Incorrect height readout

[Bcornell11]

First time this has happened but I noticed that they height readout was pretty off. I was hovering about 2 feet off the ground and the high read -17 ft anyone have any ideas what might have caused this? The proceeding flights were fine..

 

[The Editor]

First time this has happened but I noticed that they height readout was pretty off. I was hovering about 2 feet off the ground and the high read -17 ft anyone have any ideas what might have caused this? The proceeding flights were fine..

Yes - barometric fluctuations.
Although the barometer in the Mavic (and other DJI platforms) has a resolution of around 10cm it will never give an accurate and reliable reading of agl.
And GPS certainly won't!
Take it as a guide only, you will often see negative values when you have been flying around for a few minutes and then bring the aircraft in close to the deck.
Gusty conditions can affect the barometer and at other times it will be quite accurate - just don't rely on it.

 

[Bcornell11]

Thanks for the explanation glad it's nothing to be concerned with.

 

[kmaluo]

Yes - barometric fluctuations.
Although the barometer in the Mavic (and other DJI platforms) has a resolution of around 10cm it will never give an accurate and reliable reading of agl.
And GPS certainly won't!
Take it as a guide only, you will often see negative values when you have been flying around for a few minutes and then bring the aircraft in close to the deck.
Gusty conditions can affect the barometer and at other times it will be quite accurate - just don't rely on it.

Is the GPS sensors not accurate enough for height?

 

[The Editor]

Is the GPS sensors not accurate enough for height?

No, GPS (on any device) other than military spec is woefully inaccurate with altitude.
It can be 400ft out depending on the HDOP/VDOP at the time.
It is basically to do with the timing differences and the mathematical model of the Earth's shape (which has errors).

 

[Raptorman]

Yeah, the baro will drift but generally take time to accumulate much of a difference hence it's used to help control altitude. Closer to the gound you have sensors looking down that are, or can be, much more accurate. GPS, as E stated, is quite limited in altitide accuracy though 400 feet is probably at the very limit of possibe error with 40 feet being much more likely. One of the things that effect GPS altitude accuracy is the way the samples are averaged tending towards a lagging value.


Brian