[Paparazzi-devel] measuring altitude with pressure/gps

[Martin Mueller]

Hi,

we are looking into meteo data that we collected using Parrot Bebop2 and were 
wondering if there is an altitude parameter which is already kalman filtered 
based on GPS and pressure measurements. So far we have been relying on the 
ROTORCRAFT_FP:up parameter and applied a linear detrending routine to bring the 
start and landing altitude to 0m (accounting to pressure changes).

However we just realized that the difference between the GPS and the other 
parameters is generally increasing with height so we wonder a bit whether the 
other parameters are purely pressure based and there is a problem with the 
hydrostatic equation. Maybe the assumed temperature profile doesn't fit the 
conditions we were facing (much colder), but we are not sure how much of an 
error to expect from this.

We are generally wondering if there is one parameter that is already kalman 
filtered. It doesn't look like it since ROTORCRAFT_FP and INS are almost 
identical (except for the sign convention and sampling rate) and look very 
similar to the AIR_DATA:amsl_baro (seems to be pressure based). None of them 
has features like the jumps one can see in the GPS data.

Can we use the paparazzi Kalman filter to easily postprocess a "fused" altitude 
from GPS and pressure?

Martin