I'm running into a situation where I have points in sops that i'm converting to a Points prim in lops, which should have zero points on particular frames. However, with how the lopimport works, the sopimport node doesn't create the Usd prim when there are no points.

The issue here is, now when I go to export that Points prim to a usd file, instead of having time samples on those frames where there's supposed to be zero points, it just grabs whatever points are present on the nearest frame (because of usd's interpolation).

How do I set up my sop data such that I can get a Points prim in lops with zero points? I tried using an add sop to create a ParticleSystem prim that would encapsulate the points, but that also seems to be ignored.

Does it work to create an empty points prim with a primitive LOP, and then layer the sopimport over that? I'm not sure how to get the Primitive lop to create the 'timesamples' for the points arrays instead of default values though.

This seems like something the USD rop should be handling, ie filling in timesamples for no points for frames that are missing the prim.

@jsmack the solution you describe is what we ended up doing to solve the original problem where we ran into this, however that was in a specific use case where we could anticipate what prims would be created by the sop data.

I can imagine other situations where we would not be able to preempt what will be coming out of sops, and am trying to get ahead of the curve.

chendryx
@jsmack the solution you describe is what we ended up doing to solve the original problem where we ran into this, however that was in a specific use case where we could anticipate what prims would be created by the sop data.

I can imagine other situations where we would not be able to preempt what will be coming out of sops, and am trying to get ahead of the curve.

I'd file a bug. I don't think the user should have to babysit the data like that for such a common situation.

Ok exploring this some more, testing with a more generic setup, it does seem like if you create an empty placeholder prim in sops, you will get a corresponding usd prim with zero points in lops.

My issue is that in my hda i am not seeing the same behavior. I'm gonna have to dig some more, see what specifically it is about my hda setup that is preventing the prim show up on the zero-point frames...

Ok narrowed it down, submitted an issue to support to identify if it's truly a bug. Example file attached - it's possible to create a Mesh prim with zero points, but you can't create a Points prim from sop data with zero points.

chendryx
Ok narrowed it down, submitted an issue to support to identify if it's truly a bug. Example file attached - it's possible to create a Mesh prim with zero points, but you can't create a Points prim from sop data with zero points.

Hi Chendryx, I just found your thread from some time ago and I think my issue [www.sidefx.com] is related to it. Did you get some more info from support? I will submit another report if necessery.
Thanks!

jarenas
Did you get some more info from support?

Yes I did get feedback from the support team, it should have been fixed as of 18.0.802. I just tested now in 18.5.783 and it does indeed seem to be fixed.