Tue, 01/31/2023 - 13:35
Attached you can find two STEP files exported from the same SolidWorks model.
example_split-periodical-surfaces.STEP is exported with the option “Split periodical surfaces” set.
example_nosplit-periodical-surfaces.STEP is exported with the option “Split periodical surfaces” unset.
The option makes a difference for e.g. cylindrical holes but also for conical surfaces.
Specifically, it automatically exports two half cylindrical surfaces for each full cylindrical surface.
For conical surface we can also see, that they are split in halves.
It seems that GMSH (which is reading STEP files with OpenCascade) cannot mesh the STEP file with no surface split and it generate the error “Impossible to mesh periodic surface” for the conical surfaces.
I'm trying to identify the issue here.
Could it be, that OpenCascade misinterprets the BREP definition for the conical surfaces in the case of example_nosplit-periodical-surfaces.STEP?
Could someone thake a look at this file?
Many thanks
Alexandru
Fri, 04/07/2023 - 11:16
Seems that nobody can help regarding this issue.
I tried to explain it but may it's not clear?
If somebody has the slightest idea, that would be very helpfull.
Many thanks
Alexandru
Fri, 04/07/2023 - 11:46
Hello,
The "Other usage issues" section of the forum is viewed by experts not in the DE field.
I would be grateful if the following questions related to CAD formats and their processing could be created in the DataExchange section.
We cannot help with GMSH, but will investigate what is happening on your file. As the problem is reproduced with our mesh generator.
We will take a look at your file and come back with some details.
Best regards, Dmitrii.
Fri, 04/07/2023 - 11:48
Hi Dmitrii,
Many thanks for the help. Sorry for posting in the wrong section. I didn't realize that there is a better one.
Next time I'll consider this.
Best regards
Alexandru
Fri, 04/07/2023 - 12:22
gmsh is worked, when use freecad test!
Fri, 04/07/2023 - 13:04
Thank you. So I suppose it could be a GMSH issue. Might depend on the GMSH version or on the GMSH settings (type of mesher).
Fri, 04/07/2023 - 15:23
When the STEP file is loaded in Gmsh through OpenCASCADE (latest OCCT master or OCCT 7.6.1), two surfaces can indeed not be meshed.
Attached are 3 images showing 1) the full geometry, 2) one of the weird surfaces, and 3) the visualization mesh that OpenCASCADE itself generates using `BRepMesh_IncrementalMesh`. The mesh created by `BRepMesh_IncrementalMesh` is clearly wrong, which seems to indicate that the issue is indeed with OpenCASCADE - but maybe only in some versions?
I've isolated the offending surface in a BREP file (see attached "debugSurface.brep" file), so that you can inspect it separately.
Fri, 04/07/2023 - 16:23
Thank you Christophe for looking into this.
So after all it's not GMSH, it's OCC.
What can be done about this?
After all, those kind of surfaces are found basically everywhere in the CAD models of mechanical systems, since they are feaures of bore holes.
Thu, 04/20/2023 - 18:57
Sorry, for the delay,
I tried to make quick check, but it was not enough.
I created a new ticket, please monitor this one:0033368: Data Exchange, Step Import - Split periodical surfaces - MantisBT (opencascade.org)
Best regards, Dmitrii.
Thu, 04/20/2023 - 19:18
Many thanks Dmitrii.
I have high hopes, that it will be solved.
The issue is a true pain for me.
Mon, 07/17/2023 - 15:33
Has anyone looked into this issue?
Is there any progress in finding a solution?
Many thanks
Alex
Mon, 07/17/2023 - 15:58
Hello,
Ticket is still on analyzing.
Best regards, Dmitrii.
Sun, 07/30/2023 - 11:41
Could you estimate how long it will take to solve the problem?
Sorry for pressing, we have projects depending on this.
Thanks
Alex
Thu, 02/29/2024 - 11:52
Hello Dimitrii,
Any chance of seeing this issue solved soon?
Many thanks
Alexandru
Thu, 02/29/2024 - 12:57
Hello, unfortunately the issue is not trivial and currently it is out our plans for current maintenance(7.8.1). My apologies.
Best regards, Dmitrii.