You don't need to do any geometry. Your GPS module will simply output the speed.
While you can calculate based on position fixes, it is more accurate for the GPS to do it. It does not do a simple distance/time calculation but can instead look at the phase / doppler shift of the GPS signals. This ends up being much more accurate.
While you can calculate based on position fixes, it is more accurate for the GPS to do it. It does not do a simple distance/time calculation but can instead look at the phase / doppler shift of the GPS signals. This ends up being much more accurate.