What's The Consensus on EXIF Elevation Data Craziness?

[Consultant]

So after flying many missions with a P4A I recently wanted to verify the elevations I thought I was at for some photos is correct. Photos were taken with DroneDeploy and some with Lichti (for panos.) When I upload the nadirs to DD, it correclty states the resolution is 0.9 in/pixel which is what I set the mission at which is around 230ft AGL elevation for the P4A/P4P camera. However the EXIF elevation for all the photos is 42. I thought that must be meters but 42x3 = 126ft still way too low. So I know for sure the EXIF elevation is a bunch of BS. I've seen discussions about barametric, GPS, bla bla bla and I could never find any sort of summary conclusion as to what is DJI storing and how is it being calculated.

More importantly is there software I can use to see the "real" elevation, like in the XMP data? Which software (Windows). Essentially, tell me how I can verify what elevation AGL I flew at, looking at the photo data, not the mission data!

 

[GMack]

I've never trusted the DJI reported altitude. I can take off at Home Point saying Zero Feet, and come back to land on same spot and it is -46 feet. Autopilot has a slider to set the accuracy and I think its default was 46 feet (Same as DJI ??), but tightest was only 16 feet so not much of an improvement with my P4 Std. It's a toy and not some military grade aircraft or Trimble mapping drone so I don't expect much out of it.

 

[Meta4]

So after flying many missions with a P4A I recently wanted to verify the elevations I thought I was at for some photos is correct. Photos were taken with DroneDeploy and some with Lichti (for panos.) When I upload the nadirs to DD, it correclty states the resolution is 0.9 in/pixel which is what I set the mission at which is around 230ft AGL elevation for the P4A/P4P camera. However the EXIF elevation for all the photos is 42. I thought that must be meters but 42x3 = 126ft still way too low. So I know for sure the EXIF elevation is a bunch of BS. I've seen discussions about barametric, GPS, bla bla bla and I could never find any sort of summary conclusion as to what is DJI storing and how is it being calculated.

More importantly is there software I can use to see the "real" elevation, like in the XMP data? Which software (Windows). Essentially, tell me how I can verify what elevation AGL I flew at, looking at the photo data, not the mission data!

A long time ago, DJI used the barometer data for the Exif altitude info but about two years ago they changed that to use GPS altitude data.

This photo taken up in the hills shows an altitude of 470 metres, which is about right for that area + the height I flew at:

Another image shot much closer to sea level:

The GPS altitude shown is -18 metres which shows why DJI do not use GPS for altitude data.
GPS is good for horizontal positioning but very inaccurate for altitude.

The photogrammetry programs seem to work things out properly despite the dodgy GPS altitude data.
Perhaps they use the barometer data which I have been told is still hidden in XMP data somewhere.

 

[Meta4]

I've never trusted the DJI reported altitude. I can take off at Home Point saying Zero Feet, and come back to land on same spot and it is -46 feet. Autopilot has a slider to set the accuracy and I think its default was 46 feet (Same as DJI ??), but tightest was only 16 feet so not much of an improvement with my P4 Std. It's a toy and not some military grade aircraft or Trimble mapping drone so I don't expect much out of it.

What you describe is not related to the altitude info shown in Exif data.
You are describing a Phantom that needs to have an IMU recalibration because its barometric sensor is showing significant inaccuracy.
A change of a few feet over the time of a flight can be normal but 46 feet is too much and could be a flight safety issue.
If an IMU recalibration doesn't improve it, I'd be asking for a repair or replacement.