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Mavic Pro JPG EXIF height firmware fix
876 8 2017-9-8
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isaache
lvl.4
Spain
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Dear DJI representative,

I would like to request a firmware fix to address an issue present in all the latest Mavic Pro firmwares regarding the metadata present in all the JPGs images captured by the drone.
As per the description of the EXIF standard available at http://www.exif.org/Exif2-2.PDF page 47 the GPSAltitudeRef field MUST BE expressed in reference to sea level (ortometric height) however your current firmware embeds ellipsoidal height to the EXIF which is a violation of the EXIF standard.

Thanks for your time and effort.

Isaac
2017-9-8
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Ex Machina
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Flight distance : 1753100 ft
United States
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I'm all for following standards, but is there a way to also report ellipsoidal height in EXIF if GPSAltitudeRef is properly populated in some future update? Perhaps in the MakerNote field?
2017-9-8
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isaache
lvl.4
Spain
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Hi Ex Machina,

Can you please explain why do you need / want the ellipsoidal height? Generally speaking if you have ortometric height you can transform the value to ellipsoidal and viceversa, all what you need to know is which geoid has been used and then compute the undulation for a given position, a good free tool to obtain geoid undulations is https://geographiclib.sourceforge.io/cgi-bin/GeoidEval
Thanks

Isaac
2017-9-8
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Ex Machina
Captain
Flight distance : 1753100 ft
United States
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isaache Posted at 2017-9-8 10:07
Hi Ex Machina,

Can you please explain why do you need / want the ellipsoidal height? Generally speaking if you have ortometric height you can transform the value to ellipsoidal and viceversa, all what you need to know is which geoid has been used and then compute the undulation for a given position, a good free tool to obtain geoid undulations is https://geographiclib.sourceforge.io/cgi-bin/GeoidEval

For casual usage, when I want to know how high I was in a given photo w/o having to look up the height above sea level for that location.
2017-9-8
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isaache
lvl.4
Spain
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Ex Machina Posted at 2017-9-8 10:38
For casual usage, when I want to know how high I was in a given photo w/o having to look up the height above sea level for that location.

Hi Ex Machina,

I'm sorry I believe I don't quite understand your explanation, can you please provide an example of such an application?

Thanks

Isaac
2017-9-8
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Ex Machina
Captain
Flight distance : 1753100 ft
United States
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isaache Posted at 2017-9-8 11:31
Hi Ex Machina,

I'm sorry I believe I don't quite understand your explanation, can you please provide an example of such an application?

Sorry, I had some mistaken assumptions about the spec and DJI's implementation.

Along the way to understanding I discovered an inconsistency in altitude recorded between DNG and JPG versions of the same photo when shooting RAW+JPG.

kMDItemAltitude: DNG              = 34.6
kMDItemAltitude: JPG                = 478.222



2017-9-8
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isaache
lvl.4
Spain
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Ex Machina Posted at 2017-9-8 12:43
Sorry, I had some mistaken assumptions about the spec and DJI's implementation.

Along the way to understanding I discovered an inconsistency in altitude recorded between DNG and JPG versions of the same photo when shooting RAW+JPG.

Hi Ex Machina,

No worries, what you see on the DNG is the altitude over the take off point whereas the JPG is reporting the height over the ellipsoid, for the average Joe the ellipsoid means nothing, it just happens to be one of the reference surfaces internally used by the GPS receivers (like the one on the Mavic) to compute the the position altitude although nowadays most GPS receivers include Geoids to transform that height to sea level.

Isaac
2017-9-8
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Ex Machina
Captain
Flight distance : 1753100 ft
United States
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isaache Posted at 2017-9-8 13:06
Hi Ex Machina,

No worries, what you see on the DNG is the altitude over the take off point whereas the JPG is reporting the height over the ellipsoid, for the average Joe the ellipsoid means nothing, it just happens to be one of the reference surfaces internally used by the GPS receivers (like the one on the Mavic) to compute the the position altitude although nowadays most GPS receivers include Geoids to transform that height to sea level.

Thanks, Isaac, I'll try to read more closely next time. ;)
2017-9-8
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isaache
lvl.4
Spain
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Hi,

Nevermind my request I have discovered that the altitude inserted in the JPG EXIF tag may be wrong by hundreds of meters (in clear view of the sky) when comparing flights made on different days there is no way to know if the heights is ellipsoidal or ortometric.

Isaac
2017-9-11
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