Mon, 03/31/2025 - 18:51
Hello everyone!
When tessellating shapes with BRepMesh_IncrementalMesh we noticed that fillets on cylindrical or rounded solids have strange artifacts (see screenshots). This problem does not arise for rectangular base shapes (see last screenshot).
We have tried several parameter combinations for Deflection and Angle. On some parameter combinations we get properly tessellated fillets -- however this happens only rarely. Our tessellation code follows the one that Dmitry Pasukhin explains in this issue. The problem described in that issue may actually be related to the one we are encountering.
Does anyone have an idea whether this is a bug or insufficiency in OpenCascade or if we are missing something?
(We've tried several OpenCascade versions. This happens regardless of whether we export an STL from FreeCad or use our own tool.)
I attached the step file we created to investigate the issue as a txt file.
Mon, 03/31/2025 - 23:28
Hello. I assume the issue with the parameters. For having clear mesh for rounded solids better to have smaller angular deflection, could you please check which value do you using.
In CAD Assistant mesh is perfect. As an option, you can try to use external meshers, like Expres Mesh (OCCT) or some extarnal to find more sufficient mesh parameters each time.
But for sure, there are can be some relative incorrectency on OCCT side, but it is deep inside and diffuclt to detect.
Best regards, Dmitrii.
Thu, 04/03/2025 - 14:24
Thanks for your reply!
We are using angular deflections of about 0.26. I retested with really, really small value, like 0.01. This seems to help for the test-step file I posted, but it does not help with more complex files (which I am unable to share).
Apart from using the bounding box of shapes, do you have other suggestions how to choose the parameters?
Fri, 04/04/2025 - 13:17
Hi Jonas,
The screenshots make an impression that your mesh is not watertight (i.e. mesh nodes are not shared between edges).
This in its turn is a result of that your B-Rep is not a connected solid (or shell at least). So the first thing I would double-check is B-Rep topology. Mesher settings would be of secondary concern.
Good luck!
Roman
Fri, 04/04/2025 - 13:37
Wrong assumption, sorry. The STEP file was attached (and I missed that due to filename extension).The file translates to a connected solid and is triangulated/displayed just fine in DRAW.
stepread file.stp a
vinit
vdisplay a_1
vsetdispmode a_1 1
trinfo a_1
#or
incmesh a_1 2.59
trinfo a_1
triangles a_1
HTH.