GPS altitude vs altimeter altitude

Jim Macklin wrote:
The barometric altimeter is calibrated to zero at the wheel
contact point with the ground. The GPS measures at the
antenna. Like all things made by man, there are tolerances.

Reason the baro-altimeter is wheel height, think of a 747,
do you want the cockpit or the wheels to clear the trees at
the end of the runway?




Having been on an overloaded business Cessna that took off just clearing
the trees (he raised the gear in ground effect to get a little more
speed to make it) I'd hope that commercial aircraft piloting would be a
little less "bold". :-)

Richard