from the one of the first and second
modes.
22. Computer program, which when loaded on a computer arrangement,
is arranged to perform the according to claims 12.
23. Data carrier, comprising the computer program according to
claim 22.
24. Positioning device according to claim 2, wherein the relative
positioning system is at least one of a gyroscope, an
accelerometer, a compass, a velocity measurement module, a distance
meter, an inclinometer and a module detecting steering actions of a
steering wheel.
25. Method according to claim 18, further comprising: determining
the respective positions of the transmitters based on position
information comprised by the respective signals.
26. Computer readable medium comprising program segments which,
when executed on a computer device, perform the method of claim 12.
Description
TECHNICAL FIELD
[0001] The present invention relates to a positioning device and
method to determine a position using an absolute positioning system
and a relative positioning system, a computer program and a data
carrier.
BACKGROUND
[0002] Global Navigation Satellite Systems (GNSS), such as the
global positioning system (GPS-system) are used worldwide by users
to determine their position (longitude, latitude, altitude) on
earth.
[0003] The GPS-system comprises a number of satellites orbiting the
earth, each satellite transmitting radio signals comprising precise
timing information about the time the radio signals are transmitted
by the satellite. The radio signals also comprise position
information (orbital information) comprising information about the
position of the respective satellite, and a satellite
identification that is unique for a specific satellite.
[0004] Positioning devices, such as GPS-receivers, are arranged to
receive these signals and compute their position based on the
received signals. Such positioning devices provide absolute
positioning information with respect to an absolute frame of
reference and may therefore also be referred to as absolute
positioning systems.
[0005] Positioning devices are arranged to receive these
transmitted radio signals and compute the travel time of such a
radio signal based on the timing information comprised by the radio
signal and a measured time of arrival of the radio signal using a
clock comprised by the positioning device. The travel time is
usually 65-85 milliseconds. Based on the travel time, the distance
of the positioning device to the satellite can be computed, simply
by multiplying the travel time with the speed of light
(c=299.792.458 m/s). Based on the received orbital information
comprised by the radio signal, the positioning device can compute
the position of the satellite. By combining the information of the
distance to the satellite and the position of the satellite, the
positioning device is placed on an imaginary sphere whose radius
equals the distance and whose centre is the satellite.
[0006] By repeating this computation process for at least four
satellites, the positioning device can compute four of such
imaginary spheres, defining one intersection, which defines the
position of the positioning device.
[0007] Positioning devices are often used in navigation devices
comprising digital map data. Such navigation devices may be
arranged to show the position as determined on the digital map
using a display. Such a navigation device may be referred to as a
map displaying device, where the part of the displayed map is
determined by the actual position as determined by the positioning
device.
[0008] Also, such navigation devices may be arranged to compute
navigation instructions from a start position (for instance the
current position) to a destination position, to guide the user to
the destination address. Since the positioning device is able to
position the current position on the digital map, the navigation
device is capable of providing detailed navigation instructions,
such as: "after 100 metres, turn left". It will be understood that
accurate positional information is needed for such applications in
order to ensure optimal navigation and optimal user comfort.
[0009] In order to increase the accuracy of the position as
determined by the positioning device using the absolute positioning
system, the positioning device may use more than four satellites.
Generally, a positioning device uses information from all
satellites from which it receives radio signals. In general, the
more satellites are used, the more accurate the determined
position.
[0010] The accuracy of the position as determined by the
positioning device is influenced by a number of factors, such as
the computed position of the satellite, the computed travel time of
the radio signal, the current time as determined by the clock of
the positioning device. A number of techniques are known to
decrease the effect of these system errors, such as WAAS (Wide Area
Augmentation System) and DGPS (differential GPS), as will be known
to a skilled person.
[0011] The accuracy of the determined position may be further
increased by using a technique called map matching. This technique
introduced a further increase in the accuracy of the determined
position, by mapping the position as determined to a street or the
like as stored in the map database.
[0012] However, also a number of further outside errors can be
identified reducing the accuracy of the determined position, such
as ionospheric effects, errors of the satellite clocks etc. One
special type of error is so-called multi-path distortion.
[0013] Multi-path occurs in situations in which the radio signal as
transmitted by a satellite is reflected by an object, such as a
building, and the positioning device receives the radio signal
after reflection, possibly together with a not-reflected radio
signal. As a result, the computed distance between the satellite
and the positioning device introduces an error in the computed
position of the positioning device.
[0014] Positioning devices may also comprise or interact with a
relative positioning system to generally improve the positioning
accuracy of the absolute positioning system or to determine a
position in situations in which no or not enough radio signals can
be received. Relative positioning systems provide local and
relative positioning information.
[0015] These relative positioning systems may for instance be at
least one of a gyroscope, an accelerometer, a compass, a distance
meter (such as an odometer), an inclinometer. In case the
positioning device is used in a vehicle, such as a car or motor
cycle, the relative positioning device may also be a
distance/velocity measurement module as usually present in such a
vehicle and/or a module detecting steering actions of a steering
wheel and/or other sensors that may be present in the vehicle.
