Hello! I’ve been working on this project for months, and I’m happy to finally make it public.
Surface scattering has seen significant advances over the last few decades. We've gone from Cook-Torrence to multiscatter GGX and Disney's Principled shader. Volume scattering has not seen the same progress; it's telling that the primary scattering function we use, the Henyey-Greenstein, is over 60 years old. One possible reason for this is the MERL database, a collection of measured surface reflectances from a wide variety of materials. Easy access to that kind of data helped fuel the study of some of the above bidirectional scattering distribution functions (BSDFs).
Volume scattering could use a similar database. So as a supplement to our paper, we’ve gathered as many volume scattering function (VSF) samples as we can find in one place, in the hope that it triggers the same spark of innovation.
That may not seem useful, on the surface. However, each of those scattering functions has been translated into multiple Open Shading Language shaders. These vary in their level of realism and performance cost, and in my ever-so-slightly biased opinion are a step up from what you normally see for volume rendering. Some of these are “chromatic,” in that they vary the colour associated with each component function to try and approximate colour-based scattering effects. All of it is under an open-source license, of course.
Currently the database is dominated by cloud and fog scattering functions, but we’re hoping to expand it. I’ve started looking into biological scattering functions, for instance. If you’d like to help, you can clone the repository and create a merge request or get in touch with the email address listed in the database.