Abstract: A method for converting distorted compass data values into corrected data values which employs linear transforms. A linear transform is formulated and programmed into the read only memory of the microcomputer of the electronic compass system. The microcomputer uses the linear transform to transform compass data readings distorted by ferrous metals in the environment of the vehicle into corrected data readings and then uses the corrected data readings to compute headings.

Abstract: A method for removing noise from data in an electronic compass system which discounts noise values or outliers (extreme headings far from average) by displaying median headings in the absence of a clear trend in the direction of change of sampled headings. If a clear trend is detected, extreme headings are displayed. Compass jitter is reduced by requiring two consecutive differences be on the same side of the displayed heading before the displayed heading is changed.

Abstract: A magnetic transient detection technique which alerts a microcomputer of an auto-calibrating compass when electrical transients which produce magnetic transients have occurred. The technique employs an electronic compass control circuit having a sampling rate high enough to isolate electrical transients from transients produced by normal motion of the vehicle. Accelerations in data values defined as the difference between two changes in the coordinates for the center of the earth's magnetic field circle, are calculated and compared to predetermined threshold accelerations. Previous acceleration values and their associated vehicle magnetic field vectors can be stored in the microcomputer. After a magnetic transient is detected, its associated vehicle magnetic field vector is subtracted from the resultant magnetic field to yield vehicle heading. Once detected, magnetic transients are also used to initiate auto-calibration.

Abstract: A method for selecting calibration data which uses mean square error to minimize variations in the calculated origins of the earth's magnetic field vector. A microcomputer having a memory calculates and stores the origin of the earth's magnetic field vector from the last three headings or data points. The x and y coordinates of the origins are summed with all the previous x and y coordinates and the mean square errors of the x and y coordinates are calculated. A figure of merit for the mean square errors is calculated. An adjusted origin is determined and stored by weighing the newly calculated origin by a figure of merit and adding it to the previous origin. Provision is made for reinitializing all quantities to zero when the sum of the mean square errors exceeds a predetermined maximum.