Baro altitude uses GPS?

I have a pixracer with plane 4.1 Anybody have any idea why the altitude on my GCS [ or taranis telemetry ] changes the second I get a GPS lock when I have the source for altitude set to Baro?? Also what source would be recommended for a longer ‘auto’ flight? GPS or baro? thx

The barometer drifts (I think as temperature changes). The longer the flight, the more it drifts.

True. But I’m referring to it will read 0 meters but after a minute or so it grabs 4 sats it instantly jumps to say 3 meters or so. I don’t understand why the gps has anything to do with it if I have my Alt source set to baro.

Try this, let it get a full EKF fix and then arm the plane. See if altitude resets to 0 when you arm it.


The Baro altitude is a relative measurement. It is relative to the home point and set to zero while arming the plane.

My plane auto arms. It’s armed as soon as it’s booted. I don’t have rudder arming on. It changes when it gets a 3d sat count.

I might have to do that… rudder arming??

Rudder arming or switch arming. Both do the same.

What aslo might happen is that if for some reason in the GCS you have set the altitude to ASL instead of AGL which measures the baro altitude and then adds to that value the GPS elevation. I’m not sure if that’s the case, but it’s certainly a possibility!

You can check the logs and see the values RelAlt and Alt in the GPS category.
RelAlt is from the barometer and Alt is barometer + elevation I think

AGL: Above Ground Level
ASL: Above Sea Level

Thanks… It’s set to AGL but that was worth checking. I guess the best solution is do rudder arming. I simply won’t arm it until I have a decent sat count.

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Yeah, try that! Maybe it gets confused on boot or something, because it arms before GPS lock, and that’s not a good idea mostly.

I turned on rudder arming… MUCH better!!


May I request that 4.1 build should includeimage parapeter just like copter.

I am working with Civil Aviation, and one of their requirement for Altimeter is “Programmable based on altimeter setting (in-Hg)”.

I have noticed a big deviation in altitude when flying a plane. Not accurate at all, sometimes off by 200ft.
Since Civil Aviation must work with manned aircraft, they want all UAS to report the correct altitude. I am guessing +/-50 feet deviation is ok.

Thanks for adding this request to the next build.

I just had the same exact same thing happen… Altitude would say zero and the second got a GPS lock it would jump to 80 ft or so… Found out it was because I had q ground control connected through mavlink and had update homepoint based on device location enabled… Android tablet crappy GPS was messing things up I guess.

Unchecked that and altitude is zero before after enduring take off now like it’s supposed to be… just in case someone has this problem in the future.