STL performance and resolution

[JosefWN]

STL Reader:
I'm working with larger STL files (commonly binary files sized 100 MB - 2 GB). ANSA can deal with these files quite swiftly, but pythonOCC doesn't seem able to read them in reasonable time. After waiting 3 hours (python running at 100% CPU on a single process) to read a 200 MB STL I gave up. Are there known issues with STL reader performance? This is using the example code.

STL Writer:
Is it possible to control the sampling resolution for CAD files when they are saved as STL? Right now it seems to be done entirely automatically?

[jf---]

hi @Puffton ,

So, the OCC.STL module is a little awkward. What is does is that every triangle becomes a nurbs patch. Hence the very high cost of importing STL meshes. Now, SMESH offers an import such that the mesh is merely rendered in the viewport, and not reconstructed as a BRep type.

Personally, I've been using an approach where I use pyassimp while pushing the imported mesh to opengl like so

So in order to help you a little more precise its relevant to know what you're aiming for.
Do note that pythonocc's focus is on BRep geometry, not meshes...

[JosefWN]

Thank you for your quick reply @jf---! Currently I'm using pythonOCC to load files (IGES, STEP and STL) and outputting a scaled binary STL mesh. I'm not rendering anything onto the screen. Later me and my colleagues might want to use more meshing capabilities such as volume mesh creation from a clean surface mesh. Perhaps SMESH is the way to go for us then?

[jf---]

ah, OK I understand the problem a lot more precise now.

• not suprised about the poor STL performance...
• possible numpy-stl is more convenient if the operation is pretty trivial
• yes, so volumic meshing is what SMESH is all about
• here's an interesting post on SMESH and old one here
• the SMESH lib was recently updated, and the python wrappers need an update

[JosefWN]

Okay, thanks a lot for your help! Oh, and it would be cool if the precompiled binaries fetched with Conda included SMESH too (at least as an option, if that is possible)!

EDIT: Ah, this seems related to #289.

[tpaviot]

@Puffton The current master branch wraps smesh, an example of fast STL loading is here f8f3735

[tpaviot]

@Puffton can u please point me to a big STL file I could test the fast STL example ?

[tpaviot]

@Puffton With the current pythonocc-core master branch, based upon oce-0.18/occt6.9.1, you can set the STL file resolution by setting the mesh deflection value. I updated the STL example to show how to modify this parameter in order to change the STL file resolution see commit bb13189

[tpaviot]

Both STL performance and resolution issues are solved, closing this issue.