Constant map matching, function

P82.61-0227-08

GPS satellite position finding

Illustrated on model 210

Basic position finding using compass direction (compass) and distance traveled (speed sensor).

Map-assisted position finding
(map matching)

General
Constant position finding is performed by calculation of the current vehicle position in the navigation processor. It is active when the ignition is switched on. During the switch-on phase (software loading phase) only the basic position finding is available. After switching off the ignition all important location parameters are stored in a non-volatile memory.

Basic position finding (dead reckoning):
The position is calculated in the navigation processor using the data from the front left axle VSS sensor (L6/1), the front right axle VSS sensor (L6/2), the reverse signal and the electronic compass. Dead reckoning is the basis function for continuous position finding. It is performed continuously and is independent of the CD-ROM map.

Map-assisted position finding (map matching):
Map matching serves for correcting the position obtained by dead reckoning in the digitalized map area. If the calculated position of the vehicle deviates from the map, it can be corrected on the basis of the map data.

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GPS position finding
The global positioning system (GPS) control module calculates the position of the vehicle (positioning accuracy approx. 100 - 300 m) using signals from at least 4 simultaneously received satellites.
When the position from dead reckoning is outside of an uncertainty window calculated by the navigation processor (depending on the number of satellites received), or when the navigation processor evaluates the position determined by dead reckoning to be less precise than the GPS position, the current position is corrected in the navigation processor with the aid of the GPS data.

Entry into map area
Upon entry into the CD-ROM map area the possible streets on which the vehicle may be located are determined by the navigation processor with the aid of the GPS position and the GPS uncertainty window.

Driving outside of CD-ROM map
Outside of the CD-ROM map (outside of country) position finding is accomplished only by dead reckoning corrected by the GPS data. The message "NO MAP" appears on the display.

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