To add some more information to this discussion.

Here is metadata from an image from the above workflow taken from a

Phantom 4 Pro V2.

This flight was conducted at a commanded 180 feet (54.86m) relative altitude.

Absolute Altitude: 31.53m

GPS Altitude: 31.5m

Relative Altitude: 56.2m

The height above ellipsoid (Assuming it is WGS84 ellipsoid since the metadata of the map is not saying if it is WGS84 or GRS 80) for the coordinates of the image is -33.54m. This is from an Arc Online Ellipsoid layered map.

The orthometric elevation of this point using the EGM96 gravity model/geoid is 2m which matches up well when using NAD83(2011) and hybrid Geoid 18 (Most current geoid before the new horizontal and vertical datums are released very soon). Using Hybrid Geoid 18 I get around 1.8m for my orthometric elevation.

So lets try to figure out if the absolute Altitude reported by the drone is above the orthometric height. 54.86m as commanded from the planning software or 56.2m from the Relative Altitude above either the WGS84/EGM96 height (2m) or the NAD 83 (2011) Geoid 18 height of 1.8m would be totally incorrect with these heights adding to the originals. So unless I am missing something, Absolute Altitude is not being reported as above an orthometric height.

Next let's see if this is an above ellipsoid height.

The ellipsoid height for the coordinates from this image as reported by the ellipsoid map I use from Arc Online has an elevation of -33.54m. If I take the Relative Altitude of 56.2m from the metadata and get the difference from the ellipsoid height I get 22.66 meters above the ellipsoid. If I even take the commanded from flight planning software height of 54.86m and do the same I get 21.32m above the ellipsoid. Neither of these match up well with our 31.53m, but they do match better than our above orthometric height value of around 58m.

Just guessing I would guess that 31.53 is reporting as above ellipsoid and is just very inaccurate.

A final piece of the puzzle was thrown at me while playing around with our new Matrice 300RTK and using the cool and free for now Beta of DJI Flight Hub 2.

For the same area (I eyeballed it) DJI is saying that the orthometric height is 7.6m??? and the ellipsoid height is -27.9m????. I know this area pretty well and, no the orthometric height is not 7 meters. This could be a misprint as 7.6 feet would be close to being true with it converting to 2.3 meters. Next their ellipsoid elevation does not match the Arc Online ellipsoid map (assumed to be WGS 84).

Lets now use DJI sourced ellipsoid information (The only DJI info I ever found) with our metadata.

Take the difference between the ellipsoid height from what DJI Flight Hub 2 says it is at -27.9m and apply of image's Relative Altitude of 56.2m and we get 28.3 meters above the ellipsoid for our image. This is much closer to the Absolute Altitude of 31.53m but still no cigar.

What is the point of all of this? Nothing but to get a discussion going and for me personally to see if I am missing something in my thoughts on the vexing DJI elevations.

If you see my thinking is off or have something to add please do so.