Negative Relative Altitude Issue with PX4 After Some Flight Time

[Ang]

Hello everyone,

I am experiencing a problem with my PX4 setup where the relative altitude becomes negative after flying for a period.

When reviewing the flight data on Flight Review, I noticed that the GPS Altitude (MSL) turns negative, while the Barometer Altitude remains positive. However, the Fused Altitude Estimation shows negative values.

https://review.px4.io/plot_app?log=6782ebc5-593c-4e24-945b-cd89f8b9d9b2

In some of the flight review records, the Barometer Altitude is showing negative values, whereas the GPS Altitude (MSL) remains positive. Fused Altitude Estimation also appears as negative.

https://review.px4.io/plot_app?log=0a035af0-ed8f-4132-9688-962f3b738c22

Additionally, in the 3D View, the aircraft appears to go underground. Can anyone help me understand what might be causing this issue and how to resolve it?

Thanks for your assistance!

[JulianOes]

Which GPS are you using?

[Ang]

This drone use Here 4(u-blox F9P module).

Here 4 Manual | CubePilot

[JulianOes]

Am I right in assessing that the offsets are only a few meters, right? If so, I’d say that’s somewhat in the normal range.