Artefacts in deformation analysis

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Moja
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Joined: Thu Sep 21, 2017 12:40 pm

Artefacts in deformation analysis

Post by Moja »

Deformation analysis of two epoch with three registrated scanner positions(for each epoch).

I get a result with cryptic artefacts like this:

https://imgur.com/gRdm8Rw

Any ideas?
Attachments
wall.jpg
wall.jpg (250.27 KiB) Viewed 2168 times
Last edited by Moja on Thu Sep 21, 2017 7:59 pm, edited 1 time in total.
daniel
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Re: Artefacts in deformation analysis

Post by daniel »

Interesting pattern!

Are the coordinate very big maybe? (and you didn't apply the Global Shift?). Otherwise it may be due to artifacts in the scanning process, but it's generally not 'regular' so it's clearly confusing...

Can you share the clouds with me?
Daniel, CloudCompare admin
Moja
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Joined: Thu Sep 21, 2017 12:40 pm

Re: Artefacts in deformation analysis

Post by Moja »

Thanks for your fast reply. The point size is default(small). Yes the global shift between both epochs is applied. Possibly a scaling problem (visualization)?

Here you can find the single database of the wall (.bin) illustrated in the image:
https://uni-bonn.sciebo.de/index.php/s/oay8SgTy6sOeJRr

... and here the whole dataset with some elements more. Shadowing can't explain the artefacts (specially at the top).
https://uni-bonn.sciebo.de/index.php/s/2DirO6qtxpCsPv4
daniel
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Re: Artefacts in deformation analysis

Post by daniel »

Oops, sorry, it seems I waited too long before downloading the files. Can you send me new links? (here or at cloudcompare [at] danielgm.net)
Daniel, CloudCompare admin
daniel
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Re: Artefacts in deformation analysis

Post by daniel »

Thanks, I got them this time!
Daniel, CloudCompare admin
daniel
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Re: Artefacts in deformation analysis

Post by daniel »

After several tests (C2C distance with or without local modelling, M3C2 distances, density computation, etc.) I didn't detect any 'algorithm' artifact.

The pattern has nothing in common with the octree (see image below), nor with the density pattern. And its magnitude is quite important (0.001 --> much bigger than the typical numerical computation accuracy which is around 1e-6 or 1e-7).
cc_artifact_against_octree.JPG
cc_artifact_against_octree.JPG (94.78 KiB) Viewed 2088 times
Therefore this pattern must clearly be already 'in the data'. Have any other pre-processing been applied to the clouds prior to the distance computation?

And how many scans are overlapped in this region?
Daniel, CloudCompare admin
Moja
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Joined: Thu Sep 21, 2017 12:40 pm

Re: Artefacts in deformation analysis

Post by Moja »

Yes, the clouds are unified with cyclone.(maybe the reason for the artefacts)

8 scans from 4 positions, but the overlapping areas are different.(so i suppose that this is not the reason)
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