Hello,

i'm new to this forum and new to Houdini. I'm familiar with Maya and the basics of Maya Fluid. I don't have any specific Houdini question right now. I'm looking into creating clouds and doing research how clouds are being generated for film. I'm interested in the actual workflow. In most papers or interviews people say that they used either a self written in-house tool or a combination of Houdini and Maya. For example:

“The VFX team’s first step was to bring the polygon clouds into Houdini and voxelize them,” http://www.mrxfx.com/press/31 [mrxfx.com]

I read “voxelized them in Houdini” quite often. It seems to be a commong workflow. To understand this correct: Voxelize means that the inside of the mesh will be filled with a specified amount of voxels, depending on your resolution.

Do you think its a common workflow to create clouds for feature films?
Did somebody of you created clouds which were used in a film?

What happens after voxelizing?
The animation is driven through fluid dynamics and force fields?
A voxelshader in combination with a noise is applied to render it?

Sven

basically - yes.

have a look through the volume tools/example files and you'll see that a shape > volume > shaded w/noise etc is a pretty standard way to make clouds…

Hey Sven, at least some big productions use Houdini and mantra for clouds and volumes. I actually have the impression it's becoming a major selling point of Houdini/Mantra for bigger studios.

Mantra is quite fast for rendering volumes.

There are various ways to generate clouds. You can do it completely procedurally or partly modelled. The procedural parts can be both on the sop and shop level, and if you consider it separate, dops. It is also possible to render metaballs as volumes.

There is a lot you can do with volumes, some of it not directly related to actually rendering clouds. For example, they are a fast and robust way to decide if something is inside or outside a geometry and thus useful for collision detection, grouping geometry, and intersections.

Volumes can also hold field data, both as scalar and vector values. So they can be used in simulations and can be super useful (and economic!) to blend and transfer attributes. In a shop context you can even use invisible fields as shading parameters. The pyro shader is a superb example of this.

I love volumes! They are one of the things that make Houdini so great.

But but, I believe some people on this board are way way more experienced than me in clouds and volumes, and they could add a lot more to this topic.

Thank you both for your replies!

@Soothsayer: True, many workflows for clouds in feature films depend heavily on Houdini!

At the beginning of my research I thought that fluid simulations were the most common way to generate clouds. But at this stage it seems that a procedural approach is more often used. I guess fluid simulations take too much computing time and procedurals are more art-directable?

Maybe its not new to the professionals of you, but in this document http://magnuswrenninge.com/content/pubs/VolumetricMethodsInVisualEffects2010.pdf [magnuswrenninge.com] (60mb) from Siggraph 2010 some big vfx companies wrote about their workflow. Fluid simulations are rarely mentioned. The most important technique seems to be “pyroclastic displacement” or “pyroclastic noise”. Google doesnt know much about those topics

But I saw a tutorial from cmiVFX http://www.cmivfx.com/tutorials/view/280/Houdini+Fractals [cmivfx.com]. The technique is called “Custom Volumetric Displacement” but I guess its basically the same?

Levelsets seems to be the second most important thing if you deal with clouds. Are they implemented in Houdini?

Edit: found the solution for levelsets: Levelsets = IsoOffset (outputs a SDF Volume)