Visualising Corrosion

[PointCloudEnthusiast]

Hello, I would greatly appreciate some insight into something I working through currently. Using a DSLR camera and Agisoft Metashape, I have two point clouds of a cylindrical concrete block (shown below), one taken after the block has been put into a corrosive bath (above) and one before it was corroded(below). I am trying to figure out a way to visualise the corrosive change that has occurred using CloudCompare.

Screenshot 2021-09-09 033540.png (768.63 KiB) Viewed 1661 times

Screenshot 2021-09-09 033556.png (841.45 KiB) Viewed 1661 times

I used the Cloud/Cloud distance tool to measure the change between the 2 point clouds. The result is below.

C2C.png (403.3 KiB) Viewed 1661 times

I also calculated the roughness coefficient of both point clouds and tried to compare them. (above = pre corrosion, below = post corrosion).

PreCorrosion_Roughness.png (270.02 KiB) Viewed 1661 times

PostCorrosion_Roughness.png (275.52 KiB) Viewed 1661 times

Unfortunately, when focusing on the whole block, the results seem to smooth over the areas where corrosion occurred. When I cut out a segment which I know has undergone corrosion, the results seem to scale to that. Below is a case of this where I calculated the roughness of a segment of the block.

Screenshot 2021-09-09 035950.png (321.43 KiB) Viewed 1661 times

Is there a way for me to cut out the same segment in both point clouds? Also is there documentation elaborating on how roughness itself is calculated beyond the wiki page (Particularly on how to choose a good kernel size)?

Finally, is there a better way for me to visualise the corrosion change than what I have tried currently? If so, would somebody mind pointing me to it?

Thank you for reading my message.

[daniel]

So first, since you are using Agisoft, don't you have meshes as well? Using cloud-to-mesh distances would be better (since they are signed, and there's no issue with point cloud sampling, etc. - even if you have pretty dense clouds here, but it's more 'by principle').

Then, you can definitely segment two clouds or meshes at the same time (just select both before using the scissors tool, or the Cross section tool). Just make sure you use a recent version of CC.

It's also important to define your own 'absolute' color scales when doing this kind of work. So that the colors are the same whatever the cloud is (so that there's no automatic 'scaling'). See https://www.cloudcompare.org/doc/wiki/i ... es_Manager

Then to answer you other question: the roughness is really as simple as what is explained on the wiki (the distance of each point to the average plane computed on its neighbors). Deferent radii will give different roughness estimates.

[Amaljith]

Hi sir I'm new in Cloudcompare.
I have the point cloud data of a cylinder from ID side in .e57 format. I have the original diameter of the cylinder. So I want to check for any diameter changes with colour scale. Is it possible in CC?Please help if its possible. It would be great if you can share some video tutorials or screenshots.
Thank you in advance.

[PointCloudEnthusiast]

Thank you very much for the reply Daniel. I will have a go with the meshes as well. Just to confirm, do you think measuring distances is a better way of visualising the corrosion than the roughness method I attempted?

[daniel]

Well, at least it's easier to interpret.