Netgen OCC geometry "disappears" when cutting

Dear community,

Using OCC,I want to create (and ultimately mesh) a 3D spiral with cuts along the outer edge. This works fine when my spiral has two revolutions or less, but when the cutting geometry intersects the spiral a third time, the whole geometry seems to disappear. At least I cannot see it in the webgui. I have made a MWE [1] which hopefully makes the problem clearer. Observe that whether or not the MWE produces the expected result depends entirely on the value of the parameter named ‘revs’.

Thanks in advance for any assistance!

[1] MWE_occ_cut_spiral · GitHub

Best regards,

Hi Sindre,

I can confirm the problem, for recent OCC versions from 7.6 to 7.8.
I believe that the problem is coming from the OCC modeling algorithms.

For debugging, I propose you remodel the geometry using the OCC C++ interface. There are also more parameters available which are not ported to the Netgen-OCC interface.

Here is an example, taking the C++ - modeling of the bottle-example from the OCC pages, and return the final shape to the Netgen-gui.
Most of Netgen-OCC-Python wrapping you can find here:

If the problem remains you may contact the OCC - forum.

best, Joachim

BottleFromC++.ipynb (1.6 KB)
OCCBottle.cpp (7.2 KB)