DJI Geotagging issues

Hi David ! I am having problems with the Phantom 4 pro with the geotagging of altitudes. I changed for faster SD SanDisk Extreme and Sandisk Extreme Pro and I still have the GCP above the images, always in ellipsoidal height. I have seen in other forums you have made a comment about it that I cannot resolve. Cheers

Hello Луис,

Send me a PM and I’ll see if I can help.

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You already tagged the GCP’s?

I don’t understand Chas! I have the GCPs georeferenced, but it gives me an error in the ellipsoidal height. The GCPs are higher than the ellipsoidal heights of the cameras.
P4P not RTK

What processing software?

Hello! At the moment I am not using software, I only compare the ellipsoidal height of the GCPs and the geotagging of the photos.
When comparing the flight height in absolute values, it is lower than that of the GCP. I’m going to try to calibrate the compass, I can’t think of anything else since with the Parrot Anafi I don’t have these differences.

Luis, you must understand that the elevation reported on P4P images (exif) has nothing to do with elipsoid. It is simply the elevation above the point at which you take off.

If you have recorded your GCPs using elipsoid, and you want your P4P images to also reference elipsoid, you will have to adjust the elevation in all the images by taking the elipsoid height of the take off point, and adding the height at which the mission was flown.

Example. If the surface where you took off is 70 meters (elipsoid) and you flew the mission at 50 meters, you will need to add the 70 meter (surface height) to the elevation of the images.

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Dave, yes I understand but this didn’t happen before. Why is the ellipsoidal height different from the one indicated by the GPS in relation to the geotag? If I take a photo on the ground and compare it with the flight elevations, it gives me the difference of the flight 60 meters. What I don’t understand is why the photos are geotagged in another elevation reference system and not in WGS84. ?
Parrot anafi geotag ellipsoidal height a in wgs84

It is because the geotag does not reference elipsoid. On the P4P, the “GPS Altitude” tag is not really referencing GPS altitude at all. The P4P is using the barometric sensor to define an altitude. And then as the the drone lifts off, it assigns a “relative altitude” again by using the barometric sensor. The P4P is not using GPS assigned altitudes.

The P4RTK and the Evo2 RTK use elipsoid but not the P4P. None of the altitude tags on the P4P images relate to elipsoid, geoid, or orthometric heights.
The P4P was not intended to be a mapping drone by design.

I have no experience with the Anafi.

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Ahhhh OK !! now I can understand. So I’m going to have to make these corrections to the EXIF ​​file or buy an RTK module.
Thanks for your help
Luis

If you process in Metashape, you can add all of your images and then change their altitude very easily. Collect a point with your Emlid receiver at the take off location. Then, you just add the relative altitude (mission flight height) to the elevation of the point you collected and adjust all of the images to that correct height (within some meters) in Metashape.

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