David,

GPS is optimised for sea level, Blanchefort [a mountaintop ruined
castle] is 467 metres above sea level, couple this with a slant range
to a satellite of several thousand miles and the curvature of the earth
and you have error. At least up to 100 metres..."


That's just plain BS. Just one example: The space shuttle uses GPS for
navigation. That should be plenty high to convince the poster otherwise.

--
Thomas Borchert (EDDH)