GF82.61-P-3006RA Basic MAP Matching, Function

GF82.61-P-3006RA Basic Map Matching, Function
- with CODE (352) COMAND operating and display system






Basic location finding (dead reckoning) is the basic function of continuous location finding. This is performed by the navigation processor in the COMAND operating, display and control module (A40/3) continuously when the ignition is switched on and is independent of 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 location finding:
^ Distance travelled
^ Direction of motion (forwards or reverse)
^ Vehicle orientation

The basic location finding is carried out approx. once per second.

Distance travelled
Via the CAN engine compartment, the navigation processor receives the wheel speed signals from the traction systems control module (N47) and as of 1.7.02 from the ESP and BAS control module (N47-5).
The evaluation of the wheel speed signals reveals the mileage covered.

Direction of motion
The signal for backing up which is transferred by the EIS control module (N73) via the passenger compartment CAN bus, allows the navigation processor to recognize the direction of motion (forwards or backwards).

Direction in which vehicle is pointing
From the data provided by the gyrosensor) and the sequence of locations calculated with GPS, the navigation processor calculates the direction in which the vehicle is moving (compass direction). The difference in the calculated and actual distance travelled between two turning points is used to automatically recalibrate the tire circumference (required due to tire wear).

Errors with basic location finding
Rolling backwards without the transmission being shifted into reverse gear is evaluated as moving forwards and can lead to temporary errors in location finding.
Rolling with the ignition switched off or transport of the vehicle also make the location finding result erroneous. The deviation is corrected automatically in both cases by the navigation processor upon receiving GPS data.

As of 1.7.02 the direction of motion signal (forwards/reverse) is generated by the wheel speed sensors. This makes possible an exact recording of the distance traveled.

Calibration
Wheel calibration is necessary following a tire change. For this the coding and entry of tire size is important, e.g.:
^ 225/060/016
^ new tires (tread depth approx. 5-10 mm) or
^ used tires (tread depth approx. 3-5 mm)

The entry is accomplished with Star Diagnosis or directly at the COMAND operating, display and control module (A40/3). A special calibration drive is not required.