create orthomosaic using imported dem

[cwm]

I'm trying to import a dem derived from lidar to use to generate an orthomosaic. I've imported it in the same coordinate system as the project (wgs84) but when I go to process the orthomosaic I get a "zero resolution" error.  Any thoughts on how to bring in an outside dem to generate an orthomosaic w/in metashape?

[dpitman]

An ortho-photograph is one in which each pixel contains both RGB values and XYZ values.  A DEM on the other hand carries no RGB value.  You should be able to bring in a .las from your lidar dataset and produce an ortho from that.

[Arie]

Hi cwm,
did you check the bounding box (region)? Try resetting it.
Cheers.

[dpitman]

Hey Arie,

By your reply, I take it that it is possible to create an ortho from a DEM.  Since I don't see anything about that in the manual, can you shed some light on the workflow? 

Thanks,
Dave

[cwm]

Hi Arie,

Thanks - I did try resetting it, same error.  There doesn't appear to be anything wrong with it, it shows tie points inside the bounding box.  A few at the edges are cut out but that's it. 

[cwm]

Hey Dave -
I'm just trying it use the lidar dem as the surface to project the RGB photos I have onto instead of relying on the photoscan dem creation.  That way I would be able to import the terrain surface and not use the top surface or rely on the ground classification algorithm

[dpitman]

Hey Dave -
I'm just trying it use the lidar dem as the surface to project the RGB photos I have onto instead of relying on the photoscan dem creation.  That way I would be able to import the terrain surface and not use the top surface or rely on the ground classification algorithm

Ah, you have photos to drape the DEM; Got it, thanks! 

Although not working, can you share the steps to accomplish what you're after.  For example, when I select a DEM in one of my projects, I don't see anything in a context menu that looks like using the image set in order to drape the DEM.  And in Tools > DEM, I only see the option to transform.

[cwm]

I just used the import option when you right click on the chunk name in the workspace.  Then I built the ortho using that imported dem.  I couldn't get it to work using the same coordinate system (wgs84) and when I tried using a different coordinate system I got some funky results like features from the images were being duplicated.  Thinks look pretty good with the dem created in phtooscan, but it would be great to have the ability to use a lidar dtm when available

[dpitman]

Thank you.  Before, I didn't notice the setting to use the DEM for the surface instead of the mesh.

Can you share an image comparing the look of the lidar DEM compared to the photogrammetry DEM?  That would be interesting.

[Arie]

Have you tried using a projected coordinate system (such as UTM)?
Which format are you using to import the DEM? Does it show up in the correct position?

[Alexey Pasumansky]

Hello cwm,

If you are sure that the imported DEM covers the same area as the cameras, please send the following data to support@agisoft.com:
DEM that you are importing, PDF report from the project (after aligning the images and importing the DEM) and the following archives from the project.files structure: project.zip, chunk.zip and frame.zip.

[cwm]

Thanks, Alexey.  I think I'm moving in the right direction.  I noticed in the report pdf the dem wasn't showing up and it dawned on me it's because I didn't have it in the same vertical units (ft instead of m) as the data.   I was so focused on the projection issue I overlooked that. 

Now the dem looks good in the pdf report and the orthomosaic processing starts but I get a can't open file warning. 

[Alexey Pasumansky]

Hello cwm,

Do you have any file synchronization/backup services running for the project files folder?

The provided message indicates that some other process is trying to access the archive file with some orthorectified images.

[cwm]

Thanks for helping, Alexey.  I keep moving in the right direction (I did have auto backup on).

 I've been able to import the dem and create the orthomosiac, but now still having the issue of repeating features on the output.  The resolution of my dem is 93.5 cm/pix while the orthomosaic comes out at 3.97 cm/pix if that helps identify the issue