Appendix
Appendix
Positioning technology
Positioning by GPS
The Global Positioning System (GPS) uses a network of satellites orbiting the Earth. Each of the satellites, which orbit at a height of
21 000 km, continually broadcasts radio sig- nals giving time and position information. This ensures that signals from at least three can be picked up from any open area on the earth’s surface.
The accuracy of the GPS information depends on how good the reception is. When the sig- nals are strong and reception is good, GPS can determine latitude, longitude and altitude for accurate positioning in three dimensions. But if signal quality is poor, only two dimen- sions, latitude and longitude, can be obtained and positioning errors are somewhat greater.
Map matching
As mentioned, the positioning systems used by this navigation system are susceptible to certain errors. Their calculations may, on occa- sion, place you in a location on the map where no road exists. In this situation, the processing system understands that vehicles travel only on roads, and can correct your position by ad- justing it to a nearby road. This is called map matching.
Appendix
With map matching
Without map matching
Handling large errors
Positioning errors are kept to a minimum by combining GPS and map matching. However, in some situations, these functions may not work properly, and the error may become big- ger.
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