mavic pro negative altitude on landing

[niki]

Deviation is between -1 to -6.8 feet, not meters. Mainly am hoping I would not get unexpected water landings.

Where did you saw I'm talking in meters?
Why you think the drone will land unexpectedly in water, did it had unexpected landings so far?

 

[MavicCF]

I think if Mavics were landing negative every time, there would probably be hundreds of posts rather than just a handful that I've found. I looked at the airdata on my older mavic and I saw a couple negative landings out of dozens of flights, but it wasn't *almost every time* and that is why I think it is an anomaly. I was trying to gauge the seriousness of the situation by posting here. I'm not happy about trying to do an exchange as this was a refurb and I could get another Mavic that has a more serious problem. It's also a hassle. It's a dice roll, hence the discounted price. It could be the reason it was sent in before and DJI QC didn't catch it or didn't care, who knows.

I wouldn't mind posting a DAT. I'm assuming you grab this from DJI Assistant? If you can point me to a quick guide and place to post it, I can do that tomorrow morning.

Here's instructions on getting an AC DAT. Usually you have to upload it to Dropbox or similar cloud storage and post a link to it here.

 

[whitekat]

My mavic kept showing -4 alt. No problems. I was flying by a tower and got bad interference. When I landed the alt was at 189 ft. I took it for a second flight and when I landed the problem was fixed

 

[jwblair]

Aloha!
This sounds like "normal" drone altitude error. We wanted to use drones to catalogue sea life here in Kaneohe Bay. If you know the size of an object (in pixels) and the altitude that the picture was taken, you can calculate the actual size of the object (if you have calibrated your camera using an object of known size). We found out we couldn't do this due to the errors in the drone's displayed altitude.

In my calibration tests I discovered that the displayed altitude during a flight could have an error of up to 8 feet and that the GPS altitude stored in the picture's metadata was totally useless. This has nothing to do with changing barometric pressure, which was constant during the tests. We observed displayed altitude errors in both the Mavic Pro and Phantom 4.

I've attached my calibration data below.
John