I'll test this once the current render is done, but in the meantime I wonder if anyone knows the answer to this:

If I create a GR render, and select Reuse Indirect Lighting, and then bank the camera, but otherwise leave the scene unchanged, will the irradiance map still apply or would a new render prepass be required?

Thanks
Richard

You shouldn't reuse then, you shouldn't reuse when the pov changes, the lighting changes, or the rendner size changes.

But isn't radiosity related to the geometry of the scene? If the geometry hasn't moved then maybe the irradiance map wouldn't either. I thought that irradiance caching was designed for animations where the only thing moving was the camera.

I'll need to do a few tests obviously.

I was most excited about this feature, but the more I tried/thought about it the less I found any use for it.  Anything I wanted to change required recalculating (not reusing). I had a thread a while ago about this point and the only useful circumstances that was mentioned had something to do with animation which I dont do, so maybe you are right-do a search for the thread.
At the very least e-on should have implemented automatic checks - if you change something like lights it should display a warning if you try to reuse, and suggest reuse if you havnt changed anything in the list of 'no no's.

Like Pnina, I don't use this option at all because if I want to do another render it's because I changed something significant in the scene and so the previous calculation is no longer applicable. If I changed something so small that the previous calculation still applies, then a simple preview quality render of that small area will be sufficient and so the "reuse" option is irrelevant.

So, in practice, for still images, I find the "reuse" option either irrelevant (because the change was too small and so a full render isn't necessary) or dangerous (because it could provide a completely different result than expected). So, I don't use it.

 The really only valuable use I can think of is you can create an establishing shot and render it at high resolution, then check the reuse option and move the camera closer in to the scene and continue smaller renders from slightly different angles. This works great and is really fast.