[0016] Situations in which more emphasis may be put on the relative
positioning systems (i.e. information from the relative position
system is weighted more heavily) , are for instance when the
positioning device enters a tunnel or an underground parking The
positioning device will no longer be able to determine its position
using the absolute positioning system, as not enough radio signals
are received. Inside the tunnel or underground parking, the
positioning device uses information received from or obtained with
the relative positioning system.
[0017] For instance, a gyroscope provides information about
relative rotational movement. In combination with the last obtained
position based on the absolute positioning system and the distance
meter, this may be used to compute a current position within the
tunnel or underground parking.
[0018] U.S. Pat. No. 5,311,195 describes a navigation system using
a combination of an absolute positioning system, such as a
GPS-receiver and a relative positioning system, such as an onboard
wheel sensor and/or an magnetic compass. According to U.S. Pat. No.
5,311,195 the position as determined by the relative positioning
system is updated by the position as determined by the absolute
positioning system in case a contour of equal probability of a
position determined by the relative positioning system overlaps a
contour of equal probability of a position determined by the
absolute positioning system. So, in case the accuracy of the
relative positioning system is low, the absolute positioning system
may be used to update the relative positioning system.
[0019] According to the prior art, positioning devices are arranged
to determine a position using an absolute positioning system and a
relative positioning system, and are further arranged to work
[0020] in a first mode, in which the position is determined using
the absolute positioning system and possibly the relative
positioning system, and
[0021] in a second mode, in which the position is determined using
the relative positioning system and possibly the absolute
positioning system,
[0022] where in the first mode the absolute positioning system is
weighted more heavily to determine the position than in the second
mode. The positioning devices are arranged to switch from the first
mode to the second mode and vice versa, based on determined
accuracies of the absolute and/or relative positioning systems.
[0023] Based on the above, it is an object to provide a positioning
device and method that provides more accurate positional
information.
SUMMARY
[0024] According to an aspect there is provided a positioning
device arranged to determine a position using an absolute
positioning system and a relative positioning system, and further
arranged to work
[0025] in a first mode, in which the position is determined using
the absolute positioning system and possibly the relative
positioning system, and
[0026] in a second mode, in which the position is determined using
the relative positioning system and possibly the absolute
positioning system,
[0027] in the first mode the absolute positioning system being
weighted more heavily than in the second mode to determine the
position and the positioning device is arranged to switch from the
first mode to the second mode, characterized in that the
positioning device comprises or has access to a digital map
database, and the switch from the first to the second mode is
decided based on at least the determined position in combination
with information stored in the digital map database. Such a
positioning device provides a more accurate determination of the
position, as the switch from one mode to another mode may be made
before the quality of the one mode has deteriorated too much.
[0028] According to an embodiment the absolute positioning system
is one of a satellite based positioning system and a terrestrial
positioning system.
[0029] According to an embodiment the relative positioning system
is at least one of a gyroscope, an accelerometer, a compass, a
velocity measurement module, a distance meter, an inclinometer and
a module detecting steering actions of a steering wheel.
[0030] According to an embodiment, the information stored in the
digital map database comprises a plurality of geographical objects
having threshold distances associated with them.
[0031] According to an embodiment the positioning device is
arranged to compute at least one distance from the determined
position to a selection of the plurality of geographical objects
having threshold distances associated with them and the switch from
the first to the second mode is made if at least one of the
computed distances is below the respective associated
threshold.
[0032] According to an embodiment the absolute positioning system
is arranged to determine a position based on signals received from
a plurality of transmitters being part of the satellite based
positioning system or the terrestrial positioning system.
[0033] According to an embodiment the digital map database is a
three dimensional digital map database, and the information
comprises three dimensional information about geographical objects,
wherein the positioning device is arranged to compute a quality of
a position as determined by the absolute positioning system based
on at least one of the determined position, the position of the
transmitters and the three dimensional digital map database.
[0034] According to an embodiment the positioning device is
arranged to determine the respective positions of the transmitters
based on position information comprised by the respective
signals.
[0035] According to an embodiment a further switch from the second
to the first mode is decided based on a determined position in
combination with information stored in the digital map
database.
[0036] According to an embodiment the positioning device is
arranged to keep a history file comprising previously determined
positions and associated accuracies as determined according to the
absolute positioning system and, when a switch is made from the
first mode to the second mode, the positioning device is arranged
to select a starting position for the relative positioning system
from the history file.
[0037] According to an embodiment the positioning device is
arranged to determine accuracies of determined positions in one
mode, compare the determined accuracy of positions with a threshold
value and in case the accuracy is below the threshold value, store
these positions as a geographical object with an advised mode
associated with it, the advised mode being different from the one
mode.
[0038] According to an aspect there is provided a method, the
method comprises determining a position using an absolute
positioning system and a relative positioning system, the position
can be determined
[0039] in a first mode, in which the position is determined using
the absolute positioning system and possibly the relative
positioning system, and
[0040] in a second mode, in which the position is determined using
the relative positioning system and possibly the absolute
positioning system,
[0041] in the first mode the absolute positioning system being
weighted more heavily to determine the position than in the second
mode and the method further comprising switching from the first
mode to the second mode,
[0042] characterized in that the method comprises an action to
decide whether or not to switch from the first mode to the second
mode based the determined position in combination with information
stored in a digital map database.
