Cross sections of several similar clouds

[AliceKerr]

Hi,

I am trying to compare ~6 clouds of the same section of rock, each one slightly different (with a hole in the rock getting progressively deeper into the wall). I have managed to segment, align and register the entities of the clouds (I think) by following the tutorial online. I now want to do a number of things:
1. Work out the difference between the clouds - I think I may have managed this using the cloud to cloud comparison tool, but am not sure...
2. I also want to create a cross-sectional line along the same point through each of the clouds, so that I can have a series of cross sections showing how the rock has changed over time - is this possible?

Thanks!!

[daniel]

Hi,

1. Well, of course the 'Tools > Distances > Cloud/Cloud dist.' should indeed be your starting point (along with the wiki: http://www.cloudcompare.org/doc/wiki/in ... omputation). If you use always the same 'reference' (the initial state of the rock I guess?) make sure that its extent is wider than the others (if possible). Make also sure that its density is regular and quite high. If not, you should use a 'local modelling' strategy. Or even better, you can try to compute a mesh from this cloud and use it as reference. Don't hesitate to ask more information about all this (and post snapshots so as to make things clearer ;).

2. Here's what you can do:

• quick and dirty: use the use manual segmentation tool (scissors icon) with all clouds selected at once. Then rotate the clouds in the right orientation and use the rectangular polyline (click on the 'down arrow' next to the second icon) to make a thin slice of all clouds at once.
• use the cross section tool. Sadly this tool only works with one cloud at a time so you'll have to repeat the process for all clouds! The good point is that with the 'advanced editing' mode you can setup an absolute clipping box so as to use the same on all clouds (and with a controlled thickness, etc.).

[AliceKerr]

Thanks for such a quick reply :)

With regards to the cloud to cloud compare tool, the computer doesn't seem to let me select this option - it will only let me to mesh-cloud comparison - will there be a reason for this?
Also, when trying to use the cross section tool - it will not allow me to select this option either? I can do the shorter way - selecting all clouds - but when I am trying to segment the clouds, the program is telling me to define and or close the polygon, which I thought I was doing by right clicking..

The files originally uploaded onto cloud compare are .obj files, I think this is correct? I'm not sure why the above options aren't working...

Sorry for al the questions and my general incompetence,

Thanks!

[daniel]

Ah! It's because OBJ files contain meshes and not clouds. The good news is that you won't have to bother with the reference density, holes, etc. if it's already a mesh.

With meshes, you'll have to use 'cloud/mesh' comparison instead. Just be sure that the 'compared' mesh has enough vertices (in which case you can directly compute the distances between those vertices and the reference). Otherwise you can use the 'Edit > Mesh > Sample points' method on the 'compared' mesh to get a very dense cloud and then use this cloud as the 'compared' entity.

[borbog]

Hello, i would also like to see a cross section through several point clouds. it it somehow possible? the button dissapear when i select more than one cloud...

thanks and best regards,
boris.

[daniel]

That's not possible yet. It's in the TODO list though (so maybe in a future version ;).