Basic Location Finding

Basic location finding (dead reckoning) is the basic function of the continuous location finding feature. It is accomplished continuously when the ignition is switched on by the navigation processor and is independent of the data on the CD ROM map. After switching off the ignition the current position is stored.

The following information is calculated with the aid of basic location finding:
- Distance travelled,
- direction of motion (forwards or backwards)
- vehicle direction.


NOTE: Basic location finding is accomplished approx. once per second.


Distance traveled
The navigation processor receives the signals from the right front wheel speed sensor (L6/2) over discreet leads (not CAN bus) from the traction system control module (N47).
Evaluation of the wheel speed signals provides the distance traveled.

Direction of motion
The backup signal (from CAN passenger compartment bus) allows the navigation processor to recognize the direction of motion (forward or backward).

Vehicle direction
The direction in which the vehicle is pointing (compass direction) is calculated from the data of the gyrosensor and the sequence of locations calculated with the GPS by the navigation processor. The difference between the calculated and actual distance traveled between two turning points is used for automatic recalibration of the tire circumference (required due to tire wear).

Location finding errors with basic location finding
Rolling backward without the transmission shifting into reverse is evaluated as forward motion and can lead to an error in location finding.
Rolling with the ignition switched off or transport of the vehicle results in a location finding error.

However, the calculated position is automatically corrected by the navigation processor when GPS data is received.

Calibration
Calibration is required following tire change. This requires entry of the tire size, e.g.:

- 225/060/016

and coding whether

- new tires (tread depth approx. 5-10 mm), or
- used tires (tread depth approx. 3-5 mm)

The data is entered with Star diagnosis or directly on the COMAND operating, display and control module (A40/3). A special calibration drive is not required.