Using a GIS road network to improve GPS positions

Today most current road navigation systems depend heavily on the positional information provided by GPS. GIS maps are becoming more accurate and reliable as high resolution images from satellites and aircrafts are frequently used to update GIS maps. When the GPS positional information is used in conjunction with these GIS digital maps, many mismatch situations occur whereby the location of the user is mistakenly shown to be on a nearby road. The main cause for these mismatch situations is that GPS can only provide about 10∼30m accuracy. Current real-time differential GPS (DGPS) is able to provide more accurate positions (1∼5m). However, DGPS also needs the establishment of prohibitively expensive reference stations to transmit DGPS correction data. The required number of broadcasting stations needed to create a useable communication network also becomes inefficiently expensive especially in sparsely populated regions. (This is due to the poor strength of the communication media used to transmit the DGPS correction data.) Therefore, very few commercial road navigation systems use DGPS as the position providing platform. In this study we integrate the GPS module that can provide the GPS raw data with a GIS digital road map to create a Virtual Geographic DGPS (VDGPS). In theory, such that system can provide position data as accurate as the real DGPS, so the digital road map of specific feature points is used for reference stations to correct the GPS pseudoranges. In order to provide the correct way to the position from VDGPS will be used to carry out the methods with the center road lines, turning nodes and corners. An experiment is tested to evaluate and analyze the proposed method, the position data from the proposed method compares with the dual-band highly accurate GPS receivers (1∼2cm). The result indicates that method can provide the position data as accurate as DGPS.