Accuracy of Altitude in EXIF Data

[PapaBob]

I mainly shoot still images from my M2P in DNG format and have never paid much attention to the GPS EXIF data. I was reviewing an image today and had a metadata window open which showed the flight altitude at 291m or 955'. This made my heart skip a beat since I keep all my flights under the 400’ AGL limit of section 107 and set the controller altitude limit to 120m (my flight was in class G airspace). I then remembered that I had taken this shot in Wisconsin (I live near sea level in Florida) and determined that the launch point was at 181m MSL; so the bird was at about 110m or 361’ AGL which was in the ballpark for this shot.

I believe the altitude read out on my Smart Controller is from barometric readings by the M2P which determines altitude above (or below) launch point. I assume the altitude in the picture EXIF data must be GPS as is the Lat and Lon. I am curious if anyone has found information that compares the accuracy of the GPS altitude reading (adjusted for MSL of launch point) and the altitude reading from the M2P altimeter. I am also curious as to the margin of error in the altitude reading (MSL) imbedded in the EXIF data in my photographs.

Any corrections to my assumptions or comments are welcome. I am still foggy on the difference between Geoid and MSL. Thanks in advance for your time.

 

[Meta4]

I assume the altitude in the picture EXIF data must be GPS as is the Lat and Lon. I am curious if anyone has found information that compares the accuracy of the GPS altitude reading (adjusted for MSL of launch point) and the altitude reading from the M2P altimeter. I am also curious as to the margin of error in the altitude reading (MSL) imbedded in the EXIF data in my photographs.

If you dig into the image metadata, you'll find two different altitude fields, one shows the relative altitude that you see on the screen and the other shows the absolute altitude, which is what you've found.
In the Mavic 2 it comes from GPS.
In older DJI drones it comes from a flawed interpolation of barometer data assuming standard pressure details and can have an error (because atmospheric pressure varies) of a couple of hundred feet.
Like this:

I'm not aware of whether anyone has determined the source of the data for Mavics since the Mavic 2.

Just to confuse people further, DJI labels the Absolute Altitude as GPS Altitude even though it came from barometric data.
They later changed the data for the Mavic 2 to come from GPS data.
This confused anyone trying to solve the mystery of DJI metadata altitudes.

I am still foggy on the difference between Geoid and MSL.

MSL relates to where the sea really is.
The geoid is a mathematical approximation for the shape of the earth.
But the earth's shape is too complex to be accurately represented by a simple mathematical formula.

 

[sar104]

I mainly shoot still images from my M2P in DNG format and have never paid much attention to the GPS EXIF data. I was reviewing an image today and had a metadata window open which showed the flight altitude at 291m or 955'. This made my heart skip a beat since I keep all my flights under the 400’ AGL limit of section 107 and set the controller altitude limit to 120m (my flight was in class G airspace). I then remembered that I had taken this shot in Wisconsin (I live near sea level in Florida) and determined that the launch point was at 181m MSL; so the bird was at about 110m or 361’ AGL which was in the ballpark for this shot.

I believe the altitude read out on my Smart Controller is from barometric readings by the M2P which determines altitude above (or below) launch point. I assume the altitude in the picture EXIF data must be GPS as is the Lat and Lon. I am curious if anyone has found information that compares the accuracy of the GPS altitude reading (adjusted for MSL of launch point) and the altitude reading from the M2P altimeter. I am also curious as to the margin of error in the altitude reading (MSL) imbedded in the EXIF data in my photographs.

Any corrections to my assumptions or comments are welcome. I am still foggy on the difference between Geoid and MSL. Thanks in advance for your time.

Firmware v01.00.0510 EXIF altitude changes

A number of people have noted that the latest firmware has changed the EXIF altitude data, but DJI did not specify exactly what had changed. I guessed that it was what I had been bugging them about – namely that the altitude data fields were mis-labeled, e.g. : GPS Altitude Ref ...

mavicpilots.com

 

[EagleHead]

My M3 exif indicates they use WHS-84 map datum.

 

[Meta4]

My M3 exif indicates they use WHS-84 map datum.

That would be WGS-84 .. the common default datum worldwide.

 

[EagleHead]

That would be WGS-84 .. the common default datum worldwide.

Thank you for this correction. My fat fingers...