[0043] According to an aspect, there is provided a computer
program, that when loaded on a computer arrangement, is arranged to
perform any one of the methods according to the above.
[0044] According to an aspect, there is provided a data carrier,
comprising a computer program according to the above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The present invention will now be discussed in more detail
using a number of exemplary embodiments, with reference to the
drawings, which are only intended to illustrate the present
invention and not to limit its scope which is only limited by the
appended claims:
[0046] FIG. 1 schematically depicts a positioning device according
to the prior art,
[0047] FIG. 2 schematically depicts a positioning device
interacting with satellites, and
[0048] FIGS. 3, 4 and 5 schematically depict flow diagrams
according to embodiments.
DETAILED DESCRIPTION
[0049] As already briefly described above, the positioning device
may be arranged to work in a first mode, in which positions are
determined using an absolute positioning system, and a second mode,
in which positions are determined using a relative positioning
system. Such a positioning device may comprise a processing unit PU
comprising or interacting with such an absolute and relative
positioning system. The processing unit PU may also be arranged to
switch from the first to the second mode and vice versa. First the
processing unit PU of such a positioning device is described in
more detail.
[0050] Processing Unit
[0051] The processing unit PU is shown schematically in FIG. 1, but
it will be understood that the processing unit PU may be formed as
a computer unit, for instance comprising a processor for performing
arithmetical operations and memory, the memory comprising
programming lines readable and executable by the processor to
provide the positioning device PD with the functionality described
here.
[0052] The memory may be a tape unit, hard disk, a Read Only Memory
(ROM), Electrically Erasable Programmable Read Only Memory (EEPROM)
and a Random Access Memory (RAM).
[0053] The processing unit PU may further comprise or be arranged
to communicate with
[0054] input devices, such as a keyboard, a mouse, a touch screen,
a speaker,
[0055] output devices, such as a display, a printer,
[0056] reading devices to read data carriers, such as for instance
floppy disks, CD ROM's, DVD's FLASH cards, USB-sticks and the like
and
[0057] communication devices arranged to communicate with other
computer systems via a communication network, such as via a mobile
telephone network, a GSM-network, a UMTS-network, a RF-network,
(wireless) Internet etc.
[0058] The processing unit PU may be arranged to receive
information from a relative positioning system (also referred to as
autonomous positioning system) as explained in more detail below
using suitable input devices or reading devices.
[0059] However, it should be understood that there may be provided
more and/or other memories, input devices, output devices and read
devices known to persons skilled in the art. Moreover, one or more
of them may be physically located remote from the processor unit
PU, if required. The processor unit PU is shown as one box,
however, it may comprise several processor units functioning in
parallel or controlled by one main processor unit that may be
located remote from one another, as is known to persons skilled in
the art.
[0060] The processing unit PU may further comprise or be arranged
to communicate with a clock CL and an antenna AN. The clock CL may
be used in combination with the absolute positioning system. The
antenna AN may be used to receive signals from e.g. satellites of
the absolute positioning system.
[0061] It is observed that, the connections between different
hardware elements may be physical connections, but one or more of
these connections can be made wireless.
[0062] The processing unit PU may be a computer system, but can be
any signal processing system with analog and/or digital and/or
software technology arranged to perform the functions discussed
here.
[0063] Absolute Positioning System
[0064] FIG. 2 shows a positioning device PD as already described
above using an absolute positioning system to determine its
position. The positioning device PD comprises a processor unit PU,
an antenna AN and a clock CL. The antenna AN is arranged to receive
radio signals transmitted by satellites SA1, SA2 and transmit these
received radio signals to the processor unit PU. Although the
antenna AN is depicted as a part extending from the positioning
device PD, it will be understood that the antenna AN may also be a
formed inside the positioning device PD. The clock CL is arranged
to provide accurate time information to the processor unit PU.
[0065] As already described above, the processor unit PU may be
arranged to receive radio signals from satellites SA1, SA2 via
antenna AN. From these radio signals, the processor unit PU gathers
information, such as timing information about the time the radio
signals were transmitted by the satellite, orbital information
comprising information about the position of the respective
satellite and a satellite identification of the satellite SA1,
SA2.
[0066] The processor unit PU may further be arranged to determine
time of arrival of radio signals, using the time information
received from the clock CL. Based on the time information about the
time the radio signals were transmitted by the satellite and the
time information from clock CL, the processor unit PU can compute
the travel time of the radio signal (subtracting one from the
other), and the distance between the positioning device PD and the
respective satellite (by multiplying the travel time with the speed
of light).
[0067] By combining information from a number of satellites (at
least four) the position of the positioning device PD can be
computed.
[0068] FIG. 2 further shows that the positioning device PD is
positioned near an entrance of a tunnel or underground parking In
fact, the positioning device PD may be near any kind of object that
may block radio signals transmitted by a satellite, such as a
building, tree, hill, mountain, viaducts etc. FIG. 2 further
schematically shows a first satellite SA1, a second satellite SA2
and a third satellite SA3 orbiting the earth. It will be understood
that although only three satellites SA1, SA2, SA3 are shown in FIG.
