steve writes:

Doesn't the GPS give you 'altitude' -- computed as height above the
surface of an ellipsoid? Or does it correct for mean sea level? There
seem to be several computations required to derive true altitude from
the raw GPS altitude coordinate and it is not clear to me if
particular GPS receivers perform this adjustment.

I think that most of them use WGS84, which is a little more complex
than a simple ellipsoid.


All the best,


David