Threshold for weld-vertices, or welding vertices after openings?

[Moult]

Bug Description

I'm using weld-vertices which clearly has an impact, but there still are quite a number of elements which are still non-manifold (I've noticed they always have openings in them but that might be a coincidence). I can run a script / use Blender to weld again after the fact and it turns manifold, but this shouldn't be necessary, so I'm thinking either:

1. Either weld-vertices has a threshold which is lower than my welding script / Blender
2. or weld-vertices doesn't seem to apply after openings?

I use manifold checks for objects that we require volumetric take-off (e.g. steel weights, concrete volumes), because otherwise our volume checks are wrong.

Here's an example object, using Blender's 3D print addons to check manifoldness and to highlight the non-manifold edges.

Attachments

No response

Debug and Error Output

[aothms]

This issue has been reported before. Not sure if it's still open. Cursory search didn't find it for me. (chatgpt5 also didn't find it for me)

Some info:

weld-vertices has no threshold because that should not be necessary because meshing the topology should not generate new vertices. somehow this does happen in certain versions of occt (ideally we do an investigation which versions of occt are affected, because I'm quite sure this hasn't always been the case - there is a occt 7.9.1 already maybe it's already resolved; maybe we can create a one-off github actions workflow that builds occt using a matrix of occt versions; converts this file and checks manifoldness)

this doesn't actually affect quantity calculation as long as the orientation is still consistent, so a manifoldness check that incorporates some fuzziness is also an option, if we assume this issue will go away again in future versions of occt

[Moult]

For context I'm using util.shape.get_volume. I was under the impression that if it wasn't perfectly closed I'd get errors but I haven't actually checked (maybe as you say so long as orientation is good it should be fine). Thoughts?

I'm thinking of adding some util functions for checking manifoldness, or splitting into multiple islands of closed volumes (e.g. if there is an opening that splits the object into two) in case that affects volume calcs. Or deleting zero / degenerate faces. Or perhaps these utils are already available somewhere?

The usecase is we do quantities automatically and borky geometry gives borky results. The ability to check and/or heal would help.

[aothms]

Can you upload this or a similar file to https://github.com/IfcOpenShell/files/

I will create an action that runs various occt versions on the file and check for unique vert position count and then we decide what to do.