Global Positioning System Location Finding

General
The global positioning system (GPS) is a satellite-supported location finding system set up by the US defense department. It is not subject to fees and is available worldwide. Presently 26 satellites in 6 different orbits are used. The GPS satellites continuously transmit time and position data. When data from at least 3 satellites can be received (for two-dimensional location finding), the position of the receiver can be calculated.

GPS location finding is invaluable particularly when traveling outside of the digitalized map area and following vehicle transport (e.g. train, ferry or towing). Calculation of the new location with GPS (after interruption of the satellite reception) can take several minutes (up to 20 minutes when equipment is first operated).

Since GPS operates in the GHz range (micro-wave range) and the signals are weak, reception interference can result from:
- Atmospheric interference,
e.g. weather, water vapor, fog

- Multiple reception
resulting from reflection of signals, e.g. from building walls

- Signal shadows.
e.g. in roofed-over areas, tunnel, high buildings, trees.

A free view of the sky is required for GPS reception. The locating accuracy is approx. 100 m or better.

GPS location finding - function
The navigation processor (A40/3n2) calculates the vehicle location and accuracy of the location from the satellite signals received by the GPS antenna (A2/49a2) and amplified. If the navigation processor (A40/3n2) determines that the basic location finding is not as precise as the GPS location finding, the currently calculated position is corrected with the aid of the GPS data. Moreover, the direction of motion of the vehicle is determined with the aid the sequence of locations calculated with GPS.