On Wed, 21 Jul 2010 09:58:39 -0700 (PDT), Frogwatch
wrote:

My son has an Android and he turned the compass app on. I held it
near a steel object and I was amazed that it deflected as a magnetic
compass would. The built in compass is NOT GPS based but seems to have
a solid state flux gate sensor that responds to the earths mag field.

You can get a GPS based compass system from Furuno among others but
they require multiple GPS antennas seperated by some short distance.
They require no compensation or deviation tables, even on steel hulled
boats.

http://www.boatersland.com/sc50.html

Garmin makes several different handheld GPSs with built flux gate
compasses. I have their 400C but the fluxgate is only 2-axis which
requires that you hold it level to get an accurate reading.

DeLorme has a new GPS with a 3-axis fluxgate and you can couple it
with a SPOT satellite uplink module.

http://www.delorme.com/about/pressre...mmunicator.htm