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Some GEOM module operations are very slow with many surfaces

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Some GEOM module operations are very slow with many surfaces

Posted by Massimiliano Leoni at February 25. 2021
Hello! Similarly to my latest thread, I am working with a geometry which I have in STL format. I want to define groups of faces for this geometry, but every step takes very long. To reproduce this: Set-up 1. Open Salome and create a cube in the GEOM module [or anything] 2. Go to the MESH module and mesh that cube [triangles, surface only] so that you get around 20'000 faces 3. Export the mesh to STL 4. In the GEOM module load the exported STL Execution 5. Right-click on the loaded shell, select "Create group" 6. Under "Shape type", select faces Here Salome starts hanging, and the operation will take a long time to complete. I tried debugging/profiling this, please find a callgrind log at https://tinyurl.com/4hkkduva . From the log, and also from dumping the stack with eu-stack, it looks like most of the time is taken by SALOME_View::Display [called by GroupGUI_GroupDlg::activateSelection] which, to my understanding, has to do with updating the OpenCascade viewer -- please correct me if I'm wrong. Even if I wait until this operation is over, all the following ones [selecting cells manually, adding them, removing them, applying...] still take very long. Is there any way to avoid this overhead? What can I do about it? Don't hesitate to let me know if I can provide any further information Thanks for your help!

Re: Some GEOM module operations are very slow with many surfaces

Posted by Vadim SANDLER at February 25. 2021

Hello,

Unfortunately, GEOM does not well suit to work with meshes. Indeed, STL stores data as a set of triangles - it is in fact format to store mesh data, not geometry. It means that each triangle represents a separate face. When STL is imported to GEOM, resulting CAD model is a shell that consists of a large number of faces, even though they belong to the same (few) surfaces. GEOM is not optimized to work with the huge number of sub-shapes - some GUI operations (like creation/editing groups) automatically explode the shape to sub-shapes, to allow manipulating them (select, show/hide, etc). That's why the performance may be mad on such STL import.

Regards,
Vadim.

Re: Some GEOM module operations are very slow with many surfaces

Posted by Massimiliano Leoni at February 25. 2021
Hello Vadim, thanks for the reply. I do understand that that is the problem, my question was on whether there is an already implemented way around it. If there isn't any, I wanted to ask the developers if they would be willing to address this issue [by optimising GEOM to work with many sub-shapes]. I understand a thing or two of coding myself, so with some guidance I could try to fix it -- if there is an easy fix to try. Best regards, Massimiliano

Re: Some GEOM module operations are very slow with many surfaces

Posted by Vadim SANDLER at February 25. 2021

No, currently no improvements in this direction. And it is not easy to solve mentioned problems. On the other hand, I believe there should not be many problems working with geometry imported from STL in batch mode - i.e. via scripting.

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