Map-Matching Algorithm of GPS Vehicle Navigation System
In general, the vehicle location is not necessarily on the road of digital map. According to the coordinates determined by GPS, the GPS derived coordinates has to be used to decide which road is candidate with high probability. For GIS-based digital map, a curve road is represented by many vertexes. It can't simply calculate perpendicular distance from GPS point to central line. Assuming that GPS point is GI with coordinate (X
G1, Y
G1), from-node of road is S1 with coordinate (X
S1, Y
S1), to-node of road is E1 with coordinate (E
E1, Y
E1). The value of K can be determined.
The (X
n, Y
n) are the coordinates of the projected point of the road:
XN=K*(XE1-XS1)+ X S1 ........................(4)
YN=K*(YE1-YS1)+ YS1........................(5)
2) If K < 0, then the vehicle location is not on the candidate road, and the location is away from the from-node S
1
3). If K > 1, then the vehicle location is not on the candidate road, and the location is away from the to-note E
1
Selecting an accurate candidate road is important, and it affects prediction of nest vehicle location.
Fig .3 a Muddy vehicle location
In Fig3, the candidate road of G1 is either line or line2. The possibility of making wrong decision is very high. To solve this problem we consider the vehicle traveling direction. In digital road map database the true azimuth of road is recorded, and NMEA data also includes the vehicle direction. Therefore, we can compare these two any try to select the candidate road.
