GPS & baro fusion problem

[matejbone]

Hi!

I have a question regarding EKF2 fusion.

PX4 is set up to use GPS as a primary source for EKF2_HGT_MODE.
Reported altitude is OK until the GPS receiver is jammed. In that case, fusion creates a problem, because it merges invalid position from GPS and baro and from that point on fused altitude is incorrect. Px4 thinks it's flying way higher than it actually is.

Is there a way in the parameters to set up in case of invalid GPS to use baro as a primary source. Could I set PX4 to turn off fusion when GPS signal is invalid? I think that is feeding info in the Kalman filter even when it's invalid and from that point on fused altitude does not return to GPS reported one.
Flight1

Flight2
I tried using EKF2_GPS_V_GATE and EKF2_GPS_P_GATE more restrictively but without any luck.

Thanks!

[julianoes]

Good question. Let me ping @bresch and @CarlOlsson hoping that they have answers.

[CarlOlsson]

Unfortunately I don't have experience with GPS as primary height source. @matejbone Just curious, why don't you want to use baro as primary height source?

[matejbone]

I tried to use GPS, because after a long flight 2+ hours I had in mind that barometric pressure would change and that would affect the approaching height.

How do I adjust weight between both? Is there a parameter?

[CarlOlsson]

How do I adjust weight between both? Is there a parameter?

No the EKF only uses one of them at the time. Here is some super old issue regarding baro offset estimation PX4/PX4-ECL#44

[julianoes]

FYI @RomanBapst @jkflying

[jkflying]

Use baro as primary height source. The offset will be re-estimated using GPS if available, so you shouldn't have drift.

There were some ideas from @kamilritz about doing multiple height source fusion (vision, lidar, baro & GPS all together) but this would require a big rework of the EKF.

[matejbone]

OK thanks for the help to all!

I will try to use baro and see what happens if GPS is jammed.

[RomanBapst]

Use baro as primary height source. The offset will be re-estimated using GPS if available, so you shouldn't have drift.

@jkflying Can you remind me where we are doing this? I was under the impression that we don't compensate for baro drift.

[jkflying]

Hmm, it seems we only do that if we don't use baro as primary.

https://github.com/PX4/ecl/blob/81c6d6655f6e409cac549ed8537b22996b413028/EKF/control.cpp#L1083-L1092