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Artefacts in deformation analysis
Posted: Thu Sep 21, 2017 1:34 pm
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?
Re: Artefacts in deformation analysis
Posted: Thu Sep 21, 2017 6:20 pm
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?
Re: Artefacts in deformation analysis
Posted: Thu Sep 21, 2017 7:52 pm
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
Re: Artefacts in deformation analysis
Posted: Tue Sep 26, 2017 5:44 pm
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)
Re: Artefacts in deformation analysis
Posted: Sat Sep 30, 2017 9:09 am
by Moja
Re: Artefacts in deformation analysis
Posted: Sun Oct 01, 2017 3:19 pm
by daniel
Thanks, I got them this time!
Re: Artefacts in deformation analysis
Posted: Sun Oct 01, 2017 4:09 pm
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 (94.78 KiB) Viewed 2126 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?
Re: Artefacts in deformation analysis
Posted: Sun Oct 01, 2017 4:41 pm
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)