2 in fact, more than three satellites SA1, SA2, SA3 will usually be
present.
[0069] The first satellite SA1 transmits radio signals, indicated
with the dotted line. It can be seen that the radio signals can be
detected by the positioning device PD. The processor unit PU can
now compute the distance from the positioning device PD to the
first satellite SA1.
[0070] The second satellite SA2 also transmits radio signals, also
indicated with the dotted line. However, these radio signals suffer
multi-path distortion, as the radio signal from the second
satellite SA2 travels to the antenna AN of the positioning device
PD directly (see radio signal a in FIG. 2) as well as indirectly
(see radio signal b), i.e. via a reflection of the entrance of the
tunnel TU.
[0071] If the processor unit PU now computes the distance between
the positioning device PD and the second satellite SA2 by computing
the travel time, it will be understood that an erroneous distance
will result, because of the multi-path distortion. This erroneous
distance will lead to an erroneous determined position of the
positioning device PD, even when used in combination with
information obtained from a plurality of satellites SA1, SA2.
[0072] Radio signals from the third satellite SA3 can not be
received by the positioning device at all, as they are completely
blocked by the tunnel TU.
[0073] It will be understood that the examples of the absolute
positioning system described here, are not restricted to
GPS-systems. The embodiments described may be used in combination
with any kind of absolute positioning system using signals being
sent wirelessly from a plurality of transmitters to a receiver,
such as a positioning device PD, enabling the receiver to compute
its position based on the received signals.
[0074] It is to be understood that such signals usually have a low
power intensity which make them relatively difficult to detect for
positioning devices.
[0075] The absolute positioning system may be any kind of satellite
based positioning system or global navigation satellite system
(GNSS), such as the GPS-system, GLONASS and Galileo.
[0076] The absolute positioning system may also be a terrestrial
positioning system, using beacons positioned on land or sea that
transmit signals comprising information that may be used by a
receiver to determine its position. An example of such a
terrestrial system is LORAN (LOng RAnge Navigation). Another
example of such a system may be a terrestrial system using mobile
telephone masts (such as GSM masts) as beacons.
[0077] In general the absolute positioning system comprises a
plurality of transmitters, such as satellites or beacons, arranged
to wirelessly transmit signals, such as radio signals, that may be
received by a receiver, such as a positioning device PD that is
arranged to compute its position based on the received signals.
[0078] Relative Positioning System
[0079] According to the embodiments described here, the positioning
device PD may comprise or interact with a relative positioning
system RPS, as schematically depicted in FIG. 1. As described
above, such a relative positioning system RPS may for instance be
at least one of a gyroscope, an accelerometer, a compass, a
distance meter (such as an odometer), an inclinometer. In case the
positioning device PD is used in a vehicle, such as a car or motor
cycle, the relative positioning system RPS may also be a
distance/velocity measurement module as usually present in such a
vehicle and/or a module detecting steering actions of a steering
wheel and/or other sensors that may be present in the vehicle.
[0080] It will be understood that also other relative positioning
systems RPS may be used. Also, a combination of different relative
positioning systems RPS may be used.
[0081] For instance, the positioning device PD may be arranged to
receive input from a velocity measurement module and a (n
electronic) compass. Based on the input received from these
modules, the processor unit PU of the positioning device PD may
compute a relative position, as it is able to compute how far the
positioning device PD has travelled in which direction.
[0082] According to the prior art, the positioning device PD may be
arranged to work
[0083] in a first mode, in which the position is determined using
the absolute positioning system and possibly the relative
positioning system, and
[0084] in a second mode, in which the position is determined using
the relative positioning system and possibly the absolute
positioning system,
[0085] where in the first mode the absolute positioning system is
weighted more heavily to determine the position than in the second
mode. The switch from the first mode to the second mode may be
triggered by comparing estimates of accuracies of the positions as
determined by both systems. Also, when no absolute position
determination is possible, for instance when the positioning device
PD enters a tunnel or underground parking the positioning device
may shift from first to second mode.
[0086] From the above it will be clear that in the first mode and
the second mode the positional information as obtained from the
absolute and the relative positioning system may be combined by
weighting, filtering, mixing etc. to obtain a determined position
of the positioning device.
[0087] Of course, further modes may be applied, using different
weighting of the absolute positioning system and the relative
positioning system than in the first and second mode. Also, it will
be understood that according to an embodiment, the relative
positioning system is not taken into account at all in the first
mode and/or the absolute positioning system is not taken into
account at all in the second mode.
[0088] In the second mode, the positioning device PD uses relative
positioning information provided by the relative positioning system
RPS. The relative positioning information is used in combination
with a starting position (e.g. the most recent position as
determined by the absolute positioning system or the previous mode)
to determine a current position.
[0089] However, it is identified that switching from the first to
the second mode and/or vice versa, according to the prior art may
result in inaccurate positioning information, as the switch is
usually made on a moment in time on which the position as
determined according to the initial mode is already relatively
inaccurate.
[0090] For instance, an error in the starting position used by the
relative positioning system RPS as determined by the first mode
before switching from the first to the second mode, will effect all
the subsequent positions determined in the second mode, as the
starting position is used as a basis for these. Therefore, an
improvement is provided to ensure that more accurate positioning
information is computed.
