Drone drops in altitude, ZED-F9P

I’m using the Holybro H-RTK F9P, HGT_MODE is set to GPS. During hover the drone descends on its own after a couple of minutes, ranging from ~3 -10 m. The error has been encountered multiple times with different drones, but it seems to happen more often if the temperature is around 0 degrees Celsius.
When the fault occurs the GPS height is more or less constant and one thing in common between the fault instances is that the epv decreases during the fault. However the epv is quite low to begin with, starts at ~0.5 and decreases to 0.3-0.2.

Px4 version: v1.12.3
ublox GPS version: 1.30

I’ve also tested with the newest ublox version (1.32) but that resulted in a small fly-away.

Has anyone had similar issues? Is there a certain ublox gps version that is reliable?

This sort of stuff is so much easier to troubleshoot with Logs.

You say that the EKF2 isn’t showing the quad increasing in height when you start going up…this is where I would start. Why isn’t it increasing height? What other data is it using to come up with this estimate?

Even though GPS is set as primary…it’s possible the other sources are goofing it up.

Also- have you tried the latest version of PX4? Build master and try again.

Thanks for the reply!
The problem seems to be more that the raw gps value is not updating as it should. When the fault occurs the drone starts to descend and the gps value is basically the same. There can be as much as 10 m difference.




The barometer values in these logs reflects the height of the drone observed by the pilot.