How do hand-held GPSs know which way they’re pointing?
Many stand-alone hand-held GPSs (ie, those used by mountain walkers, or in light GA) give you a left/right steer to a waypoint.
I understand how GPS works out its present position. And I don’t have any difficulty with the idea of computing a great circle track from the present position to a waypoint.
But how does a stand-alone GPS, with no connection to aircraft avionics/compasses/INS/IRS, know which way it’s pointing? How does it know whether to turn you left or right until you’re steering towards the target?