Autocalibration of an electronic compass in an outdoor Augmented Reality system

Accurate registration in an Augmented Reality system requires accurate trackers. An electronic compass can be a valuable sensor in an outdoor Augmented Reality system because it provides absolute heading estimates. However, compasses are vulnerable to distortion caused by environmental disturbances to Earth's magnetic field. These disturbances vary with geographic location and are not trivial to model. Static calibration methods exist but these require an explicit initial calibration step and do not adapt to changing distortion patterns. This paper describes in detail an autocalibration method that compensates for changing compass distortions. With minimal user input, it automatically measures and adjusts the calibration table used to correct the compass output. Autocalibration uses redundant heading information computed from rate gyroscopes. We demonstrate that autocalibration converges to solutions similar to a distortion table that was manually measured with a mechanical turntable. With autocalibration, an electronic compass can provide useful measurements even as the user walks around through areas of varying magnetic distortion.