[0091] Digital Map Database
[0092] Positioning devices PD may comprise or have access to
digital map databases DMD. The positioning device PD may be
arranged to show a current position on a digital map using a
display. However, the positioning device PD may also be arranged to
provide navigation instructions from a start position (for instance
the current position) to a destination position, to guide the user
to the destination address.
[0093] It will be understood that the term digital map database as
used here does not necessarily refer to a database structure in the
traditional way, i.e. does not imply relational structure between
the database entries or a database manager coordinating the
database. The digital map database as used here refers to any set
of geospatial information, regardless of the exact way the
information is structured.
[0094] The term geographical object as used here may correspond to
a real-life object, such as a tunnel, building, tree, hill etc.,
but also correspond to a certain position in general.
[0095] Digital map databases DMD, also known as geospatial
databases, navigation maps or electronic maps, are known in the
prior art. Digital map databases DMD in common usage today may
comprise geographical objects (also referred to as geographical
points) related to geographic location(s) and possibly incorporate
some form of geographically related information, such as points of
interest (museum, restaurant), (underground) parkings, tunnels,
bridges and the like. In this application, the term digital map
database DMD is used to denote all kinds of electronic and digital
maps.
[0096] Digital map databases DMD may comprise a set of geographical
objects and a set of vectors, representing (parts of) roads,
connecting geospatial objects. The digital map database DMD may
further comprise additional information, for instance relating to
the type of road (highway, foot path), maximum allowable speed (50
km/h, 100 km/h), street names, the presences of objects, such as
tunnels and underground parkings etc. The digital map database DMD
may further also comprise information about type of environment
(urban, rural, forest, agriculture) and the like.
[0097] The digital map database DMD may be used to compute
navigation instructions to guide a user to a destination, as
mentioned above. Depending on the current position of the user as
determined by the positioning device, a part of the digital map
database DMD may be displayed on a display.
[0098] The digital map database may be a 3D digital map databases
3DMD, comprising three dimensional information, for instance about
geographical objects such as buildings, trees, rocks, mountains,
tunnels, (underground) parkings etc. The 3D digital map database
3DMD may further comprise information about urban canyons and/or
city models.
[0099] Such a 3D digital map database 3DMD may comprise information
about the position of objects, including the horizontal and
vertical dimensions of such objects. The 3D digital map database
3DMD may also comprise information about the shape of such
geographical objects, which may for instance be relevant in case of
a building having a gabled roof (peaked roof).
Embodiments
[0100] According to an embodiment, the positioning device PD is
arranged to switch from the first mode to the second mode using
information from the digital map database DMD or 3-dimensional
digital map database 3DMD.
[0101] According to a further embodiment, the positioning device PD
is arranged to switch from the second mode to the first mode based
on information from the digital map database DMD or 3-dimensional
digital map database 3DMD.
[0102] It will be understood that the second mode may also
exclusively use information from the relative positioning system
and no information from the absolute positioning system. This may
for instance be the case in situations where no absolute
positioning is possible, for instance in a tunnel or the like. In
such a case, when the positioning device PD is in the second mode,
the relative positioning information as determined by the relative
positioning system RPS can only be translated into an absolute
position, using the starting position described above, for instance
being a previously determined absolute position, determined in the
first mode or by the absolute positioning system.
[0103] According to the prior art switching from the first mode to
the second mode was triggered based on the identification that the
quality or accuracy of the position as determined was relatively
bad, for instance because less radio signals were received.
However, as a result from switching from the first mode to the
second mode when the determined position lacks accuracy, the
starting position used as a basis for the relative position system,
is of a relative low quality or is relatively inaccurate. This may
for instance be the case because the switch from the first to the
second mode is made on a moment that the positioning device PD
already entered the tunnel TU. Therefore, all the positions
determined using the relative positioning system are relatively
inaccurate because of the relatively inaccurate starting
position.
[0104] According to embodiments provided here, switching from the
first to the second mode is done in a more sophisticated way, i.e.
before the quality of the position as determined in the first mode
has decreased too much. The switch from the first to the second
mode is triggered by using information from the digital map
database DMD or the 3-dimensional digital map database 3DMD.
[0105] Also, according to embodiments provided here, switching from
the second to the first mode is done when the quality of the
position as determined by the first mode is sufficiently high. The
switch from the second to the first mode is triggered by using
information from the digital map database DMD or the 3-dimensional
digital map database 3DMD.
[0106] By using information from the digital map database, the
timing of switching from one mode to another may be timed more
accurately, resulting in more accurate positioning information.
Embodiment 1
[0107] According to an embodiment, the digital map database DMD may
comprise a geographical object, such as the position of e.g. a
tunnel TU, or the position of a tree, building, viaduct and the
like. Together with this geographical object, a threshold distance
may be stored in the digital map database DMD, for instance of 50
metres, indicating that the quality of the positioning in the first
mode is poor within that distance from the tunnel TU and the
positioning device PD should switch from the first mode to the
second mode when being less than for instance 50 metres away from
the tunnel TU.
