Location Finding, Function
Location Finding, Function
The global positioning system (GPS) is a satellite-supported location finding system set up by the US Department of Defense. It is free of charge and is available worldwide. 26 satellites are currently orbiting the earth on 6 different trajectories. The GPS satellites continuously transmit time and position data (longitude/latitude).
Location 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:
The GPS location finding is particularly valuable when driving outside of the digitized map area and following vehicle transport (e.g. train, ferry or towing).
A repeated GPS location finding (following satellite reception interruption) can take several minutes (when the unit is initially started up to 20 minutes).
The processor and the GPS receiver unit are integrated in the EMERGENCY CALL control module (A35/8). If signals are received from at least 3 satellites via the GPS antenna (A2/23), it is possible to calculate the position and the accuracy of the location finding of the receiver (vehicle) (positioning accuracy 100 m).
In addition, the vehicle's direction of travel is determined with the aid of the sequence of the locations calculated with GPS.
The basic location finding is determined parallel to the GPS location finding.
Basic position finding (dead reckoning):
For the basic location finding of the vehicle, the D2B CTEL and TELE AID transmitter-receiver (A35/17) requires the following information:
- the signals of the left front wheel speed sensor (L6/1) and right front wheel speed sensor (L6/2) processed by the ESP, PML and BAS control module (N47-5). The number of impulses from the left front wheel speed sensor (L6/1) is a measure for the distance traveled.
- The data of the gyrosensor integrated in the EMERGENCY CALL control module (A35/8).
the EMERGENCY CALL control module (A35/8) calculates the vehicle orientation (compass direction) from the data supplied by the gyrosensor.
- The data on the direction of travel
The reverse lamp signal indicates whether the vehicle is moving forward or backward.
- Signal of stop lamp switch (S9/1).
The basic location finding is performed by the EMERGENCY CALL control module (A35/8) with "circuit 15R: ON" (once per second). The momentary vehicle position (longitude/latitude) is calculated from the distance traveled taking into account the vehicle orientation and direction of travel.
If the processor determines that basic map matching is less precise than GPS map matching, then the currently calculated position is corrected with the aid of the GPS data.
In an accident occurs, the EMERGENCY CALL control module (A35/8) automatically generates an emergency call telegram which contains the position data of the vehicle and transmits this over the mobile phone system (GSM 900 MHz) of the vehicle. The emergency call signal is received by the service provider (e. g. Tegaron in the case of Tele Aid).
With equipment available there (graphic supported work station and electronic road data base) it is possible to determine the precise location of the vehicle with the aid of the position data.
Positioning errors in basic map matching
Rolling backwards without the reverse gear engaged is evaluated as forwards motion, and may lead to a temporary error in map matching. Rolling with the ignition switched off or vehicle transportation also falsify map matching.
The deviation is automatically corrected by the processor in the EMERGENCY CALL control module (A35/8) in both cases when the GPS data are received.
Location finding with GPS
Location finding with GPS:
Basic location finding (dead reckoning)
Basic location finding (dead reckoning):
