Resimulating OpenVDB?

[ben_hamburg]

Hey there,

I´ve started collaborating with some houdini guys for my short film on shots I don´t have time for or that are difficult to do with Max tools (including phoenix), like rigid body to liquid interaction.
I´ve successfully imported a single OpenVDB file and rendered it via VrayVolumeGrid, but now I´ve stumbled about this in the phoenix manual:

In case you want to render using motion blur, or resimulate over the imported cache, you must have the velocity channel exported as well.

Does that actually mean, that once I´ve got a complete sequence with velocity exported from houdini, I could then resimulate that with higher grid resolution, potentially saving tons of GB of cache space?

Somehow I can´t believe that, but if its true...is that all there is to it, or what are other issues I might have with this?

[Svetlin.Nikolov]

Yes and no - right now you can resimulate only over fire/smoke caches, since VDBs are missing the FLIP particle data.

However, for resimulation you need to have the same scene setup with sources etc., which might not be trivial.

[ben_hamburg]

Oh, that could partly work out of the box then, since I´m only concerned about smoke/pyro sims right now. And all the meshes come from my side already via alembic, so scene setup should be identical. Only thing missing are the sources and turbulences and what ever he uses in houdini, I just thought with velocities exported I might not need any sources and noise fields etc. if I just wanna uprez the OpenVDB sequence...

[Svetlin.Nikolov]

Ah, well, the resimulation just uses the velocity field from a cache sequence to drive a new simulation, so you would need to emit the smoke, temperature, etc channels. Turbulences are not needed though - anything contributing velocity is ignored by resimulation as is uses the velocity from the caches...

[ben_hamburg]

Ok, so in theory, If I get a houdini OpenVDB sequence with all those channels included, I could just uprez it in phoenix via resimulation (and all the correct meshes)?
Sounds too good to be true...