[0108] Each specific geographical object may have its own threshold
associated with it. Also, standard threshold distances may be
provided for specific type of geographical objects, such as 50
metres for tunnels and 30 metres for trees.
[0109] According to such an embodiment, the positioning device PD
may have access to the digital map database DMD. Based on the
information stored in the digital map database DMD, for each
position of the positioning device PD, the positioning device PD
may compute if it is too close to a geographical object and the
quality of the positions as determined in the first mode will
probably deteriorate too much. When the positioning device PD
determines it is too close to an object, the positioning device PD
switches to the second mode.
[0110] Also, when the positioning device PD is in the second mode,
and the positioning device PD detects that it is no longer within
threshold distance from a geographical distance, it may switch back
from the second mode to the first mode.
[0111] Of course, this embodiment could also work in combination
with a 3-dimensional digital map database 3DMD comprising threshold
distances.
[0112] Flow Diagram 1
[0113] FIG. 3 schematically depicts a flow diagram depicting
actions as may be performed by the positioning device PD or the
processing unit PU according to an embodiment.
[0114] In a first action 100, the positioning device PD may start
executing the flow diagram as described here. The start may be
triggered manually by a user or may for instance be triggered by
switching on the positioning device PD.
[0115] In a second action 101, the positioning device PD determines
its position in the first mode, using input from the absolute
positioning system APS and possibly from the relative positioning
system RPS.
[0116] Once a position is determined, the positioning device PD may
compute its distance to nearby geographical objects having a
threshold associated with it, for instance all such geographical
objects within a range of 100 metres. This is done in an action
102. For performing this action, input from the digital map
database DMD is used.
[0117] In a next action 103, the computed distances to nearby
geographical objects are compared with the appropriate distance
thresholds, associated with the geographical objects.
[0118] If the positioning device PD is not too close to a
geographical object, in action 104 it is decided to return to
action 101 and determine an updated position in the first mode. If
the positioning device PD is too close to a geographical object, in
action 104 it is decided to proceed to action 105 and determine an
updated position in the second mode.
[0119] After action 101 and 105, actions 102, 103 and 104 are
executed. This ensures that the positioning device PD automatically
switches from the first mode to the second mode and vice versa when
necessary and possible.
Embodiment 2
[0120] According to a further embodiment, the processor unit PU may
have access to a 3D digital map database 3DMD. According to such an
embodiment, the positioning device PD may compute, based on the
three dimensional information about geographical objects stored in
the 3D digital map database 3DMD for each position of the processor
unit PU if the quality of the absolute positions as determined by
the absolute positioning system will be such that the processor
unit PU should switch to the second mode, in which the absolute
positioning system APS is weighted less heavily.
[0121] So, where the first embodiment uses predetermined threshold
distances that are stored in the digital map database or the 3D
digital map database, according to this embodiment, switching form
one mode to the other is determined on the spot using information
from the 3D digital map database.
[0122] The processor unit PU may for instance compute when it will
reach or has reached a position where multi-path distortion is
likely to occur. It will be understood that the processor unit PU
has knowledge of the current positions of the satellites SA1, SA2,
SA3 from which signals are received, as this information is
comprised by the signals (orbital information). Using this
information in combination with the shape and size of geographical
objects close to the latest determined position, which is stored in
the 3-dimensional digital map database 3DMD, the processor unit PU
can compute for which satellites multi-path distortion is likely to
occur by applying straightforward geometry.
[0123] According to an alternative, the processor unit PU may for
instance compute when it will reach or has reached a position where
too few signals can be received directly (i.e. without multi-path
distortion) from satellites SA1, SA2, SA3 in order to compute a
position with enough accuracy. In order to do this, the processor
unit PU is arranged to compute which satellites do not suffer
multi-path distortion, and which satellites do suffer multi-path
distortion. This computation is explained in more detail below.
Based on the outcome, the processor unit PU may decide to switch
from the first mode to the second mode, in which the relative
positioning system RPS is more emphasized.
[0124] Again the processor unit PU has knowledge of the current
positions of the satellites SA1, SA2 from which signals are
received (with or without multi-path distortion), as this
information is comprised by the signals (orbital information).
Using this information in combination with the shape and size of
geographical objects close to the latest determined position, which
is stored in the 3-dimensional digital map database 3DMD, the
processor unit PU can compute from which satellites signals can be
received without multi-path distortion by applying straightforward
geometry.
[0125] So, according to this embodiment, the positioning device PD
can predict, based on information from the 3D digital map database
3DMD that it will reach a position in which it is advantageous to
be in a certain mode (first mode or second mode). In response to
this, the positioning device PD may switch mode when this position
is about to be reached or has been reached.
[0126] Determining Quality of the Signals
[0127] As described above, the processor unit PU may be arranged to
determine which satellites SA1 are visible and which satellites SA3
are invisible or which satellites SA2 may suffer multi-path
distortion. The processor unit PU can compute this using
information about:
[0128] a) position of positioning device PD,
[0129] b) position of the respective satellite, and
[0130] c) 3D digital map database 3DMD.
