We integrated the marvel mind indoor GPS with the Erle Rover but the heading is off. We tried to calibrate the compass but to no avail. The heading was accurate when we used the GPS that came with the Erle rover. However, once we went indoors (no GPS fix) the heading (compass) of the rover starts to act strangely (the compass direction is wrong and is off by around 10-20 degrees and maybe sometimes around 180 degrees) and the message "bad AHRS" appears.
I thought that the compass should point to an accurate position regardless whether it is indoors or outdoors and with or without the GPS. How should I go about to solve this heading issue?