[Paparazzi-devel] RE: distance measurement for landing. (Chris)

[Chris]

I think that i good, simple and feasible idea (someone i think mentioned 
it) would be to use two barometers, calibrated together of course, and 
have the ground station automatically transmitting a correction for the 
airborne altimeter (effectively change the ground altitude or pressure 
variable ).
With a precision barometer we can then set the ground pressure the same 
for both the ground station and the airplane thus allowing precise 
altitude measurement.
Since the precise altitude of the take off point will be known from SRTM 
or from an accurate gps and cannot change unless there is a big 
earthquake or a volcano erruption :-) the plane will always have an 
accurate barometric altitude for short missions.
AFAIK real pilots do the same by getting the ground pressure from the tower.
Chris