Phoenix VDB & Volumetric Shader

[NorthVisualStudio]

Hi

I'm trying Phoenix FD but can't post to the forum because I am using the trial. Hopefully it won't be a problem asking it here.

I have generated a large smoke sim and rendered it on the left then imported the VDB files using a Vray Volume Grid but the resulting render is on the right - they both use the same volume shader shown. Firstly, am I doing something wrong or is this normal?

Thanks

N

[Gosho.Genchev]

Hey there! Both should render the same assuming the Volumetric Shader settings are equalized.

If you're using one of the Phoenix FD presets (Large Smoke maybe ?) be aware that they set up some volumetric shader parameters.

You could try saving a render preset from Phoenix FD Simulator -> Rendering -> Render Presets... button and loading it over your Volume Grid from Rendering -> Render Presets... button. I know you've mentioned you've equalized the settings but it's the fastest way to make sure.

[NorthVisualStudio]

Amazingly that worked, no idea why because I thought I'd entered the exact same settings - thank you !

[Gosho.Genchev]

When you load a preset you get a prompt giving you the option to see what the changes made to the shader are. If you'd really like to know, you can check those.
Just to clarify - there are no hidden parameters that we set up - it's possible to copy the values manually if you're really careful. I guess you've missed something by accident That's why we have the presets in the first place.

Cheers!

[NorthVisualStudio]

I'm getting some strange splotches on my clouds, is this a sim or render thing?

[LarsSonparsson]

Decrease the light cache value in the Phoenix render settings. Try 0.5 or 0.3. If it still doesn't look good, turn it off

[NorthVisualStudio]

That's it, thanks !

[NorthVisualStudio]

Can a VrayEnvironmentFog and a Volumetric Grid be rendered together ? It seems that one or the other but not both together, hopefully I'm missing something. I'm using Vray Next GPU.

[Gosho.Genchev]

Yup, you can do that but you need to set the render mode for the volume grid to Volumetric Geometry (Rendering roll-out).
Maybe a developer can chime in with a more technical explanation but the way I understand it - V-Ray can't determine the order of the volumetric effects along the ray's path when multiple volumetrics are stacked one in the other.

Hope that helps!

[NorthVisualStudio]

I can't get it to work with GPU - it shows during the Light Cache pre-render but when rendering the EnvFog disappears.

[georgi.zhekov]

Hey, unfortunately rendering environment Fog and VolumeGrid together on the GPU is still not supported, but you if you use Phoenix you can make two grids one smaller where you have your main sim and one larger (it can be really low res and doesn't need simulation). For the larger one - from the Volumetric options - disable the rendering of the Fire and for the Smoke opacity choose the Smoke channel - then the curve will become active, adjust the left (the first) point so that it has a small value of 0.1 for example. This way the larger simulator will act as environment fog and the curve point will control it's density.