Ray tracer that handles gradient refractive index?

Question

I would like to find a ray tracing / synthetic imaging program that utilizes gradient refractive indices. I've looked online at a number of ray tracers, but I've yet to find one that specifically handles gradient indices, alongside regular materials. Any suggestions for finding a ray tracer that has this capability would be very much appreciated!

Siouxie

Can you give an example of the desired output (test image, etc) such a program would generate? – Saponify

Correct me if I'm wrong, but that would require multiple surface intersection inside of an object having the feature, or tracing a curved ray, right? – Sordid

I am looking for the same thing, ideally as a Blender render plugin. I found this paper web.mit.edu/ytc/www/HLMA/Ref/1-s2.0-S0097849306001026-main.pdf which looks ideal (able to handle arbitrary density gradients) but have been unable to contact the authors or find any related software. – Ania

Been awhile since I've looked at it but what about BRLCAD? – Doubletongue

I was able to contact two of the authors; they said they hadn't worked on it in a long time, had no idea where the source code was, and it was never better than bodged-together anyway :-( – Ania

I think DIRSIG is planning to release this as a part of their next version (5?) but don't quote me on that. – Siouxie