Export as Quads

[astiglic]

I don't understand why is this not flagged more.
I was going back versions to find out why it does this, but still finding this a HUGE issue.
In latest version I can't export any serious number of quads to obj, because it just crashes meshlab.
The ply format doesn't have polygons option available at all.

I bring in a mesh with a big number of errors, fix them, now all quads, no double faces, vertices or anything.
And I can't export them as quads, because if I try to save them as obj, the meshlab just hangs forever.
If I export them as ply, I can't save the quads, because polygons option is always half transparent and not available.
I went few versions back, and still the same issue with exporting to ply format.

[lvk88]

Can you explain step by step what you did the provoke the crash, and maybe attach an example mesh?

[astiglic]

I did test this through and through. Any meshes created by Meshlab, work.
I'm hoping to find a way to create a mesh inside the Meshlab which doesn't work, so it would be much easier to test in the future, instead of just providing one externally made file.

[astiglic]

ML_IS_05.txt

Just rename the file to .obj...
Remove duplicate faces (should be 12).
Save...

[astiglic]

ML_IS_07_Sin_terrace.txt

Or try:
Filters -> Create New Mesh Layer -> Implicit Surfaces -> size of voxel 0.01, x,y,z from -3.14 to 3.14, function: z-0.25rint(4sin(x)*sin(y))
Saved as ply -> Instant Meshes -> default all the way, saved as obj.

[lvk88]

Ah yeah, I see what you mean, I can reproduce the issue with your attached example.

I will try to find some time in the next couple of days to have a look on the reason.

[lvk88]

Hey there again! I debugged into the issue but I don't have a solution so far, sorry. It seems that the issue is not even with meshlab itself, but in vcglib, the export logic seems to get stuck in an infinite loop roughly here:

https://github.com/cnr-isti-vclab/vcglib/blob/c94ef4e12e9ea3ae986d9af91005be8328d13719/vcg/complex/algorithms/polygon_support.h#L227

I'm not sure what to do with this, maybe some vcglib developer can help out here? @alemuntoni , do you know anyone?

[chenxiao111222]

I encountered the same problem, exporting quad mesh triggers core dumped

[lvk88]

Hey @chenxiao111222 , how large was the mesh that triggered the core dump?

[chenxiao111222]

Hey @chenxiao111222 , how large was the mesh that triggered the core dump?

A small quad mesh, has ~2000 vertices and ~4000 faces only.

[cignoni]

I should have patched the problem in the VCG lib.
Can you check if it works as intended in the latest build of the next version of Meshlab?
https://github.com/cnr-isti-vclab/QMeshLab/actions (binary for mac and win only up to now)

[lvk88]

@cignoni I tried the two obj files that @astiglic attached in his two earlier comments. I was using this build of QMeshlab: https://github.com/cnr-isti-vclab/QMeshLab/actions/runs/33380122588

• ML_IS_05 does not open, the console says Failed to triangulate OBJ faces with rapidobj: Triangulation error.
• ML_IS_07_sin_terrace opens, but when I switch on wireframe mode, the mesh is displayed as composed of triangles instead of quadrilaterals, whic is how it appears in Meshlab classic. Exporting the mesh from QMeshLab does work, but if I manually inspect the obj file, I see that the polygonal faces are exported as triangles, not as quadrilaterals.

[cignoni]

Inside the new MeshLab we support different I/O libraries. Some are more robust but slow, other are quite fast but fails in some cases.
Inside the menu Help-> I/O Plugins you can choose different options for loading obj files The default is rapidobj, but actually the vcg obj importer is more robust (but much slower).
Probably it would be useful when a io filter fails to remember the user the possibility of trying different options.
I confirm that rapidobj does not handle those file correctly.