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Author Topic: Wonky DEM of scanned images  (Read 1360 times)

sfrederickson

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Wonky DEM of scanned images
« on: January 16, 2023, 05:49:40 PM »
Hi there,

I recently ran the "generate DEM" process with a work project I am working on that consists of around 4TB of scanned aerial images. The process took weeks to complete, and when completed, most of the DEM looks great expect some specific parts where it obviously differs based on the flight path of the photos.

I created a mesh and point cloud prior, and everything looked fine before I ran the DEM process.

Does anyone know why these streaks appear?

Garfields_Lasagna

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Re: Wonky DEM of scanned images
« Reply #1 on: January 17, 2023, 01:09:50 PM »
Option A,
You should check the original images. I would assume that there is a difference in lighting/ exposure. This sometimes leads to changes in focus. And this can lead to blurry/ detailed DEMs. It looks to me like that.

Option B,
I also see that the overlap in this area is reduced or that the images are not homogenously spread. This can cause artefacts in a DEM.

sfrederickson

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Re: Wonky DEM of scanned images
« Reply #2 on: January 17, 2023, 05:35:14 PM »
I'm guessing that the issues I'm having are more of option A. Is there a fix to this or a step I should've ran before generating the DEM?

Alexey Pasumansky

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Re: Wonky DEM of scanned images
« Reply #3 on: January 17, 2023, 05:39:44 PM »
Hello sfrederickson,

I can also suggest to check, if the alignment is solid in the problematic area or if it looks like two overlapping, but isolated tie points. You can use View Matches dialog to check the number of tie points for some cameras with the other neighboring cameras in the area.

Also please specify, if you have masks applied to the non-imagery part of the scanned photos (like auxiliary info and image frame)?
Best regards,
Alexey Pasumansky,
Agisoft LLC

sfrederickson

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Re: Wonky DEM of scanned images
« Reply #4 on: January 17, 2023, 10:55:58 PM »
Hi Alexey,

Just confirmed that the non-imagery parts of the photos are masked.

Attached is one of the photos in the "strip" that looks different.

I've never used this dialog box before, should I omit the phots that have many "invalid" points?

sfrederickson

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Re: Wonky DEM of scanned images
« Reply #5 on: January 26, 2023, 10:50:33 PM »
Hi Alexey,

Just wanted to follow up on this.