Map-Matching Algorithm of GPS Vehicle Navigation System
Pen -Shan Hung , Tsui -Chuan Su
Geographic Information System Research Center, Reng Chia University
100 Wenhwa Rd . Taichung, Taiwan
Tel : (886)-4-4516669, Fax : (886)-4-4519278
E-mail : tcu@gis.fcu.edu.tw
Abstract :
In general , Global Positioning System (GPS) has been widely used in Vehicle Navigation Systems. It helps the users to determine the vehicle position or provides users with proper maneuver instruction .Because of some biases, such as SA effect, buildings canyon around cities , thus those affect and block GPS signals .In addition , the road network of the digital Map is not accurate enough. These cause vehicle position not to locate precisely on the road network of the digital map. Therefore a map-matching algorithm is necessary. An optimal algorithm is developed through the analysis of some driving conditions (such as turning. U- turn or drive to parking lots).The algorithm is presented.
Instroduction
In vehicle Navigation System , Map- Matching approach plays an important role (Cring and Drane , 1994; Zhao,1997). It is a method of using digital map data and GPS satellite signal to locate the vehicle on proper poison relative to digital map.
In general ,the vehicle location is not necessarily on the road of digital map. We try to filter the unreasonable GPS signals and remove the biases of GPS signals by using map- matching system .We expect to find the stability of GPS signals from many tests for different receivers. Sometimes the vehicle location is compatible with the road network and it is not sometimes. Therefore ,it is possible to display vehicle location on the wrong road.
First, this paper describes the factor of noise that happens in the GPS positioning process.
Then, we develop a map-matching mode by programming and testing. Finally ,we hope to find out a proper algorithm to establish a trust and correct position system and hope to find out a proper algorithm can be used on the car navigation system easily.
Map-Matching Algorithm
Because of inaccuracy of GPS posting, we need to find the stability of GPS positioning for the receiver we used.
DV is the difference between the perpendicular distance point (V
n) at epoch n to road line and the distance of the point (V
n-1)at former epoch. Different GPS recever has different RMS values. Figure 1 demonstrates vehicle tracks with furno's GPS chip, and Figure 2 indicates the RMS valu for the receiver. The RMS value can Represent as the Stability of GPS receiver .
Fig. 1 Vechicle tracks with Furuno receiver
Fig.2 RMS value of the Furuno receiver.
Because of the SA effect and some other, positioning error estimated to be 30-100 meters. Although the positioning error is over 30 meters, the error difference between two sequent epochs is much smaller than 30 m. For the first epoch, the position bias can be determined by comparing the road central line with the vehicle location. The derived position bias can be first used to correct GPS position for the following epochs. The above derived RMS value is used to decide whether the vehicle is on the road or away from the candidate road (or heading for parking lots). If the vehicle is away from the road, then the vehicle location does not necessarily to match on the road of digital map.
