Process for establishing the driving direction of a vehicle with an electronic compass

Process for determining the driving direction of a motor vehicle including an electronic compass provided with a fixedly mounted magnetometer, said magnetometer having a plurality of probes arranged along mutually perpendicular axes to define a vector diagram and generating electrical signals depending on magnitude and direction of magnetic field present at said magnetometer, an evaluation circuit including a computer and storage means, said signals being applied to said evaluation circuit to determine the direction and magnitude of an interference magnetic field, the earth's magnetic field and the driving direction of the vehicle, the process comprising the steps of at least partially turning the vehicle, applying to said evaluating circuit the signals pertaining to at least five measuring points measured during the turning and storing said signals in the storing means;

• processing in the computer the stored signals according to an algorithm having at least five unknowns to compute the center point displacement, the shape and the turning of the local curve of the earth's magnetic field in the vector diagram;
• aligning the vehicle with a predetermined cardinal direction (east) and subtracting the angle .phi..sub.o between the cardinal and the north directions from the angle .phi.' of the earth's magnetic field indicated by the electronic compass to produce a correction angle .DELTA..phi.;
• storing the correction angle in the storage means;
• and
• subtracting or adding in the computer said stored correction angle from or to a driving direction computed from measuring signals produced during subsequent measurements by said magnetometer.