Volume cache rendering in wrong place

[rustyippolito]

We have a pyro sim done in Axiom and cached out that is not rendering in Octane correctly. It appears perfectly in the Houdini viewport, however in the IPR or rendered frames it has been repositioned and/or scaled. We even tried rebuilding a super simple hip file that just reads in the cache and renders it and we get the same issue... anyone have any ideas? Here is a screengrab:

[juanjgon]

Your vdb object has grids with different voxel sizes (the density and temperature grids have 0.01, while vel has 0.02), something not supported by Octane currently. You can resample the velocity grid to match the voxel size of the other grids using the VDB Resample SOP, as shown in the attached image. Also, you should convert the "vdb" primitives to "volume" primitives to improve the scene extraction time, or even better, cache the volume sequence as OpenVDB files that Octane can load at the render time, making the scene extraction time almost zero.

Hope it helps,
-Juanjo

[rustyippolito]

Thanks for the lightning fast response! The VDB resample is the quick cure, now i will go hunt down where those different voxel sizes came from...

[rustyippolito]

I believe I found where the voxel size was being halved. It was in the Axiom output tab. Under Compression, the default settings have the Velocity scale set at 1/2. When we change it to 1/1 the velocity voxel size goes from .02 to .01, matching up with the density and temperature voxel sizes. Also wrote out vdb files directly and load times are WAAY faster! Thanks for the heads-up on that:)

[juanjgon]

There isn't anything wrong with remapping the velocity channel inside Houdini if you want to save disk space in your cache files, but anyway, yes, working with OpenVDB files is the right workflow while rendering animated sequences of complex volume objects. This is true for any renderer, not only Octane because all renderers usually can load OpenVDB files as procedural objects at the render time.

Thanks,
-Juanjo