On Friday, October 30, 2015 at 3:49:16 PM UTC-7, Andrzej Kobus wrote:
On Friday, October 30, 2015 at 5:43:43 PM UTC-4, wrote:
On Friday, October 30, 2015 at 2:20:55 PM UTC-7, Andrzej Kobus wrote:
I don't think there is such a thing as GPS compass, regardless if you are moving or not. GPS is measuring your position, it has nothing to do with measurement of magnetic field.

You can determine orientation (including direction) by using difference in 3D position of two GPS receivers (actually their antennae) mounted at a fixed displacement from each other. It's a bit more complicated than it sounds, as ideally, the two GPS receivers will have synchronized clocks and be using the same satellites for their position solutions. So, the receivers used are quite specialized.

You are right, with two receivers and antennas far apart to mitigate the errors it is possible. Not something that one would want to mount in an aircraft.

There are two types of GPS compasses I have seen (for boats). One has three antennas arranged in a triangle about 12 inches apart and does not use their GPS position, rather they measure signal delay and knowing the position of the satellite constellation determine orientation. They are quite accurate immune to deviation and motion errors. More common recently are the two GPS receiver versions that determine orientation by position. Furuno and Vector make them and probably others with claimed RMS accuracy of 0.5 deg. Less than $2K .