During my endless search for digital compasses for use in a current project, I recently found a reference to an entirely original technique for sensing direction:
The discrete sensing elements employed in such sensor modules are generally called magnetometers and/or mango-inductive sensors.
(emphasis mine) I guess it senses the Earth’s mangetic field 😉
Seriously though, good/cheap/fast digital compasses are hard to find – I’ve been playing around with the Robot Electronics CMPS03, but it’s crazy power-hungry and not tilt-compensated. I’ve got some Honeywell HMC6343’s with breakout boards on the way, but the datasheet says they max out at 10Hz. I’ll probably just use accelerometers for fast movements, and calibrate continuously to the slower compass.