A satellite-based radio positioning finding system forms the basis of in-car navigation systems. This so-called Global Positioning System (GPS) was developed back in the early 1970s by the US defence ministry, original for purely military purposes. At the start of the 1990s, part of this system was released for civil use.
The GPS system can be used to determine a person's precise location in terms of longitude, latitude and altitude. The in-car navigation system receives these signals. At the same time the speedometer's velocity signal and the direct in which the car is travelling according to an electronic compass are included in the calculation to achieve greater precision.
Depending on version, the navigation system uses maps stored on CD or DVD - these are either geographic data or complete, graphic maps depending on version. Once a destination has been entered, the navigation computer integrated into the system calculates the quickest or shortest route to the destination from the vehicle's current location and, throughout the route guidance process, compares the calculated route with the vehicle's current position. If these do not coincide - because the driver has decided to take a different route to avoid a traffic jam, for example - an adapted route is calculated.
Dynamic route guidance is possible with the Traffic Message Channel (TMC). This enables the navigation system to recognise traffic congestion automatically and offer an alternative route.
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