GF82.61-P-3006QM Basic Position Finding, Function

GF82.61-P-3006QM Basic Position Finding, Function
- with CODE (527) COMAND APS (with navigation)






Basic position finding (dead reckoning) is the base function in continuous position finding. It is carried out continuously by the navigation processor of the COMAND operating, display and controller unit (A40/3) when the ignition is switched on. The current position is stored after the ignition is switched off.

The following information is required for basic position finding (dead reckoning):
^ Travel distance covered
^ Direction of travel (backwards or forwards)
^ Vehicle course

Distance traveled
The navigation processor in the COMAND operating, display and controller unit (A40/3) receives the wheel speed signals from the ESP and BAS control unit (N47-5) via the Controller Area Network bus class C (engine compartment) (CAN-C) for calculating the distance traveled. The evaluation of the wheel speed signals shows the distance traveled.

Direction of travel
With the help of the signal for reversing that is transmitted by the EIS control unit (N73) through the Controller Area Network bus class B (interior) (CAN-B), the navigation processor of the COMAND operating, display and controller unit (A40/3) recognizes the direction of travel (forward or reverse).

Vehicle course
The navigation processor calculates the vehicle course from the data of the yaw rate and lateral acceleration sensor (B24/15) and the sequence of positions calculated using the global positioning system (GPS).

The difference in the calculated mileage and the mileage actually covered between 2 turnoff points is used to automatically recalibrate the tire circumference (necessary due to tire wear).

Position finding errors during basic position finding (composite positioning)
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 when the ignition is switched off or transporting the vehicle can also distort the position finding.
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. For this it is necessary to enter the tire size and the coding for the tread depth. The data are entered using STAR DIAGNOSIS or directly on the COMAND operating, display and controller unit (A40/3). A special calibration journey is not required.