Map-Matching Algorithm of GPS Vehicle Navigation System
After selection of the candidate road, Shown in Fig. 4, We assume current vehicle location is in G
1, next vehicle location is G
2, if the distance between G
1, and E
1, (end-node of road segment) are close to a pre-set value, the next turning candidate road will be Line1, Line2 and Line3. G
1E, is the azimuth of traveling direction from G
1, to E
1, point, G
2E, is the azimuth from E
1, to G
2, point. These values of azimuth will be used for judging which road is the candidate.
If driver has a U-turn, the from-node and to-node of road segment must be switched. In Fig. 5, assuming current vehicle location is at G
1, point, the location of former epoch is G
0, endnode of road segment is E
1,
DHEADING = G
1a - G
0a
If
DDISTANCE is negative and larger then a tolerant value and
DHEADING > Tolerance, we presume, we presume vehicle has a U-Turn.
Fig. 4 Off-Road Segment Case.
Fig .5 U- turn Case
Analysis Results
A few typical road networks and different driving behavior have been tested for the map-matching method. They include simple road network, complicated road network, off-road driving, and U-turn driving etc. Figures 6 to 9 shows that the map-matching has not been tested for some other sophisticated 3-dimensional road networks, since this kind of digital map for 3-D road network is not available yet. The further test is required.
Fig.6 Simple Road Case
Fig .7 Complicated Road Case
Fig.8 Off-Road Driving Case
Fig.9 U-turn Driving Case
Conclusion
A simple map-matching algorithm is successfully used project the vehicle location on the digital map 2-dimensional road network. Within the algorithm, the stability is determined and used to judge whether the vehicle is still on the candidate road or off the candidate road to parking lots. In additions, the traveling direction and the change of vehicle heading are also taken advantage of.
We can also use DGPS technology to reduce the GPS positioning error. DGPS should make the map-matching easier. However, vehicle has to be equipped with radio-modem. This will increase the cost to set up the data-link system
References
-
Craig A. Scott and C.R. Drane(1994), Increased Accuracy of Motor Vehicle Position Estimation By Utilizin Map Data, Vehicle Dynamics, and other Information Sources, proceeding of Vehicle Navigation and Information Systems.
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Craig Scott (1994), Impoved GPS Positioning for Motor Vehicles Through Map Matching, Proceeding of Ion GPS-94, Salt Lake City, Utah, pp. 1391-1400
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Yilin Zhao (1997), Vehicle Location and Navigation System, Artech House, pp. 83-103.
