Altitude shown in Fly app

[David Axworthy]

I've noticed my Mavic 3 doesn't show accurate altitudes, much of the time. It is often 10 ft to 20 ft off the true altitude, based on comparing my height above the ground to known altitudes of object around my property, like certain tries, to top of my chimney, my windmill, things like that. I've seen it hover above the ground about 2 ft and the altitude shows it at 20 ft. I thought the vertical gps accuracy was only a couple of feet, and I've never had this issue with my Air 2. Any ideas on what is causing this, or any way to mitigate or correct? I'm worried about running Waypoints if the drone doesn't know it's actual altitude.

 

[Meta4]

First ... just to be sure that we are on the same page
The height shown on your screen is the height relative to the launch point.
I's not the height above whatever is below the drone.

I thought the vertical gps accuracy was only a couple of feet

Your drone does not use GPS for altitude.
It uses a barometric sensor which measures small changes in air pressure - just like the altimeter in a real plane.

and I've never had this issue with my Air 2. Any ideas on what is causing this, or any way to mitigate or correct?

If you are talking about a 10-20 ft difference between the indicated height between the start of a flight and when you bring the drone back, that's common and normal due to changes in air pressure over the duration of a flight.
... and this would also happen with your Air 2.

I'm worried about running Waypoints if the drone doesn't know it's actual altitude.

Your drone does not know its height above the ground (except when within the limited range of teh VPS sensors).
Just like a real plane pilot, you need to understand that the barometric sensor could be 10-20 ft out during a flight and position any waypoints accordingly.

 

[1911tex]

In an airplane, the altimeter is based on the barometric pressure like your UAS signal....that is why when receiving landing instructions, the tower will give a current barometric pressure at the landing airport.....especially important if you are flying IFR; those 20 feet on landing may be very important!...the BP will most likely be different than the departing airport or enroute readings....and may be dramatically different!!!