I have utterly utterly no idea why, but I had to do strange things to OE to
get this thread to appear! Anyway...

> > Does POV-Ray do *real* radiosity?
>
>   What is "real radiosity"?
>
>   Firstly, the exact meaning of "radiosity" is a specific algorithm where
> lightmaps are calculated projecting (usually with scanline rendering) the
> scene onto each surface of the scene. This algorithm has nothing to do
> with raytracing nor with light sources per se.

...which would render my initial assumption invalid. I clearly don't know
what I'm on about.

>   I suppose that you are using the term "radiosity" as meaning any
> global illumination algorithm. Even so, there's no such a thing as
> a "real" algorithm. There are several different algorithms, but we
> can't say any of them is more "real" than the other. They are all
> approximations, different ways of calculating a similar thing.
>   One algorithm can be "better" than another (by whatever criteria
> you happen to choose), but quality does not make it the "real" algorithm
> (and the other ones "fake").

Quite right.

> > According to my understanding (which may or may not be correct)
"radiosity"
> > algorithms start from the light source(s) and follow the paths of the
rays
> > forwards into the scene, eventually reaching the camera.
>
>   That's just *one* way of doing it. In no way it's the only way, nor
> necessarily the "best" way. And as I already said, there's nothing in
> this algorithm which would make it "real".

As established, my initial assumption was not correct. I assumed there was a
class of programs which do what raytracers do, but in the other direction,
yielding heigher quality images with much larger render times. Apparently
that's not the case at all...

> > However, POV-Ray is
> > "radiosity mode" seems to still follow light backwards, only this time
> > attempting to take diffuse interreflections into account.
>
>   Right. There are good advantages (and perhaps some disadvantages) of
> doing it that way.

OK. That makes sense.

> > Does this really count as radiosity?

Dumb-ass question.

> > Could the
> > photon mapping algorithm be changed to include diffuse elements also?
Would
> > this be worth doing?
>
>   This is a FAQ.
>   Nathan Kopp tried to implement global illumination using photon mapping,
> but AFAIK the results were not very promising.

That's a shame.

>   If you think about the amount of samples needed to calculate global
> illumination for a huge scene, you will understand why this is so.

Yeah, actually... caustics are heigh-detail, but they don't take up such
surface area, so the photon maps don't cover very much. Global lighting
would take too much memory I suppose.

> It's
> very difficult to calculate more samples where they are needed and less
> samples where they aren't. This is an advantage of the stochastic
algorithm
> used by POV-Ray.

Ah well - I guess I'm just trying to get it to solve the wrong sort of
problems.

(Actually, I tried it with a ambient white sky over a matt white floor, with
a green ball in the middle. Didn't take long to find parameters that worked
perfectly. Looked good too.)

Thanks.
Andrew.

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