negative elevations in the digital terrain model

[Luiz Antônio Hugen]

Hello everyone. 
I respectfully greet everyone in the community and I already thank all help in advance. 

My problem is the following: when generating the DEM (digital elevation model) after classifying the dense point cloud, I am encountering negative elevations. 

I live in Brazil, and this particular work is in Santa Catarina, where the coordinate system is SIRGAS2000 UTM Zone 22S (EPSG 31982). 

From what I researched, Metashape does not have the datum we use, which would be HNOR2020 from Imbituba. 
While researching, I found that it is possible to download this datum and theoretically import it into Metashape, placing it inside the folder: 

"C:Program FilesAgisoftMetashape Progeoids" 

Following the path "Tools > Geoids" 
I can even import the file, however, I need to associate it with a geographic system, which seems strange to me. 

Well, my difficulty then is: how do I deal with these negative elevations, and is it possible to create or edit the coordinate system with the correct datum.

[Paulo]

Bom dia,

do you have the HNOR2020 geoid model? Can you share it so that I can show how to configure to use with SIRGAS2000 datum....

I have found the following geoid grid HNOR2020-1_brazil.tif from https://github.com/geoifg/geoids/tree/main.

To import, I use Tools/Geoids... and Import.... button, then select the above file. In Import Grid... dialog, I enter SIRGAS2000 for Geographic CS and Custom for Vertical CS. In Edit Vertical Coordinate System dialog, I entered info as in attached screen copy... Click OK  twice to close 2 dialogs and you now have the grid imported:

Code: [Select]

2026-05-27 15:37:44 Grid installed to: C:/Users/Asus/AppData/Local/Agisoft/Metashape Pro/geoids/HNOR2020-1_brazil.tif
Now you can create a compound CS incorporating the above geoid to your SIRGAS2000 UTM Zone 22S (EPSG 31982). Edit it as in 2nd screen capture...

You now can use the CS: SIRGAS 2000 / UTM zone 22S + HNOR2020 height  in your project...

Espero que isso ajude!

[Luiz Antônio Hugen]

Good morning, Paulo.

Thank you very much for your response, it was very valuable, as it confirmed that the process I have been trying to do is correct.

The models I downloaded were exactly from this GitHub link you attached, and I also took the opportunity to download the mapgeo2015 one, although it is already an "obsolete" model, it might be useful at some point.

Perhaps the reason I couldn't import the HNOR2020 file into Metashape is because where I work it is necessary to have the administrators' password to move a file into a folder, as in the case of the Agisort folder:
"C:Program FilesAgisoftMetashape Pro"
So, probably that caused some "error" that made it seem to me that the process had not been completed successfully.

Today I managed to move the file into Metashape's native folder, but when performing the process to import the HNOR2020 file, I ran into the following error, as shown in the first attached image.

It is probably my level of access to the Metashape folders that is causing me this kind of problem.

But I will keep trying, thank you very much for your attention.

[Paulo]

Yes Luiz, I guess to have access to main geoids folder "C:\Program Files\Agisoft\Metashape Pro\geoids", you should run as Administrator....