Negative relative alitude at launch

Hi there,

I've been slowly building and tuning my first quad and have noticed a small anomaly I can't figure out.

For some reason, my GPS' relative altitude is showing a negative value both before takeoff and after landing. The value is not consistent across flights nor is the value the same before takeoff and after landing.

I've attached a few graphs which show relalt on the left axis and HDOP/NSATS on the right.(Cross posted from Ardupilot forum as the audience here is far larger)

The baroalt tracks almost identically with the relalt tracks shown above.

I can appreciate that if I had poor GPS coverage that the 3D position may be out a little (even if I think the HDOP is probably acceptable) but it doesn't explain why the position starts in negative territory.

Can you suggest a cause or method of further investigation?

Many thanks.

relalt1.jpg

relalt2.jpg

relalt3.jpg

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Replies

  • Hi all,

    Does anyone have any thoughts on how to debug this?

    Many thanks.

This reply was deleted.

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