Over the last two years, there has been an ongoing effort led by Sam Skillman to refactor the volume rendering (VR) code for making volumetric images using radiative transfer models on simulation outputs.  Because it's such a large functional change to the codebase, all of these commits have been kept in the `experimental` head on the dev branch of yt up until now.  A month ago, there was a code sprint at SLAC where Matt, Nathan, Suoqing, Andrew, Kacper, Ji-hoon, Sam, and I worked hard in getting the new VR code ready for release to the larger community.  While this code still needs work before it can go into the next stable version of yt (3.3), we've now merged the code into the main development head, and we invite users to try out this functionality to see how well it works for their own datasets.

For a full description of the new volume rendering interface and how to use it, please see the narrative docs, new cookbook recipes, and annotated example.  For more background on where we'd like this functionality to go in the future, see the YTEP.

VR Docs: http://yt-project.org/docs/dev/visualizing/volume_rendering.html

Cookbook (search for Volume Rendering): http://yt-project.org/docs/dev/cookbook/index.html

Annotated Example of VR usage: http://yt-project.org/docs/dev/visualizing/volume_rendering_tutorial.html

VR YTEP: http://ytep.readthedocs.org/en/latest/YTEPs/YTEP-0010.html

To get access to this new VR functionality, you have to be on the development (ie "yt") branch and using the most recent changeset (ie "tip").  For information on how to switch branches, see: http://yt-project.org/docs/dev/installing.html#switching-versions-of-yt-yt-2-x-yt-3-x-stable-and-dev .  If you wish to continue to use the old VR interface, it will remain available in the yt/visualization/volume_rendering/old_camera.py file.  

Thanks to all of the hard work by the developers who helped get this out! 

Cameron