VolumeGrid Extra Attributes

[vfx_film_televsion]

Hi,

i just found some Extra Attributes on the VolumeGrid in Maya and I'm wanted to know what they do because I couldn't find anything in the docs.



Just looking to optimize render times of VolumeGrids even more....

Kind Regards
Pirmin

[Svetlin.Nikolov]

Hey,

These are hidden attributes that are okay by default so we've left them only for advanced use:

- "Transparency meaning" interprets the transparency/opacity curve either way.
- "Exit level" controls the opacity above which rays stop tracing the volume - you can reduce this, but it might cause artifacts.
- "Skip level" controls the opacity below which rays will not even try to sample the volume - again, you can increase this, but it might cause artifacts.
- "The base density scale" - this is a transparency multiplier that determines how dense the object renders - basically the same as the Simple smoke opacity option, but allows the opacity to remain the same when changing the resolution during Phoenix resimulation, for example.

However, there are other settings that should be way more helpful in speeding the rendering up. How does your setup look and what are your current settings? Do you use probabilistic volumetrics? Also, what lights do you have in the scene?

Cheers!

[vfx_film_televsion]

Hi,

my scene contains like 4000 of these small vdb's (there are 7 different ones with each of them being big from 6 mb up to 90 mb). The seven basic VolumeGrid shapes are then instanced (to a total number of about 4000). I scale most of them up to get the right size, depends on the original size of the vdb but it ranges from a scale factor of 10 to 35. I use probabilistic rendering and changed the Sampler Type to box, in the docs it is described as the fastest one. My smoke Color is based on the channel smoke, and I don't use Light Cache because the voxel I render are smaller then a pixel. Master multiplier is set to 0.5 because of the bright sun. Smoke opacity is also driven by the smoke channel. Optimize Big Volumetric Grids is off because of the amount of vdb's. Input scale in the Smoke Opacity section differs from 5-8 to get a nice looking cloud.
For GI... I switched to Light Cache because its faster. Subdivs to 5000, World Scale check and I render a Fly-Through so I can save the Light Cache Map. Probabilistic Volumetrics Samples are set to 5, the vdb is dense but with less there is a little too much noise on them.
I don't know if the Image Sampler can cause a slow down on a Maya Render Layer with just Volumetric Grids in it so I keep the threshold very high. But in some scenes I combine the VDB's with a intersecting Bounding Box and plug a EnvironmentFog and a Noise texture in to fill up some gaps inbetween the clouds. In those scenes I have to set a threshold of 0.100 so the Fog doesn't render forever. As Post Processing we use Davinci to denoise the images.

Light Setup: Just a Vray Sun and Sky

Don't get me wrong on my first post, VRay renders fast, very fast. It's just, every minute I can save on a shot that renders 1 hour per frame (380 frames) is a blessing.

[vfx_film_televsion]

[Svetlin.Nikolov]

Nice, looks very well set up indeed! Only thing I can suggest is increasing the Step and Shadow Step parameters - especially if your voxels are smaller than a pixel, then you can get away with this, or you can gain at least a little bit of speed by setting Step to 90-95, and Shadow Step to about 300.

Actually there's one more thing eventually - if you haven't already experimented with the Num GI prob. samples option, you could run some tests with it as well - too few samples will make rendering slower, and too much samples will make it slower as well, so you need to find the optimal value in the middle. E.g. if you set it to 2 and to 4 and it's slower than 3, then 3 would be the best setting

Hope this helps squeeze a few more seconds, cheers!

[vfx_film_televsion]

ohh I didn't know that the Step parameters do have an impact when rendering with probabilistic mode on, the same with the GI prob. Samples. I will try this, thanks a lot!

[smbell]

Hey,

These are hidden attributes that are okay by default so we've left them only for advanced use:

- "Transparency meaning" interprets the transparency/opacity curve either way.
- "Exit level" controls the opacity above which rays stop tracing the volume - you can reduce this, but it might cause artifacts.
- "Skip level" controls the opacity below which rays will not even try to sample the volume - again, you can increase this, but it might cause artifacts.
- "The base density scale" - this is a transparency multiplier that determines how dense the object renders - basically the same as the Simple smoke opacity option, but allows the opacity to remain the same when changing the resolution during Phoenix resimulation, for example.

However, there are other settings that should be way more helpful in speeding the rendering up. How does your setup look and what are your current settings? Do you use probabilistic volumetrics? Also, what lights do you have in the scene?

Cheers!

Oh man, I know this is an old thread, but I was able to shave more than 50% off of our 360 clouds renders by taking the Tr Exit Sh Level to 0.950 and the Tr Skip Sh Level to 0.050 with no artifacts or noticable ( to anyone else ) difference in the image. This is going to literally save us days of rendering on this project!!!