Hello,

I try to use the Pyroshader for cumulus clouds because it has multiple scattering integrated. But I think I must be doing something wrong because it looks the same with or without ‘multiple scattering’ checked in the shader.

What I am doing: create a pyro shader, assign the pyro1 to my geometry, set the smoke density to .6 and the scattering phase to forward (.3). It renders nicely - but much slower than the usual billowysmoke, but thats not the case here.
Then I activate ‘scattering’ in the scattering tab. I choose a stepsize 10 times the volume step size. In my case thats 3. The camera sees the whole volume.
Then I generate the points and check them with a file node to be sure they are generated.
But when rendering no subsurface scattering is visible at all. I tried to use the ‘color correction’ and choose to tint it pure red to see if theres any difference - but there isnt.

best,
sven

Does someone understand my problem? Should I post this into “Technical Discussion”?

Don't know if I can help you but can you post a sample file.

i am not sure if pyro has multiscattering integrated
it seems to me that it only scatters “light” from fire volume through smoke
so if no fire is present then no scattering occurs
I may be wrong though since I don't use pyro, just read the manual (and I didn't find any mention about multiple scattering in pyro)

what you can do to get multiple scattering is render in PBR and increase Volume limit
this should work with any Volume shader but it may be unbearably slow

another thing you can do is use Bake Volume SOP, it doesn't work with actual lights you need to provide position, intensity and light color in SOP and then wait for it to compute, maybe use sample points if it cooks too slow
then render without light affecting that volume since it will have lighting baked in
this however doesn't account for occluding objects so no shadows from external objects will be computed
but can be used for clouds with single point light like the sun

and I have asked this before in this thread
http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=97704#97704 [sidefx.com]
with no answer so I guess not many people have insight on this and I came into conclusion that pyro scattering works only with fire but maybe someone knows some secret?

It's like you say tamte, two pointclouds are created one for the fire and one for the smoke.

SIDEFX DOC
The Pyro material uses the fire point cloud to fill the fire volume with point light sources, with the intensity and color of each light derived from the parameters on the Fire tab. When calculating illumination of the smoke from fire emission, the material will loop over some subset of these fire point lights and accumulate their contribution just as it does for external lights. The amount of illumination contributed by each one of the fire points is subject to the same attenuation factors as the external sources: distance, the smoke’s own density, as well as any occluding objects embedded in the smoke. Each point in the smoke point cloud stores the resulting fire illumination. Then, while marching through the volume to shade it, the material will use a neighborhood of these precomputed fire illumination results, average them together, and use them in the final shading calculation.

Thank you both very much.
I was afraid of an answer like this. thx for the link to your thread tamte.
I guess multiple scattering would be render overkill anyway. I will continue to use the pyroshader because it allows me to use the forward scattering phase which is quite important for clouds.

Well I'm not too unhappy with the look of the cloud color and density at all.
The biggest problem is, in my opinion, the overall same distribution of the noise. I tried to solve that by randomize the noise amplitude for each instance. But what I need is to control a specified group of points. Lets say the bottom points of the cloud. I want to group them so that I can assign a higher amplitude of the noise.

Btw: I use a point cloud and for instancing a cloud sphere onto each point. The idea is based on a file from odforce: http://forums.odforce.net/index.php?/topic/12923-pyroclastic-noise-demystified [forums.odforce.net]

If someone wants to see, heres my file. And also two improved renderings.
Any suggestions are welcome.

sven