How do you volumetric?

[prisonbread]

Hey folks,

Every time I try to employ volumetrics in Octane I give up and move onto something else. I can no longer keep ignoring this feature, though. After a dozen or so attempts and hours of reading/watching tutorials on octane volumetrics, I am convinced that scattering/absorption is the least intuitive aspect of this powerful renderer. Like why is there a thickness and a density slider? Some tutorials on brograph show settings like scale, that seem to be just what I'm looking for, but for some reason do not exist in the later builds. I have tried every combination of parameter from render settings down to absorption , phase, density, and volume step length. Nothing I try achieves the one thing I am going for, the main reason anyone would use volumetrics: volumetric shadows. I'm talking about those gorgeous rays of absent light caused by gobos, branches, or anything between the light source and the floor. I have included a scene that demonstrates the problems I am having. The attached images demonstrate my failure achieving the desired effect with both a fog volume and with a sky object medium. You can see I am getting a nice bit of atmospheric depth in the image where I have used the fog volume, but no rays for some reason.

Please could somebody just open my project, make whatever adjustments are needed to produce the rays of shadow and then tell me what they adjusted exactly and why. If you are feeling super generous you can solve the issue in sky-based fog volume as well, but for now I would be satisfied just to know how to get what I'm going after with a scaleable fog volume.

Before you suggest it, yes, I have downloaded and examined the scenes in Ahmet's sample pack, like the graveyard with daylight and volumetrics, but no amount of scrutiny is helping me understand which settings are doing what. I understand this topic has been beaten to death, and that there are SO many posts about it and cries for it to be demystified (no pun intended), but nothing I have read or watched has corroborated any single, dependable, approach to setting up volumetrics for predictable results. The sheer number of posts out there asking for help with this feature is evidence to me that the concept is too difficult to educate users on by just linking example scenes. We need a real discussion about these sliders!

Thanks for your time,

Ben Matthews

[bepeg4d]

Hi Ben,
I have opened your file, disable the Volume, and re-enable the Environment node with correct settings:

volumetric_test_envMedium.zip

(77.25 KiB) Downloaded 289 times

The Medium radius value is very important, works in meters, and need to be set in relation with the dimensions of the scene, in your case, 5m are more than enough.
Then you need a very low Density value under 1, to simulate the foggy air.
Finally white absorption, and scattering, and a bit of Phase value to enhance the scattering effect in the direction of light.
The dimension and power of the light is also important, I have added an IES file to better concentrate the light in one direction.
Happy Foggy Rendering,
ciao beppe

[Kretschi]

I am also fighting with the fog in Octane. (other renderers such as Redshift even Cinema's Physical are much easier to set up...)
Can't get it right especially for large outdoor scenes where I just want a bit of haze in the background...
Which slider is the Medium radius?

Thanks, Andreas.

[RJMEngineering]

Have to say, this is something that is really playing with me too. There are a few aspects that I think need the help updating. Don't get me wrong, I'm little more than a basic user, but the intuitiveness on some of these features is difficult to grasp.

[prisonbread]

Beppe,

Thank you so much for your time. I have been able to apply these parameters from the scene you adjusted to a number of other projects with great success. I don't fully understand about the medium radius, but I am happy to have a functioning volumetric sky!

Best,

Ben

[prisonbread]

To anyone still trying to wrap their heads around Volumetric lighting:

I came across a tutorial that explains subsurface scattering really well, and moreover, it explains the influence of absorption, scattering, and density REALLY well. I know this conversation started about volumetrics, but I've found that a lot of the theory on absorption and scattering mediums apply to volumetric rendering in general. This tutorial by Rafael Rau helped my SSS and Volumetric game immensely.

https://vimeo.com/234034058

Please check it out!

-Ben