Hi everyone.

I am rather new to Houdini but managed to build a working FEM simulation and to write it out as alembic to render it in c4dtoa. However I am striggling to get a proper motion blur. After some researching I found out that I need to write the velocity attribute to the alembic so arnold can read it.
I guess the trail node creates the velocity attribute, but how do I tell the alembic rop node to write it out?
Any help is appreciated!

Thank you!

The alembic rop outputs all attributes by default. Unless you have specifically disabled the attribute, velocity should exist in the export.

Ok, then how do I access it in other programs? If I try to render the .abc the motion blur is always in a diagonal angle and always the same amount, so something has to be wrongly interpreted or wronly written?

Hey, maybe this thread could help you:
https://www.sidefx.com/forum/topic/44006/?page=1#post-197149 [www.sidefx.com]

jsmack
The alembic rop outputs all attributes by default. Unless you have specifically disabled the attribute, velocity should exist in the export.

Hey, in my case it doesnt somewhow.
I have a dopimport node that fetches the geometry. This node has the v Attribute. However when I plug it into an alembic rop, export it and reimport it, its not there…

The Geometry tab of the Alembic ROP has the list of exported attributes, by default it should be *. Is your value somehow different?

no its just the *
Am I doing something wrong with the connection maybe? dopimport to rop_alembic is fine?

No, it should be working.

Are you reimporting it as Alembic delayed load primitives? In this case you'll have to unpack it to see the attributes.

Or do you somehow have more than one v attribute (points and vertices, for instance)? Alembic won't like that.

My dopimport has the following attributes: baseP 3flt (pos), P 3flt (pos), pointlocation int64, v 3flt (vec)

I don't suppose you could share a scene file?

wrote you a pm

I think I fixed it, had to set the alembic rop to write out the v attribute on the vertexes instead of points and delete the v from the points. Also disabling motion blur on the rop_alembic was necessary to get a clean result in c4dtoa.

Sounds good!

Hey there, iam struggling with the same Problem. But Redshift.

Alembic file written out with velocity via trail. Checked all steps. In Geo Spreadhsheet also iam on the good side.
Inside C4d still no Redshift Motionblur working, besides a simple sphere made inside C4d works great next to the .abc file.

Would be happy about any advices.

Thanks