[0131] The position of the positioning device PD used for computing
which satellites SA1, SA2, SA3 are visible, invisible or suffer
multipath distortion is the most recent position determined by the
positioning device PD, for instance in a previous position
determination. The position may also be an estimated position, i.e.
a position that is estimated to be reached in one second. This may
be done based on extrapolation of the velocity and direction of
movement, possibly in combination with map matching techniques and
using information about the planned route.
[0132] The position of the respective satellite SA1, SA2 can be
computed based on the orbital information as received from the
respective satellite SA1, SA2. Using this information, an elevation
angle .alpha. can be computed, which indicates under which angle
the respective satellite SA1, SA2 can be seen with respect to the
horizontal. It can also be determined in which direction .beta. the
respective satellite SA1, SA2 can be seen, for instance in a
westerly direction (270.degree. with respect to the northern
direction).
[0133] The 3D digital map database 3DMD is taken from a memory,
data carrier etc. as described above.
[0134] All this information can be used to compute whether or not
direct communication between the positioning device PD and the
satellite SA1, SA2 is possible and whether or not multi-path
distortion may occur using basic goniometric mathematics. It will
be understood that in case the positioning system is a terrestrial
system, the positions of the transmitters may be fixed and may be
known by the positioning device PD. In that case, their positions
only need to be determined once, and not repeatedly.
[0135] Also, the surface properties of the objects stored in the 3D
digital map database 3DMD (e.g. buildings) may be comprised in the
3D digital map database and used to decide upon the expected
intensity of multi paths.
[0136] Based on this computation, a measure for the quality of the
absolute position as determined by the absolute positioning system
APS can be computed and compared to a threshold quality. If the
quality of the absolute position as determined by the absolute
positioning system APS is below the threshold quality, the position
device PD may switch from first to second mode. If in second mode
and the quality of the absolute position as determined by the
absolute positioning system APS is above the threshold quality, the
position device PD may switch from second to first mode.
[0137] The quality of the absolute positioning system APS may be
determined by taking into account the number of satellites from
which direct signals may be received, their angle above the horizon
(low angled satellites usually provide relatively low quality
information), their spatial distribution over the sky.
[0138] This information may be used to switch from first mode to
second mode before the quality or accuracy of the position
determined by the first mode is likely to have decreased too much,
e.g. has decreased below a predetermined threshold. Also, this
information may be used to switch from second mode to first mode
when possible.
[0139] Flow Diagram 2
[0140] FIG. 4 schematically depicts a flow diagram depicting
actions as may be performed by the positioning device PD or the
processing unit PU according to an embodiment.
[0141] In a first action 200, the positioning device PD may start
executing the flow diagram as described here. The start may be
triggered manually by a user or may for instance be triggered by
switching on the positioning device PD.
[0142] In a second action 201, the positioning device PD determines
its position in the first mode, as schematically depicted in FIG.
4.
[0143] Once a position is determined, the positioning device PD may
compute the quality of the absolute positioning system APS for that
position. This is done in an action 202. For performing this
action, input from the 3-dimensional digital map database 3DMD of
geographical objects is used, in combination with the positions of
the satellites SA1, SA2 applying straightforward geometry.
[0144] In a next action 203, the computed quality of the position
determined based on the absolute positioning system APS is compared
to a threshold quality.
[0145] If the quality is high enough in action 204 it is decided to
return to action 201 and determine an updated position in the first
mode. If the quality is too low, in action 204 it is decided to
proceed to action 205 and determine an updated position in the
second mode.
[0146] After action 201 and 205, actions 202, 203 and 204 are
executed. This ensures that the positioning device PD automatically
switches from the first mode to the second mode and vice versa when
necessary and possible.
Embodiment 3
[0147] According to a further embodiment, the positioning device PD
may be arranged to keep a history file comprising the determined
positions and associated accuracies as determined according to the
absolute positioning system APS as well as the measurements
determined by the relative positioning system RPS.
[0148] For instance, the positioning device PD may be arranged to
keep a history file over a certain distance, e.g. the last 200
metres. Or, the positioning device PD may be arranged to keep a
history file during a certain time interval, e.g. the last
minute.
[0149] This history file may be used when switching from the first
mode to the second mode. Since the second mode more heavily relies
on information from the relative positioning system RPS, the
accuracy thereof heavily depends on the position that is used as
starting position for the relative positioning system RPS.
[0150] When switching from the first mode to the second mode, the
positioning device PD may be arranged to check the history file and
select, based on information comprised by the history file, which
position is to be used as starting position for the second
mode.
[0151] For instance, in case the accuracy of a first position
determined 50 metres before the switch has a very high accuracy and
a second position determined close to the switch (e.g. 5 metres)
has a very low accuracy, it may be more accurate to use the first
position as a starting position and not the second position,
although this second position is much closer to the position of the
switch from first to second mode.
[0152] In order to use this first position as a starting position,
it is necessary for the positioning device PD to also have stored
the measurements of the relative positioning system RPS in between
the first position and the position of the switch, to be able to
compute further positions in the second mode.
[0153] It will be understood that the positioning device PD may be
arranged to only keep a history file if a geographical object that
may result in a switch is approached. The positioning device PD may
compute if such a geographical object is approached based on
extrapolation of velocity and direction or based on a planned
route.
