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I have spend a bit of effort trying to figure out what the geographic projection is of coordinates attached to the exif files of the photos taken on the DJI Phantom 3 advance. I assumed that it was in WGS84 with the elevation in its associated datum, but when I looked closely at the elevation values, there was a systematic offset that was closer to the NAVD88 datum (but still off).

I called DJI's tech support and was put on hold for a while, and they reported back that the it was indeed NAVD88. I am not sure I buy this answer though. The person I was talking to had no idea at first, and I had planted the term navd88 when I posed the question, and even spelled it out for him; I asked if the z was in a global ellipsoid or a local datum like navd88.

Like I said, I was on hold for a long time, so it is possible this is really the correct answer, but when I think about it, it doesn't make sense. These are flown all over the world, so why would you want a North American datum if you are flying in Tasmania for example. I suppose it is possible there is a list of local datums onboard, and it automatically applies it depending on the location, but I kind of doubt it.

I know that the onboard GPS in not very accurate, especially in the Z direction, but where I am at there is more than 13 meters difference between the WGS84 global ellipsoid and NAVD88. Knowing the datum will help strengthen my photogrammetry product.

I also went through all the DJI documentation I could find on the subject, to no avail.

Has anyone else examined this issue in detail?

Thanks!

user8934934
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  • 13m is less than your device GPS elevation accuracy. Whata re you trying to get anyway? – Amir Nov 17 '17 at 04:48

2 Answers2

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I was thinking the exact same thing! Which datum is used, so propably WGS84. But yes if you are in Tasmania, that make a difference, you can have more than hundred feet diffence if you are looking at a specific waypoint. But at the end, that makes no diffence of using the "universal datum" WGS84, because when you use a point as a "RTH" point, you not entering a geodesic point (lat/long). But the drone is recording where is at according to what it's reading! The day that DJI will offer to enter a coordinated, then, exact country datum will be required.

Another "BUT".... if you are looking at your flight records, while playback your flight, at the bottom you can see you coordinates, so if you have an nicking gps, and that gps is set at WGS84 datum, do that exercise, enter you coordinated on google earth and check where it's landing. Then change gps datum to another datum, nad27 or what ever and enter again your coordinates and check again, you will be surprise of the distance difference!!

Take care!

Ben
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based on my experience, Phantom 4 is using the WGS84 as datum. I made experiment by taking several GPS reading at 1 site used for GPS calibration. The reading from all GPS is slightly matching the coordinate of calibration point.

Then I take a reading via phantom 4 and its not matching with the calibration point. I changed the datum from the Phantom 4 reading into Timbalai 1948 (datum use in Borneo Island), the coordinate is matching with the calibration point.

Therefore I confident that datum used by the Phantom 4 is using WGS 84 since this datum is universal datum and also used by Google Earth.

haidar ali
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