GF82.95-P-3000P Position Finding, Function

GF82.95-P-3000P Position Finding, Function

MODELS 203, 210, 220 up to 31.8.03
- with CODE (855) TELE AID
- with CODE (930) Taxi emergency call
MODELS 208.3, 215 up to 31.8.03
with CODE (855) TELE AID

The global positioning system (GPS) is a satellite-supported location finding system set up by the US Department of Defense. It is a toll-free service available throughout the world. 26 satellites are currently orbiting the earth on 6 different trajectories. The GPS satellites continuously transmit time and position data (longitude/ latitude).

Position finding
The vehicle location is determined parallel with two methods supplementing each other. The methods are called GPS location finding and basic location finding (dead reckoning).

GPS location finding:
GPS localizing is irreplaceable, especially in the case of journeys outside of the digitalized map area and after vehicle transportation (e.g. by train, ferry or towing).

A repeated GPS location finding (following satellite reception interruption) can take several minutes (up to 20 minutes when the unit is initially started up).

The computer and the GPS receiver unit are integrated in the D2B telephone and TELE AID transmitter/receiver (A35/17). If signals from at least 3 satellites have been received by the GPS antenna (A2/23) (model 203, 215), (A2/49a2) (models 208, 210, 220), the position and accuracy of the receiver location (vehicle) can be calculated.
Moreover, the direction of motion is determined with the aid of the sequence of the locations calculated with GPS. Parallel to the GPS location finding, the basic location finding takes place.
For the basic location finding of the vehicle, the D2B CTEL and TELE AID transmitter-receiver (A35/17) requires the following information:
- the signals from the left (L6/1) and right (L6/2) wheel speed sensors that have been prepared by the traction system control unit (N47). The number of impulses from the left front wheel speed sensor (L6/1) is a measure for the distance traveled.
- the data in the yaw rate sensor (gyro sensor) integrated in the D2B telephone and TELE AID transmitter/receiver (A35/17). The D2B telephone and TELE AID transmitter/receiver (A35/17) calculates the vehicle alignment (compass point) from the gyro sensor data.
- The data on the direction of travel
The reverse lamp signal indicates whether the vehicle is moving forward or backward.

Basic position finding is constantly carried out by the D2B telephone and TELE AID transmitter/receiver (A35/17) with "circuit 15R: ON" (once per second). The momentary vehicle position (longitude/ latitude) is calculated from the path traveled under consideration of the vehicle alignment and direction of motion.
If the computer calculates that the basic location finding is less precise than the GPS location finding, the currently calculated position is corrected with the aid of the GPS data.
In case of an accident the D2B telephone and TELE AID transmitter/ receiver (A35/17) automatically generates an emergency call telegram containing the vehicle's position data and transmits it via the vehicle's mobile telephone system (D-network).
The emergency call signal reaches the service provider.
With the available equipment (graphic-capable workstation and electronic road database), it is possible to determine the precise location of the vehicle with the aid of the position data.

Errors with basic position finding
Rolling backwards without the reverse gear engaged is evaluated as forwards motion, and may lead to a temporary error in map matching. Rolling with ignition switched off or vehicle transportation also falsify the position finding. In both cases the deviation is corrected automatically by the computer in the D2B telephone and TELE AID transmitter/receiver (A35/17) when GPS data are received.