Basic map matching function - GF82.61-P-3006E

MODEL 208, 210 with CODE (352a) COMAND operating and display system

S=mileage covered

Fig 1: Identifying Basic Map Matching Function

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Basic map matching (composite positioning) is the basic function of constant map matching. This is carried out constantly by the navigation processor when the ignition is switched on, and is not dependent on the CD-ROM map. The current position is stored after the ignition is switched off.

The following information is calculated with the aid of basic map matching :

Mileage covered,
Direction of travel (forwards or backwards) and
Vehicle orientation.
Basic map matching is carried out approx. 1x per second.

Mileage covered

The navigation processor receives the signals output by the front right wheel speed sensor (L6/2) from the traction system control module (N47) via discrete leads.

The evaluation of the wheel speed signals reveals the mileage covered.

Direction of travel

Via the signal for reversing (supplied via interior CAN), the navigation processor detects the direction of travel (forwards or backwards).

Vehicle orientation

From the data from the rate of rotation sensor (gyrosensor) and the sequence of the locations calculated with GPS, the navigation processor calculates the vehicle's orientation (points of the compass).

The difference in the calculated mileage and the mileage actually covered between two turn-off points is used to automatically recalibrate the tire circumference (necessary due to tire wear).

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.

In both cases, this deviation is automatically corrected by the navigation processor on receipt of GPS data.

Calibration

Wheel calibration is necessary following a tire change. In order to achieve this, it is necessary to input the tire size, e.g.:

225/060/016
and the code whether
new (depth of tread approx. 5-10 mm) or
used tires (depth of tread approx. 3-5 mm)

have been installed. Input is carried out via the STAR diagnosis tool or directly on the COMAND operating, display and control unit (A40/3) .

No special calibration journey is necessary.

Global Positioning System, map matching, function	GF82.61-P-3007D
Map-supported map matching, function	GF82.61-P-3008D
Destination guidance, function	GF82.61-P-3012E
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