I regularly take photos for developers requiring per level photos.

DJI Go / Inspire & Phantoms now just record EXIF Altitude as Above Sea Level.
A few FW versions ago JPG would be Altitude above sea level and DNG would be AGL

I am at a client site today just meters away from the Pacific Ocean and estimated no more then 15m above the water level. I was taking low level photos that specifically need to be at certain levels. I establish a base height "AGL"  that relates to the floor level (as you can't see the DJI altitude sea level anywhere in the app etc). Take my shots, rise the required floor rise height and repeat.

Get back to the office and the Sea Level Altitude values aren't consistent in the EXIF data.

I took on the ground photos (taken to set a base reference) my DNG photos show as -99m, I then fly it up 100m AGL (from my take off point). Take some photos and now they say 1m.
Remember my take off point is only about 15m above the water level. .

I use an iPad Air 2 with 4g

I miss the ease of height information that was captured 2 ways in previous FW versions.

Altitude is Above Sea Level
Elevation is height from terrain surface to Sea Level
AGL (above ground level) is how far you will fall to the Ground below

AGL out of all is the constant and more easily related to a site I feel.

How do others deal with the Altitude values? I figure that values will change with Barometric pressure. As we know that's never a constant value.

It was just suggested to me that the heights being recorded may actually be GPS altitude. Makes sense as sometimes there may be interferance for structures.

Still hard to work with though.

DJI responded some time ago about the JPG / DNG values and advised they would be fixed. At the time they said ASL.

Last I check it hasn't been fixed.  Last flight 20 days ago.