Vray environment fog and Phoenix smoke

[ben_hamburg]

Hey there,

I´ve run into another issue when rendering phoenix smoke grid in volumetric mode with vray environment fog. I remember reading that that is an issue and
I can fix this by rendering in volumetric mode, but then render times are a lot higher, and they are already pretty high...
Is there another fix for this?

I´ve had good experience rendering everything in one pass for a different underwater shot, so I´d still like to do this way and don´t wanna go back to comping it...

Any advice on how to speed things up otherwise?

[ben_hamburg]

Left is with volumetric mode, render time: 2.22m, right is with volumetric geo mode, render time is 19.17m. And that is still very noisy and only 480X270 and no vraydisplacement...
If there is no other way I will have to try if I can render in volumetric mode and then color correct the volumetric atmosphere pass.
Final shot will also have DoF baked in, so I´m not sure that will work...

[ben_hamburg]

Hm, thinking twice...I´d have to render the volumetric smoke as an extra layer, just using the atmospheric element won´t work, since vray environment is in there as well of course...

[georgi.zhekov]

Hello,

What you can do is turn off the Environment fog and use a second Phoenix simulator in it's place. You don't need to simulate anything at all. Just make a big simulator where you want the fog to be.
Set the Smoke opacity to Smoke and set the left most opacity point to a value more than 0. This will control the density of you fog.
This way you won't need to set the render mode to Volumetric Geometry and it should render faster.

[ben_hamburg]

Oh, awsome, I´ll try that, thanks!

[ben_hamburg]

Hm, doesn´t seem to work. Any particular nightly I need to be on for this for it to work?

[georgi.zhekov]

Generally we recommend to use the latest one, but this should be working with the official builds as well.
What do you mean by it doesn't work? It's not rendering the fog one or the main simulator?

[ben_hamburg]

Its not rendering the fog simulator. I also don´t get a gpu preview. there is also vrayvolumegrid in the scene, but I turned that off in case it was interfering.
And I also played around with different values for the opacity curve, including disabling the "compensate for scene units" checkbox and switching from smoke to simple smoke.

[ben_hamburg]

Oh, wait I might have made a really stupid mistake...

[georgi.zhekov]

Here is a sample scene how this works.
Note that there will be no gpu preview for the fog simulator until you sim, but the rendering will work without caches as well.

[ben_hamburg]

hey, sorry, it was really just me being stupid...I created the empty grid in perspective view and it looked like it was around the camera, but it actually was just hovering above it, lol...
But hey, I love being stupid much rather than something not working....
That being said: I know its on the to do list for Vray (or at least it was), but this renders beautifully and sooo much faster than with Vrayenvironment fog, its perfect if you don´t need render elements for the sims...

[ben_hamburg]

Ah, too happy too soon...
Apparently there is still some sort of Z-fighting going on.
Not sure if it is because the simulated fog is a VrayVolumeGrid and the environment fog a Phoenix Grid.
I´ll try it out again with two phoenix grids.
Any ideas until then?

[joconnell]

Definitely putting this in my notebook for volume passes in smokey corridors

[Svetlin.Nikolov]

Hey ben_hamburg

Two Phoenix grids are okay - a Phoenix and a volume grid is the same limitation as Phoenix and an environment fog - they are two atmospheres and atmospheres don't blend - you need to set one to volumetric geometry mode.

Cheers!

[ben_hamburg]

Ah, dang...but I should be able to render the houdine VDB via a phoenix grid, instead of the volume grid, which I´m doing now, right?
Just gonna try it out...