Vray Volume Grid - VDB setup guide request

[KushKush]

Hello Chaos Support team,

I'd like to ask if there a possibility to release in depth guide on how to set up Vray Volume Grid with VDB's. For those of us who like to use Vray for VFX.
- How does the gradients being calculated on different channels such as smoke/temperature and so on...
- Correct method of lighting for VVG
- Additional parameters that affect the quality of the VDB inside VVG.

I'm aware of some Chaos Group official tutorials on Vray Volume Grids but I feel like that those tutorials/guides could be improved.

Currently I'm facing issues such as lose of quality in smoke when comapred to render in Scanline render of Fumefx VDB.
I'm lighting the scene in Vray, so it makes little sense to me to render Atmospherics in different renderer and then hope to match it in post.

I have attached two images below, one is fumefx scanline and one vrayvolumegrid for comparison.
Scanline seem to have far more detailed smoke

[georgi.zhekov]

Hey,

Reagrding the different channels and how their opacity is being calculated depending on which channel you base them on you can find more info here - https://docs.chaos.com/display/VMAX/...pacity+Rollout

The green field in the opacity diagram in your screenshot represents the data range for the channel you have selected - in your case this is 0 to 150.

For the lighting - there is no right or wrong way to do it - usually using V-Ray Sun will produce the fastest rendering and will produce sharper shadows by default, while using lights with larger surface area or a Dome light will be slower and produce softer shadows.

From what I can see in your comparison shot - you have a directional lighting for the scanline shot, but you use a dome light or a very large light for the v-ray shot, which will make a lot of difference - since the smaller light will bring out more detail in the smoke.

In order to match the first shot, try equalizing the lighting first, then try using the Smoke opacity based on the Simple smoke opacity and try a value close to 1 since in your ref from scanline the smoke looks a bit denser - you can also try using the Smoke opacity based on the Smoke channel and use the curve ( try adding a new curve point in the middle of the curve and drag it towareds the left upper corner - this will make the smoke denser).

As for rendering quality - check our guide here - https://docs.chaos.com/display/PHX4M...ering+In-Depth

Hope this helps

[KushKush]

Hey,

I'm aware of light type and direction difference, I've done test with similar angle and the result was not satisfying, my intent was to illustrate rendering quality and Smoke shape in general compared to scanline. I've managed somewhat improve the shape with reducing smoke opacity between values 0-1 (not 150).
I've made a test with vray sun as you suggested, to strengthen shadows but result is still not as good.
I'd appreciate if Chaos Group can make in depth guide on how to use VrayVolumeGrid, on Vray Channel.

[Joelaff]

Try a constant smoke color rather basing the color off the smoke channel...

Never actually tried rendering in Scanline, but you can definitely get spectacular results render with Vray.

[KushKush]

Try a constant smoke color rather basing the color off the smoke channel...

Never actually tried rendering in Scanline, but you can definitely get spectacular results render with Vray.

In my current tests I use Constant color, problem with constant color though, is that it removes the shadows for some reason.

[KushKush]

Hey,

https://easyupload.io/3svpy9 Here is a single frame VDB(the one in original picture), in case you like to test it. Take a look, maybe you can make it look similar to the example in scanline.
This VDB contains following channels:
Fuel, Smoke, Temperature and Velocity.

[Joelaff]

Hmmm. Shadows internal to the volume, or cast shadows? I still get both shadows here.

[Joelaff]

Here is your VDB. I used the FumeFX preset when importing (changes some values in the volumetric options). I also increased the quality (lowered step sizes, lowered the minimum visible opacity), and use an Area Image filter (default is too sharp for my eye). I lowered the simple smoke opacity. This is a Vray sun with the environment added (hence the color shift).


Max 2021 Vray 6 hotfix 2 file: VDBTest.7z

[KushKush]

Here is your VDB. I used the FumeFX preset when importing (changes some values in the volumetric options. I also increased the quality (lowered step sizes, lowered the minimum visible opacity), and use an Area Image filter (default is too sharp for my eye). I lowered the simple smoke opacity. This is a Vray sun with the environment added (hence the color shift).


Max 2021 Vray 6 hotfix 2 file: VDBTest.7z

Hi, it looks good, better than what I manged to get with volume grid. Thanks for providing the file, I'll try to figure out where was the issue.