This is missing a little bit of input validation, e.g. we don't
currently check that set_position azimuth and elevation are actually
in the range that the controller can possibly move.
The geodetic north offset configuration value is applied in when
computing the current position, but I think there are still some
slightly fiddly edge cases around it and I haven't actually figured
out which direction I want the sign to be.
The various pieces appear to be functional, so next up will be figuring
out what all the problems are with some hardware in the loop.
