Hello,

I am using the D-RTK2 with the Mavic 3E.

RTK Base station is reporting a Geoid12b elevation of -33.xxx meters
My Photos are being tagged with a lat/long/elev of lat/long/29.xxx meters

This places my drone about 60m above Geoid and my flight was around 150 ft AGL

I have control points set using State Plane feet elevations.

What's the beset practice to get a point cloud from Terra in ortho meters on the ground?

Do I make adjustments to the RTK location on the controller (I'm not sure of the difference between my GEod12b elev and NAVD88), or do I let it fly and use some conversion later? Also, if I use the GCP's elevations (converting feet to m) I am around 20m ortho. How would I unput these as GCP's in Terra?

Hi,
In DJI Terra you have to import the geoid model. It must be in a very specific format available on this site: https://cdn.proj.org/ It is obviously not available for all countries.
Then you should be able to select the geoid to perform the correction automatically.

Personally I use Agisoft Metashape, I can use the geoid made available by the national geographic agency, and for the management of GCPs I find the software much simpler. There are other PIX4D, WEBODM... it's up to you to find what suits you best.

Type "geoid" in the search bar of the forum, you will find a handful of threads of the same subject with very complete answers. This problem is not specific to the M3E, all images' altitude from DJI drones are in ellipsoidal format.

THIS PART IS KEY:

"altitude from DJI drones are in ellipsoidal format."

adjust to your preferred vertical datum

So, what I've figured out so far:

RTK is recording in lat/long/meters based on geoid12b

I import photos to Terra and run AT using WGS84 horizontal and default vertical datums.

After AT is done, I add GCP file and set to datum to my NAD83 state plane and NAVD88 - Pick targets from all photos and then Optimize

Build 2D and 3D models with same output datums (State plane and NAVD88)

Does that sound correct?

Thanks,
Mike

djiuser_UnnxQBILqKKA Posted at 11-25 18:28
So, what I've figured out so far:

RTK is recording in lat/long/meters based on geoid12b

-The altitude provided by the drone refers to the green line, which is an ideal model of the curvature of the earth.
-The altitude which refers to the geoid, to the red line, reflects the real curvature of the earth.

-The difference between the two is the geoid height "N"

For a 2D model, it doesn't matter, makes everything ellipsoidal, skip the geoid transformation step.

I never got used to Terra. I use Metashape, it's much more complete and easy to use to control the quality of vertical alignments, from my experience.