View Full Version : Usefulness of caching Radiosity

06-25-2014, 12:22 PM
Hey folks,

I ran into a problem using the cache for Radiosity and in searching the Forum find that it's a fairly old issue (back to 9.6 days). What's happening is that at a certain point, render times increase drastically for each frame as in going from 45 mins per frame to over 8 hours even though there's only subtle changes in the animation and camera position.

At first, I tried just caching a single frame where the animation becomes minimal but I'd left the rest of the settings at their default which means the preprocess was set to automatic. Along with the render times increasing about 1 hour per frame, the cache file size bloated up to 181 Gb! I aborted, cleared the cache and tried again using the Locked option. The cache file remained constant at around 3 Mb, but still had the render times increasing about 1 hour per frame.

In Rebel Hill's Global Illumination Rendering video, he touches on using the cache but didn't mention this issue. Several of his other forum replies on the issue however, he essentially says to NOT use the cache and instead go with a method of high value of rays and secondary rays. This is what I ended up doing. Even so, I still ended up with a bit of GI flicker but fortunately it's not noticeable in the final comp.

What I come away with is that I'll probably never use radiosity again for animation but it got me wondering why/when it would be used. Is there some technique or setting other than trial and error to reliably get this working in a useful manner?

06-25-2014, 02:52 PM
As I understand it render times increase when using the cache because Lightwave writes more information to the cache as it renders each frame. You can bake the radiosity cache first and then lock it. That prevents lightwave from writing any more info to the cache while rendering but then you start the render with a big cache so it is a catch 22. I like to turn off Interpolated on the radiosity tab and take the render hit because I would rather have the computers work an extra day on rendering than spend a day of my time looking for settings that will work. I turn down Rays Per Evaluation till I get render times that I can tolerate. That gets rid of the flickering but adds graininess depending on the RPE setting. I also would like to know how to use interpolated radiosity without spending many hours of trial and error.

06-26-2014, 05:52 AM
Using high rays for interpolated rad and not using cache is the way to go if you're trying to render animation that contains deformations, moving objects, lights, etc. This lets you get a good chunk of the interpolation speed saving, whilst being able to minimise flicker in these situations.

If you're only moving the camera... simply hit "bake scene", let it cache, set the cache to locked, render... done.

Tutorial link in the sig gives expanded detail, variations on workflow, and different ways of approaching things that'll work for some specific situations better than others.