I'm trying to export an ABC from Houdini with instancing enabled. I have a bunch of regular packed primitives with a Cd attribute on the points, and they're being written out to disk just fine. Instancing enabled on the Alembic ROP makes these files very manageable.

However, if I try to read this Alembic back in, the Cd attribute is gone, even after unpacking. I need to be able to read this attribute as a color set if possible, so that I can use the Alembic in VRay. Is there any way to correctly write attributes to instanced primitives for Alembic export?

I'm using 16.5.439.

Same here - on 17.5 and 18. Did you find a solution?

No, unfortunately… I still don't have a good solution for this. I was trying to kick out Alembics with vertex color sets that I could read with VRay for Maya, while maintaining instancing. Alembic instancing isn't really instancing in the typical sense, it's more like “data-deduplication”, so it's still not the best solution compared to something like particle instancing.

Thanks! Mine's a meshed fluid sim and got around it by promoting Cd to a primitive attribute - that worked. Other attributes also get lost - like rest. Odd behaviour. :/

If you're trying to get a fluid sim across to render with VRay in some other software package, my advice would be to write the fluid out as an Alembic sequence (not a single Alembic file) and promote Cd to a vertex attribute. The VRayVertexColors node should be able to read that attribute by index if not by name. You can create a VRayMesh (what you'd use to load a VRay proxy) and point it to an Alembic file on disk, and it should read it as an Alembic procedural and read vertex attributes via VRayVertexColors.

Thanks! That's helpful info. I'm currently just doing some research for a possible future project to see what options there are, and at the moment checking if the data at least comes back into Houdini. Client will most likely need to use the geo in C4D. Not sure what renderer though. I think they mentioned Corona. I don't have C4D at the moment but vertex color, or something like that, sounds like a term I've seen in C4D before. Next step is to just run some tests with client.