Hello everybody,

I'm using a DJI Mavic 3E with RTK to create 3D  models with DJI Terra. I'm having problems when I transform the  coordinates and heights when creating the model with DJI Terra.

Since  all the DJI Terra updates from version 3.4.4, I'm not able to get the  right heigth in the model (LN02). The output model has an 50m offset  (more or less).

I'm wondering what has changed since DJI Terra  version 3.4.4 as I'm using he same options and same drone and since  then, I have to recreate the model adding a correction offset to get the  right heights.

I'm using the following output options:

• Output Coordinate System: WGS84 + Default -> Getting an offset 50m in the output
• Output Coordinate System: WGS84 + LN02 -> Getting an offset 50m in the output
• Output Coordinate System: CH1903+ / LV95 + Default -> Getting an offset 50m in the output
• Output Coordinate System: CH1903+ / LV95 + LN02 -> Getting an offset 50m in the output
  

So basically, the geoid setting is doing nothing.

I  don't know if I'm doing something wrong or if there is a problem with  DJI Terra (actually using 4.0.8). I Will appreciate any advice or  solution.

Thanks a lot!

Version Number: 4.0.10 seems to have addressed this issue.

From release notes:

Ÿ Fixed the issue of ineffectiveness in modifying the base station center point data in the
LiDAR Point Cloud Mission on Terra v4.0.8.

Thank you! I will check right now

Swiss_Drone_3D Posted at 4-11 22:28
Thank you! I will check right now

You risk being disappointed because the reference of the base station has no relation to the geoid.

I belive so, but as I already tried everything and from customer support the solution they gave me was to add an offset or to use an external software to transform the data before the 3d-model construction... I will tray everything to make it work.

By the way, from custumer support, they suggested to use "control points" to get the right heights but it didn't work as control points are used for accuracy issues, and here I'm traying to use a differen goid.

They also suggested to use the "seven parameter transformation" but I haven't tried yet.

Thank you everybody fo your suppot

Have you tried to post process your data using the free Emlid Studio program, then take the WGS84 .pos file it generates and convert the values to your projected model using a program like global mapper, then importing the converted .pos file into DJI Terra after you import the photos?

The Version Number: 4.0.10 base position fix seems to only apply to lidar processing.

Sunister1 Posted at 4-12 08:43
Have you tried to post process your data using the free Emlid Studio program, then take the WGS84 .pos file it generates and convert the values to your projected model using a program like global mapper, then importing the converted .pos file into DJI Terra after you import the photos?

unfortunately this is not quite how you should proceed with a LiDAR. For photogrammetry this method is possible, yes. Although Emlid studio converts to ellipsoidal altitude only. So the problem remains the same.

The solution which consists of indicating a vertical offset remains the least worst. Use QGIS or something else to find out the geoid value at the location of your survey, and enter it in the box.

The story of the seven parameters, forget it, it's certainly someone who has no clue what it is or who hasn't understood the question, who answered that to you.

Sunister1 Posted at 4-12 08:44
The Version Number: 4.0.10 base position fix seems to only apply to lidar processing.

Indeed it is for the LiDAR post process. I did the test, what is certain is that now the change in coordinates is taken into account. So this is fixed.

On the other hand, I wonder how the calculation is done because by going through Emlid, I don't find the same results... it may be a bad setting on my part, I did this quickly.

If he were to edit the ellipsoid height of the rinex header position in Emlid Studio and insert the geoid height or orthometric for his base, would this not give him the correct altitude after processing?

Sunister1 Posted at 4-12 10:34
If he were to edit the ellipsoid height of the rinex header position in Emlid Studio and insert the geoid height or orthometric for his base, would this not give him the correct altitude after processing?

It can yes. If X and Y are correct. But it is not at all a conventional way to do that.

Rinex coordinate are ECEF, and that's it. Then they are usually translated to WGS for ease of use. But never you should modify the vertical datum here. It must be done after.

It could theoretically work if he is in a bind though.

Geoid Height Calculator link below.

https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html

Sunister1 Posted at 4-12 10:41
Geoid Height Calculator link below.

https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html

Most of country have there own national geoid, which has a legal value for survey work. But this link may be valid for US. I don't know.

That's a good point. He will have to look into it.