I know you said you bought another bird but I thought you might like the info anyway.
The following images were taken with my P3P with 1.5.011 firmware:
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GPS Altitude 21.1 m Above Sea Level
GPS Altitude Ref Above Sea Level
GPS Latitude 32 deg 39' 29.62" N
GPS Latitude Ref North
GPS Longitude 86 deg 30' 3.32" W
GPS Longitude Ref West
GPS Position 32 deg 39' 29.62" N, 86 deg 30' 3.32" W
GPS Version ID 2.3.0.0
Lightroom says 69.2 ft. Thats about right since I took off from the side of the freeway that you can see in this image:
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GPS Altitude 1.4 m Below Sea Level
GPS Altitude Ref Below Sea Level
GPS Latitude 30 deg 46' 15.74" N
GPS Latitude Ref North
GPS Longitude 85 deg 56' 51.60" W
GPS Longitude Ref West
GPS Position 30 deg 46' 15.74" N, 85 deg 56' 51.60" W
GPS Version ID 2.3.0.0
Lightroom says -4.6 ft. I can guarantee that the panhandle of florida (Ponce de Leon to be exact) is NOT below sea level. But the -5' is about the difference in height from the shore height plus the height of the picnic table I took off from.
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The confederate flag is north Alabama. Absolutely more than 60' above sea level. Google says Birmingham (which this flag is north of) is 640' AMSL The springs in Ponce de Leon Florida are absolutely not 5' below sea level as google shows the area at roughly 60' AMSL. If your information to me was correct, those figures, especially the one in Alabama should have been in the hundreds of feet.
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This was one of my earliest flights with my P3P. At the time it had 1.1.9.
Lightroom says 15.7 ft which seems right since I took off from the brick platform GD12 is standing on. Milwaukee is about 600' AMSL. So that confirms that 1.1.9 is storing EXIF related to takeoff altitude.
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So based on this data, it appears that 1.5.011 stores relative to takeoff altitude. Whether it uses the barometer or not, I can't say. But it is relative to the takeoff.
And 1.5.011 allows Litchi (and other apps I presume) to use the advanced flight modes. I have used orbit, pano and waypoint missions in Litchi under this firmware which I was not able to do under 1.1.9. It does not have the cold weather battery bug nor the later reduced power "fix" for the batter bug. It also does not seem to gripe about NFZs. The above photo was taken ~2mi from the tower of MKE airport (its not an issue, the area is between any glide paths and there are trees, high tension power lines and a 300' tall water tower within spitting distance). Its doubtful later firmware would allow it to take off.