On 2006-06-11, David W wrote:
"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..."

Well, in a light plane cruising between 4,000 and 8,000 feet, my
handheld Garmin 195 reports an estimated position error of 13 feet -
about 4 metres. Your friend doesn't know what he's talking about.

The map is only optimized for aviation in that it depicts airspace - the
receiver itself and the way it generates the map is no different from a
GPS for use by sailors or drivers or hikers.

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