I have a model that was modified in Maya for substance textures.
I exported it from Maya 2024 to USD, then imported into Houdini.
The geometry where there are slots looks fine in OpenGl, but when I try to render using Karma, I get these strange geometry artifacts.
The image called Houdini_USD_unpacked_obj_context shows the unpacked geometry in obj context. The geometry and UVs look fine.
The image called StageContext_OpenGL shows the geometry imported from obj context to stage context. Looks fine in OpenGL.
The image called Karma_GeometryArtifacts shows these strange geometry artifacts that are partially covering the slot-shaped holes.

Any idea what's causing this and how to fix?

I tried to use a Clean SOP in the obj context, toggling all the options, but no change.

Thanks

In the meantime, I found a workaround.
I use the PolySplit SOP to divide the large flat polygons around the hole into smaller polygons.
Which is time-consuming and labor-intensive.
Maya and Arnold are able to render the original geometry without this problem.
I'm curious to know why Karma has issues with it.

In general it's not good practice to leave geometry as ngons, especially if the mesh has holes. Aside from giving some renderers trouble it can also cause issues with geometry interchange. For example, certain importers will simply ignore ngons and leave you with missing faces.
If you can, triangulate ngons in Maya. Otherwise fix it in /obj or a SOP Modify in LOPs. One way is to create a group with the Group Expression SOP and the expression @numvtx>4, and then run that group through a Divide SOP (enable Avoid Long Edges). This will leave your quad topology alone and only triangulate the ngons.

Siavash Tehrani
In general it's not good practice to leave geometry as ngons, especially if the mesh has holes. Aside from giving some renderers trouble it can also cause issues with geometry interchange. For example, certain importers will simply ignore ngons and leave you with missing faces.
If you can, triangulate ngons in Maya. Otherwise fix it in /obj or a SOP Modify in LOPs. One way is to create a group with the Group Expression SOP and the expression @numvtx>4, and then run that group through a Divide SOP (enable Avoid Long Edges). This will leave your quad topology alone and only triangulate the ngons.

Thanks, Siavash. I'll give your suggestion a try. This is an old model by a volunteer while they were still learning how to model in MAya. They wouldn't make that same mistake these days.
I'm just curious why the original geometry looked ok in openGL and in Arnold in Maya, but not Karma.