Re:Duh. (Score 1)

The GPS sigal can be used to compute attitude/direction. Instead of using the standard code phase offsets and doppler for position and velocity, the receivers also use carrier phase processing and multiple antennas. By computing time of arrival offsets of specific carrier phases at each antenna, the system can determine angle of arrival. Think of this as sort of a reverse direction finding procedure, with very accurate transmitter, atomic clock timing source, and precisely known position of the transmitter. Arrange the attennas properly, and you can obtain a very precise attitude along any or all axes of interest. Your basic handheld receivers don't do this. In general, these systems are specifically built to purpose and can run you a good penny.