One of the issues our group has been dealing with since we established our concept is the pipeline of our project, specifically the clouds. While experimenting with cloud shapes, we also tested different rendering software. Ultimately, we decided on Arnold. Next, we needed to determine if we were using Arnold for Maya or Houdini. Initially, we planned to use our lighting artist's rig that she built in Maya in Houdini, and refine from there, but due to some issues with getting HtoA properly installed for both her computer and mine, we were forced to use Maya for the bulk of the lighting and rendering. Because of this, we needed to figure out an efficient way to transfer the cloud volume data (.vdbs) to Maya. One of our Mill mentors, Ciaran Moloney, suggested we use .ass files as a way to transfer the specific Arnold data from Houdini to be read by Maya.

Journey with the .ass File

While we were excited about this option, we ran into numerous problems trying to get them to work and transfer properly. Since we were linking to .vdb files, the files needed to be moved to the Maya project folder. However, the path in the .ass file is linked to wherever the .vdb is located on the exporter's computer, which means it would only be usable on the original user's computer, or the path would have to be edited directly.

Since the path was different for everyone, and we're going to be using several vdbs that will each need repathing, it was impractical to expect everyone to change each individual path. Not only that, but the path needs to be changed for use on our renderfarm as well. To remedy this, I wrote a python script that would repath each .vdb file to the local path of whoever runs the script. So long as the .ass file is in the data subfolder of the Maya and the .vdbs are in the assets subfolder, the script will make a new .ass folder that is localized for your computer. You can also specify which Maya project and .ass file to repath. The PDF guide can be found here:

Another issue we ran into was that our volumes in MtoA weren't interacting with our lights, so there were no shadows.

It turns out that the standard_volume shader in HtoA wouldn't convert properly to MtoA, so we needed to export without the shader, and make one in Maya.

The Final Result

As of right now, we are still organizing and working through some smaller issues that pop up, but we have got a cloud pipeline planned out now.

• Camera and blocked-out geometry exported from Maya to Houdini as .abc files

• Joonho and I create clouds in Houdini

• Joonho exports the scenes as .ass files (my HtoA is broken)

• Bua lights and textures the scene in Maya. The .ass file is imported and localized by the .py script. The volume shader is tested back and forth between us and Bua

• Rendered using Arnold in Maya

• Matte painting and compositing done in Nuke by Jake

Hopefully this workflow is successful!