Better Scattering

I devoted some time today to reading PBR and using the information therein to improve my understanding of volumetric scattering.  The result is that I now have much better-looking gas.  The scattering in this image is pretty much representative of what I'd like to see in the final image with the mining beam, although I'd also like the final gas to be non-homogeneous.

Not surprisingly, the gas increases the variance (although I didn't give the above image very long to render anyway).  The performance hit is not so bad compared to the hit incurred by large scenes. It's clear that my primary optimization target should be scene traversal/acceleration structures.  Tomorrow I will try to implement kD trees and the ropes++ traversal algorithm described here: https://www.gprt.ufpe.br/grvm/Publication/FullPapers/2009/SBACPAD2009_Santosetal.pdf

Oh, and if you take a median filter...I guess it looks kind of good :P