[0154] Flow Diagram 3
[0155] FIG. 5 schematically depicts a flow diagram that may be
performed by the positioning device PD to perform the embodiment
described here.
[0156] In a first action 300 the flow diagram is started. In a next
action 301 it is determined if a geographical object is approached
that may cause a switch between modes. If not, the positioning
device PD returns to action 301. If so, the positioning device PD
starts keeping a history file in action 302.
[0157] In action 303 it is determined if the positioning device PD
switches from first mode to second mode. If no switch is made
within a predetermined time interval or travelling distance, the
positioning device PD returns to action 303.
[0158] If a switch is made from first to second mode, in action 304
the positioning device PD determines what the best starting
position is for the relative positioning system RPS.
Embodiment 4
[0159] As described above, the geographical objects may be used to
decide when to switch between first and second mode. These
geographical objects may correspond to a real-life object that may
influence the absolute positioning system APS, such as a tunnel,
building, tree, hill etc.
[0160] The geographical objects (also referred to as geographical
points) may also be a position of which it is known that one mode
is to be preferred above the other, and the position does not
necessarily correspond to or is linked to a real-life object such
as a tunnel, building, tree, hill etc.
[0161] According to an embodiment, the positioning device PD is
arranged to add geographical objects to the digital map database
DMD based on measurements by the absolute and relative positioning
system and associated accuracies in the past. According to such an
embodiment, the positioning device PD is arranged to compute and
log the accuracies of determined positions and the mode in which
the positions were determined.
[0162] If it is detected that the accuracy of a determined position
or range of positions (e.g. in a tunnel), for instance in the first
mode, is below a certain threshold, this position may be stored as
a geographical object, with an advised mode (e.g. the second mode)
associated with it. The positioning device PD may also be arranged
to store such a position as a geographical object with an advised
mode assigned to it, only if the determined accuracy of the
determined position in one mode is below the threshold more than a
predetermined number of times (e.g. 5 times) or more than a
predetermined percentage of time (e.g. more than 50% of the cases
the position is determined).
[0163] This embodiment provides a self-teaching positioning device
PD that may add positions to the digital map database DMD or three
dimensional digital map database 3DMD of which it is known based on
previous measurements that determining a position in a certain mode
will most likely result in a relatively low accuracy, and the
positioning device PD may therefore switch to another mode before
such a position is reached. This may result in more accurate
positioning.
[0164] The measured accuracy information can be linked to the
digital map database DMD/3DMD and fed back to a map provider to be
included in newer generations of the digital map database DMD/3DMD
or broadcasted to a service provider to be distributed back to new
users. Also, the information can be broadcasted directly to users
in the vicinity to be shared between drivers. So, other drivers
which are not aware of future drop outs of absolute position
systems (tunnels, power lines) can learn about this and take
necessary precautions: switch to the second mode.
[0165] The information can be put back in the digital map database
DMD by a map provider or be distributed on the fly to a service
centre who then distributes it to other drivers. Also, this
information can be broadcasted directly to vehicles in the
neighbourhood who may store the information in their local digital
map database DMD for further use as described above.
[0166] Further Remarks
[0167] In both embodiments described above, switching from the
first mode to the second mode, and vice versa, is decided based on
a previously determined position in combination with information
stored in the digital map database. According to an embodiment,
also information about the position of satellites may be used.
[0168] It will be understood that although the embodiments above
describe a positioning device PD using a first and second mode, the
positioning device PD may further be arranged to work in further
modes, such as a third, fourth etc. mode. In these further modes,
the weighting of the absolute and relative positioning systems may
be different than in the first and second modes. Also, modes may be
different in that a different set of relative positioning systems
RPS are used. For instance, in the second mode, the positioning
device PD may use a compass and a velocity meter, where in the
third mode, also an accelerometer is used. It will be understood
that all kinds of variations are possible.
[0169] Therefore, it will be understood that the positioning device
PD may also be arranged to switch between the first, second and
further modes based on the determined position in combination with
information stored in the digital map database (DMD, 3DMD).
Geographical objects may also have an advised mode associated with
them, indicating to which mode the positioning device PD is to
switch when approaching such a geographical object.
[0170] The information stored in the digital map database DMD, 3DMD
that triggers the switch from first to second mode or vice versa,
may also comprise a time parameter, indicating that the switch
should only be made at certain moments in time. For instance, the
presence of leaves on trees may block receipt of signals for use by
the absolute positioning system APS only from spring to autumn, or
from spring to summer.
[0171] It will be understood that although the above embodiment are
presented as separate embodiment, combinations may be employed to
practice.
[0172] It will be understood that the embodiments as described here
may be provided as a computer program that, when loaded on a
computer arrangement, is arranged to perform any one of the
embodiments described above. Such a computer program may be
provided on a data carrier, such as a computer readable medium,
e.g. a floppy disk, a memory card, a CD, a DVD, etc.
[0173] For the purpose of teaching the invention, preferred
embodiments of the method and devices of the invention were
described. It will be apparent for the person skilled in the art
that other alternative and equivalent embodiments of the invention
can be conceived and reduced to practice without departing from the
true spirit of the invention, the scope of the invention being only
limited by the annexed claims.
* * * * *