OTOY Forums

Hello Juanjo,

i've been using TFD for a few days now and i come to a strange
bug in renders, there are some kind of a grid appearing,
more obvious on some parts of the image, i took a screen capture to show you:
These strange artifacts doesn't show up with regular VDB renders,
only with TFD.
Do you have any idea what could occur?
Reducing volume steps helps a little bit but needs insane render times,
and VDB renders never shows these artifacts, even at very low resolutions.
Also, TFD juste released a new build (1425), do you think it will work with
the last build of octane? They also released a VDB converter for TFD cache files.
Thanks a lot!

Olivier

Hi,

It seems a low grid resolution issue. Do you know if a VDB file from the same TFD cache has better resolution? Perhaps the internal Octane VDB processing supports some kind of interpolation not available exporting the grids directly from TFD.

If you want to send me the scene and one of the cache files I could test it here.

Thanks,
-Juanjo

Hi Juanjo,

i've just sent you the files via Wetransfer,
i made a few more tests, sadly the VDB file has the same issue,
and uprising the resolution of the render (i made a test at 6400*4800 pixels)
gave even worse results...
When looking closely to the preview of the TFD smoke in the layout view,
you can see this grid showing up, but not on regular LW renders.
Thanks again for your help

Olivier

Thanks for the scene. I'll check it later today.

Anyway, I know that TFD has tools to smooth and add detail to the base grid at render time, a feature not available yet in Octane. I suppose that this is the difference that you can see in the Octane renders. I suppose that the only workaround is to work with more dense grids.

Thanks,
-Juanjo

Hi Juanjo,

thanks, yes that's what i thought,
i did another test with a denser grid,
it stills shows up but as it's smaller
it's not so obvious at rendertime.
Anyway, thanks again,
just a quick idea : do you think you could test
the vdb file with Arnold?

Olivier

Other render engines have better voxel interpolation techniques to avoid these artifacts. For example the same VDB file rendered in Houdini with Mantra looks a lot better, but the grid artifacts are still there. Probably the GPU path tracers are not so good for this kind of grid interpolation algorithms.

Thanks,
-Juanjo

Thanks Juanjo,

i'll manage with denser grids for the moment,
but it must be done at the first simulation in TFD,
i noticed that up-res keeps the original grid artifacts size
(even with a high up scale).

Olivier