GF82.61-P-3007RA Global Positioning System MAP Matching, Function

GF82.61-P-3007RA Global Positioning System Map Matching, Function
- with CODE (352) COMAND operating and display system
- except CODE (491) USA version
- except CODE (498) Japan version






The global positioning system (GPS) is a location finding system established by the US Defense Department and is satellite supported. It is not subject to fees and is available worldwide. Presently 26 satellites are present in six different orbits. The GPS satellite constantly transmit time and position data.

4 satellites are needed for the first position calculation, after this three receivable satellites are sufficient.
GPS localizing is irreplaceable, especially in the case of journeys outside of the digitalized map area and following vehicle transportation (e. e. train, ferry and towing).
A repeated GPS location finding (following satellite reception interruption) can take several minutes (when the unit is initially started up to 20 minutes).

GPS map matching, function
The navigation processor in the COMAND operating, display and control module (A40/3) calculates the vehicle location and the exact position from the satellite signals received and amplified by the GPS antenna (A2/23).

The actual calculation is essentially based on measuring the runtimes of the synchronously transmitted signals from the different satellites. One important prerequisite is that the clocks of the satellites and the receiver be synchronized.

For this purpose, the receiver has an automatic time correction feature which again is possible with the aid of the satellite signals. When the navigation processor determines that the basic location finding is less precise than GPS location finding, the current calculated position is corrected with the aid of the GPS data. Moreover, the route of the vehicle is determined from the sequence of locations calculated with GPS.

The location is recalculated approx. 50 times per minute by the GPS system.

Possible interference in reception of GPS signals:
As GPS operates in the GHz range (microwaves) and the signals are weak, reception interference may occur due to:
^ Atmospheric interference
e. g. weather, water vapor, mist
^ Multipath reception due to the reflection of the signals,
e. g. on house walls
^ Signal shading
e.g. in built-up areas, tunnels, high buildings, trees

GPS reception therefore necessitates a clear view of the sky. Positioning accuracy is approx. 100 m or higher.