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 NAVIGATION SYSTEM USING POSITION NETWORK FOR MAP MATCHING
 Inventor: Upparapalli Karunanidhi, Troy, Mich.
 Assignee: Magellan DIS, Inc., Rochester Hills, Mich.
 Appl. No.: 09/056,218  Filed: Apr. 7, 1998
 Int. CI.7 G06G 7/78; G01C 21/00
 U.S. CI 701/208; 701/210; 701/214;
 Field of Search 701/201, 202,
701/207, 208, 209, 210, 211, 212, 205, 213, 214, 216, 220, 221; 707/100, 2; 340/988, 990, 995; 345/473; 342/451, 357.01, 457;
 References Cited
U.S. PATENT DOCUMENTS
5,046,011 9/1991 Kakihara et al 701/209
5,109,344 4/1992 Kakihara et al 701/209
5,307,278 4/1994 Hermans et al 701/217
5,371,678 12/1994 Nomura 701/210
5,465,089 11/1995 Nakatani et al 340/995
5,613,055 3/1997 Shimoura et al 701/200
5,648,901 7/1997 Gudat et al 701/23
5,657,226 8/1997 Shin et al 701/23
5,684,696 11/1997 Rao et al 701/25
5,774,824 6/1998 Streit et al 701/307
5,978,732 11/1999 Kakitani et al 701/211
5,982,301 11/1999 Ohta et al 701/210
FOREIGN PATENT DOCUMENTS
0339639 of 1989 European Pat. Off. .
Primary Examiner—-Jacques H. Louis-Jacques
Attorney, Agent, or Firm—Howard & Howard
A navigation system includes a positions network having a plurality ol nodes, each corresponding to a segment in a road segments network. A branch is propagated from each node in the positions network based upon a dead reckon path ol position vectors. Each ol the branches in the positions network represents a potential current position ol the vehicle. The branches in the positions network are compared to the segment in the segments network to determine a current position ol the vehicle.
16 Claims, 2 Drawing Sheets
NAVIGATION SYSTEM USING POSITION
NETWORK FOR MAP MATCHING
BACKGROUND OF THE INVENTION
The present invention relates to navigation systems and more particularly to a navigation system having an improved system and method for determining current position utilizing map matching.
Current navigation systems include one or more sensors for propagating the position of a vehicle. A sensor for determining displacement, such as a wheel speed sensor, is used in conjunction with a sensor for determining heading, such as a gyro, to generate a series of position vectors. The position vectors generally include a displacement and a heading. The series of position vectors forms a "dead reckon" path of the vehicle.
Generally, by periodically determining the position vectors of the vehicle, the navigation system can dead reckon the current position of the vehicle by utilizing "map matching". The navigation system includes a database of road segments, including segment length and intersection points. After receiving each new position vector, the navigation system compares the shape of the dead reckon path to the shape of the road segments in the database. The navigation system determines the current position of the vehicle by comparing the shape of the dead reckon path with the road segments in the database. After each new position vector is received, the navigation system compares the shape of the dead reckon path to all the potential road segments on which the current vehicle may be.
Near a node, or intersection, the navigation system may have to compare the shape of the dead reckon path to numerous road segments after each new position vector is received. This reduces the efficiency and speed with which the navigation system can rule out road segments and determine the current position of the vehicle relative to the road segments in the database.
SUMMARY OF THE INVENTION
A navigation system of the present invention determines the current position of the vehicle more quickly and efficiently by utilizing a positions network of potential current positions.
The navigation system of the present invention includes sensors for generating a dead reckon path comprising a series of position vectors each having a heading and a displacement. A database of roads to be traveled by the vehicle includes a segment network of road segments intersecting at nodes. A positions network is generated having a plurality of nodes each corresponding to a node in the segments network. A branch is propagated from each node in the positions network based upon the position vectors. After each position vector is received, each branch of the positions network is compared to a corresponding road segment in the segments network. Preferably, a cumulative total of the angular deviations (weighted by displacement) between each branch in the positions network is compared with the corresponding segment in the segments network.
The navigation system determines that the current position of the vehicle is where the branch in the position network has the lowest cumulative angular deviation from its corresponding segment in the segments network. If the cumulative angular deviation for a branch in the positions network exceeds a predetermined threshold, that branch is "pruned" and no longer propagated or compared to the segments network.
Since a plurality of possible position branches are generated in the positions network, each corresponding to a segment in the segments network and since the angular deviation is accumulated and evaluated after each position
5 vector is received, the current position of the vehicle is more efficiently and quickly calculated. The navigation system can more quickly determine the current position of the vehicle because it has been propagating a plurality of positions branches and has been comparing each of them to
10 the segments network after receiving each position vector. At or near a node in the segments network, the navigation system does not have to compare the entire shape of the dead reckon path to each of the potential paths in the road segment network. As a result, the navigation system can
15 more quickly determine the current position of the vehicle and more quickly prune branches from the positions network.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
FIG. 1 is a schematic of the navigation system of the present invention;
FIG. 2 illustrates the positions and segments networks of the navigation system of FIG. 1; and 30 FIG. 3 illustrates the positions and segments networks of FIG. 2 as tree data structures.
DETAILED DESCRIPTION OF THE
The navigation system 20 of the present invention is shown schematically in FIG. 1. The navigation system 20 includes a CPU 22 connected to a display 24, such as a high resolution LCD or flat panel display. The CPU 22 is also connected to an input device 26 such as a mouse, keyboard, key pad or remote device. Alternatively, the display 24 can be a touch screen display. The navigation system 20 further includes a storage device 28, such as a hard drive 28 or CD ROM, connected to the CPU 22. The storage device 28
45 contains a database including a map of all the roads in the area to be traveled by the vehicle 32 and may contain the software for the CPU 22, including the graphical user interface, route guidance, operating system, positiondetermining software, etc.
50 The navigation system 30 preferably includes position and motion determining devices, such as a GPS receiver 34, a gyroscope 36, a compass 38, a wheel speed sensor 40 and an orthogonal multiple axis accelerometer 41 all connected to the CPU 22 (connections not shown for simplicity). Such
55 position and motion determining devices are well known and are commercially available.
The navigation system 20 determines the position of the vehicle 32 relative to the database of roads utilizing the position and motion determining devices. The driver selects
go a destination relative to the database of roads utilizing the user input device 26 and the display 24. The navigation system 20 then displays turn-by-turn instructions to the driver to guide the driver to the desired destination from the present position.
65 FIG. 2 illustrates how the navigation system 20 determines the present position of the vehicle 32. The database includes a plurality of road segments intersecting at segment