[Paparazzi-devel] VFF_FLOAT - question about the Kalman filter

[Michal Podhradsky]

Hello guys,

I am currently adjusting the VFF filter (z_dd, z_d, z estimation) to our rotorcraft airframe (i.e. changing the process and measurement noise covariance). As the filter is currently implemented, in the propagate phase (vff_propagate) the measured acceleration is propagated to all three states with zero noise (line https://github.com/paparazzi/paparazzi/blob/v4.0/sw/airborne/subsystems/ins/vf_float.c#L86). Is there an assumption that the IMU accelerometer is always correct?

If I understand it correctly, the barometer (z measurement) and accelerometer(z_dd measurement), and optionally other sensors (sonar etc.) should be updated at different frequencies. In the current master branch ( https://github.com/paparazzi/paparazzi/blob/master/sw/airborne/subsystems/ins/vf_extended_float.c ) are already separate updates for baro (offset) and gps/sonar/etc (no offset) sensors, but the acceleration is still propagated directly. 

Do you know why the filter was implemented in such a way?

Thanks a lot!
Michal