I'm curious why POPs has not integrated sourcing a velocity grid into its solver when providing a collision vdb with velocity grid (collisionvel). Ideally I want to simplify a setup by providing a single collision source and not include geometry. Has anyone hacked the solver using a sourcevolume?

Have you tried playing with the POP Advect by Volume SOP?

What are you trying to achieve? I assume that if you have a collision vdb, that it's been created from geometry. Is that not the case?

I have complex creature that needs to collide against a particle sim. I need the creature's velocities to transfer across. VDB collisions are fast when using DOPs applying them via a rbdobject (enabling volumes). I can also transfer my creature's velocity, but I need to wire the vdb source geom into the rbdobject as well. This step is roughly 5x slower. It could be avoided if the rbdobject could also sample the velocity on my creature's VDB.

I could advect the sim with the creature's VDB in POPs, but that's inaccurate as I want the velocity at the collision point. If the POPs solver allowed sampling of collision vdb's velocity internally, you'd have a correct velocity sample and it would be applied in the correct sim order. Less nodes, cleaner rigs.