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Author Topic: Why is cloud and DEM so distorted from simple dune-like texture?  (Read 3590 times)

2bForgotten

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Hi there,

Quite novice to Metashape and trying some features I ran into this problem:

I have a small project with sandy structure. Pictures are taken with drone and quite good quality camera (Sony Alpha) (70% and 80% overlap).

When I try to build a dense cloud, a rather unstructured/distorted surface emerges from pictures that show more or less flat sandy surface. The distortions are both above and under the actual surface.
The DEM will be equally rough when generated, whereas I know and see on the photo's that the surface should be nice and flat.

I tried cleaning and shaving the sparse cloud and camera optimizations but it doesn't seem to help.

Is there something I am missing or is the standard workflow (from manual. I tried both aggressive and mild depth filtering) inappropriate? Or is there a way to edit or accomodate for the phenomenon?

image_1 = dense cloud
image_2 = one original photo

Regards,
« Last Edit: May 31, 2019, 03:53:26 PM by 2bForgotten »

Jose Goncalves

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Re: Why is cloud and DEM so distorted from simple dune-like texture?
« Reply #1 on: June 04, 2019, 12:58:48 PM »
Hi
You'd better compare the original image with the orthomosaic, instead of the vertical view of the point cloud. The lack of patterns on the sand can contribute to a more noisy DEM. Always look at a shaded relief image of the DEM to assess its quality. You get better results with the sun at a smaller altitude angle.

Regards

José Gonçalves

PROBERT1968

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Re: Why is cloud and DEM so distorted from simple dune-like texture?
« Reply #2 on: June 04, 2019, 06:10:33 PM »
when you ran the dense cloud, what does it look like before you run DEM ?  Have you tried smooth Dense  cloud a little bit and what was the result ?

2bForgotten

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Re: Why is cloud and DEM so distorted from simple dune-like texture?
« Reply #3 on: June 05, 2019, 10:23:33 PM »
Hi
You'd better compare the original image with the orthomosaic, instead of the vertical view of the point cloud.
José Gonçalves

Hi there,

Yes it seems that the lack of contrast might be the culprit.
Is there a way to accomodate for it so that the DEM I want to create won't show those disturbances that I now see in the dense point cloud?
I now have included a transection of the area so you can see what my problem is.

Regards,