Close a tunnel mesh

[Dann]

Goodmorning everyone! I need to close a tunnel mesh but haven't found a way. I'll explain well what my input data are and what I would like to get. I have a point cloud from a cave obtained from a laser scanner. My goal is to select only one section of the cave and on this to calculate the internal volume. I already know that to do this I need to segment the cloud, calculate normals and generate the mesh. To calculate the volume I need a closed mesh, without holes. This is where I can't find a solution, I can't find a way to generate a mesh that plugs the entrance and exit of the sectioned cave with a perfect plan. Can you tell me if there is a way and how to do it? Thanks everyone in advance!

[DA523]

1- choose your mesh
2- EDIT >> MESH >> SAMPLE POINTS
3- Choose new mesh sampled cloud

4- click SET-TOP VIEW
5- PLUGIN >> HIDDEN POINTS REMOVAL then click OK
6- choose new mesh sampled cloud
7- click SET-BOTTOM VIEW
8- PLUGIN >> HIDDEN POINTS REMOVAL then click OK

9- Choose the new 2 segmented pointsclouds
10 - TOOLS >> VOLUME >> 2.5D VOLUME
use
leave empty
proper grid size
in z directuin

please take care this approach does not work if you have more than 2 points with the same Z (ie more than 2 ceilings)

[Dann]

Thanks DA523 for your reply! I don't know if this method can work well due to the very complex geometry. You also told me that this approach does not work if you have more than 2 points with the same Z (i.e. more than 2 ceilings). Is there no way to calculate the tunnel mesh and then find the volume with Edit -> Mesh -> Volume? The two ends of the cave are cut according to a vertical plane (I am attaching a screenshot). Isn't there a way with other software to put a cap on the two ends in order to close the mesh and then calculate the volume? Thanks again. Any advice from you is greatly appreciated.

[DA523]

1- 2.5D volume is the best choice but does not work if more than 2 points have the same Z value (multilayers )

2- Edit -> Mesh -> Volume theoretically can calculate any solid mesh (watertight mesh) volume,however it is very sensitive to holes, nonmanifold and defective faces (wrong order of face points, etc)
(I assume that Mesh -> Volume does not use 2.5D algorithm )

3-Closing mesh is easily done with Blender (the best ), freeCAD or meshlab. but the closing process can generate sometimes a lot of nonmanifold and defective faces so CC can give a wrong volume without any warning

4- Meshing your tunnel pointscloud is the most difficult step ..
Did you get an acceptable mesh despite it being opened at both sides??
Can you post here the mesh in STL or PLY file? ore post some mesh similar to your mesh ..

5- Convex hull meshing by meshlab is a quick way to give a rough volume that is surely bigger than your mesh volume. This helps in case you just need max possible volume

again, Did you get an acceptable mesh despite it being opened at both sides??

[Dann]

Thanks again for your response DA523. I was able to calculate the mesh with other software. Unfortunately cloudcompare is a mess. With other software I can generate a discrete mesh on the whole file, not the sectioned one on the area of interest. This means that I have to cut the area of interest on the mesh but this does not generate a clean cut and it is a problem. I'm sorry but unfortunately I can't share the file, I would have gladly done it but they forbid me.
Also, by calculating the 2.5D volume I tried to follow your guide but the point cloud is not homogeneous, so leaving many empty spaces underestimates the volume. I could interpolate the cloud first with the rasterize tool but it's not easy with the cave geometry.

[DA523]

As I mentioned above, the most difficult job is to mesh your pointscloud correctly ..
Believe me, it is the biggest challenge
After that cutting section and closing both ends is possible with Blender

If you decide to use 2.5D volume and you meshed your pointscloud correctly then EDIT >> MESH >> SAMPLE POINTS (to10 million points) will solve the nonhomogeneity issue forever

[DA523]

I attached here an example about using HIDDEN POINTS REMOVAL with 2.5D volume
I sampled the mesh with 10k points because of the limit on attachment size
Please resample mesh with EDIT >> MESH >> SAMPLE POINTS (to 10 million points)
The real size is 11.2 cubic units
.

Group.zip

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