Hi,

I would like to know is there a way to import local geoid Polish pl_gugik_geoid2011-PL-EVRF2007-NH (https://cdn.proj.org/pl_gugik_geoid2011-PL-EVRF2007-NH.tif) into DJI Terra? Why tere are some geoids in the Terra DB and some are not? Please, consider importing local geoids - life would be easier then.


And also, I would like to know how to handle L2 LIDAR reconstruction in terms of height offset of the geoid over ellipsoid? I can read in CDN.proj.org for my region of interest that the offset is +41.13 m. So I input this into Terra Height Offset field, setting geoid to default and horizontal DS as EPSG:2177 Poland CS200 zone 6, which is basically what I need. And I receive results like 70 m above real orthometric (geoidal) height. Which is more true for the flight height over the terrain in that particular task, but deffinitely not the ground height to the datum. Why?


Seems like only GCPs provided with right geoid height make the thing work. Shouldn't it be at least close to the right values providing the right Height Offset? Without GCPs?


Counting on reply and staying full of hope this is the right sotware and workflow,

Marcin

This geoid is outdated and from an unreliable source.

Also I'm not sure if importing into Terra works anymore. DJI never been able to do it properly.

I attach the correct official geoid as a zipped attachment, with a link to its source :


Model_quasi-geoidy-PL-geoid2021-PL-EVRF2007-NH.rar (1.18 MB, Down times: 0)

2024-12-9 Upload

Click on the file name to download attach
Model quasi-geoidy PL-geoid2021 modelem obowiązującym - Główny Urząd Geodezji i Kartografii - Portal Gov.pl


Also it is not possible that you have a point above the elipsoid in Poland. So the valid operation is more likely -41.13m. instead of +
But be careful because it is a botched job to do this. Because -41.13m may be true at a given location, but 1km further it is most certainly clearly different.
-> DJI Products EXIF Wrong Altitude / How to solve it | DJI FORUM


The correct procedure is to do the reconstruction with Terra in the local horizontal CRS of your choice and leave the vertical in WGS84 (ellipsoid).
Then either you generate rasters and with the raster calculator, from QGIS for example, you do raster - geoid, or with the point cloud and tools like Geocalc or Metashape you shift the point cloud according to geoid.

You can try these two. There is the one you want to use, the one from 2011, and the current one from 2021.
You open the PRJ when choosing the coordinate system and according to the manual it should work.
Spoiler, it doesn't work for me.

PL_2021-2011_PRJ.rar (1.5 MB, Down times: 0)

2024-12-9 Upload

Click on the file name to download attach

LV_Forestry Posted at 12-9 09:58
This geoid is outdated and from an unreliable source.

Also I'm not sure if importing into Terra works anymore. DJI never been able to do it properly.

You are right about geoid version to be officially used - since april 2022 geoid-2021 is valid.

Importing does not work anymore - there is the database prefed by DJI I guess. Hence, my inquiry directed to DJI officials - when, if at all, will it be possible to add / import local geoids in Terra?.

According to my understanding and knowledge, the geoid in Poland is above ellipsoid WGS84 mostly in range of 22-40 meters. But indeed, talking about ellipsoid height the equation I found (https://pl.wikipedia.org/wiki/Undulacja) is h = H + N, where h is ellipsoid height, H is orthometric heights and N is undulation, which is positive in this part of Europe. But you may be right, that in Terra when searching for H (orthometric height) we shall provide H = h - N, then we need to subtract undulation offset / value from ellipsoid height.

I will try to follow your workflow. As far as I work with 200x200 m areas I use PROJ.ORG, but  for wider ranges I would need right geoid rather ora at least right calculations.

Thanks for your reply. Hoping to hear from DJI on possible developments and updates of Terra in terms of LAS pointcloud registration and geoids.