clipka <nomail@nomail> wrote:
> - The algorithm described by Ward et al. is NOT radiosity either.

  The problem is that there are two things which have the name "radiosity":

1) By far the most widely accepted definition of the word "radiosity" in the
computer graphics industry and community is to refer to a very specific
algorithm, which is used to achieve diffuse inter-reflection of light between
surfaces. This algorithm is heavily based on using lightmaps, and usually
can only be feasibly implemented in a scanline renderer.

2) A much less widely used meaning is to use "radiosity" as the generic term
for any diffuse light inter-reflection algorithm. In POV-Ray the term is used
in this second meaning. However, most commonly in the computer graphics
industry the term "global illumination" is used instead. (Although GI can
refer to more complex lighting than simply *diffuse* inter-reflection.)

  A much more accurate name for Ward's algorithm (a variation of which is
used in POV-Ray) is "stochastic global illumination method" (or alternatively
"monte-carlo global illumination method", although I'm not 100% sure if
it really *is* monte-carlo sampling technically). However, people use
"radiosity" for historical reasons, because it's short, and because the
documentation uses it (and because it's the SDL keyword). The documenation
and the SDL keyword are technically wrong, but I suppose there's little
that can be done about that. (Although with a full rewrite perhaps a name
change could be fitting.)

> - The algorithm used by POV-Ray DOES come very close to that described by Ward
> et al.; there are a few differences, but none that would justify a complete
> rewrite. The core of the implementation is plain Ward et al.

> So I guess most people complaining that Radiosity works much better in other
> programs than in POV, and then maintain that it should be re-implemented
> according to Ward et al.'s paper, haven't read the paper themselves (or have no
> idea whatsoever about the internal workings of POV's implementation).

  In that case it would be interesting to know why it seems that Radiance
gets superb-looking, accurate and smooth radiosity with (apparently) no or
minimal tweaking, while in POV-Ray it seems to be a constant struggle to
get artifact-free radiosity which looks good and realistic.

  I have the impression that Radiance does something which POV-Ray doesn't
(or the other way around).

> For all those who still ask for TRUE Radiosity to be implemented in POV, I can
> give you one clear statement:

>     This will never happen.

  What do you mean by "TRUE Radiosity"? If you are referring to the
lightmapping precalculation technique, the only limitation to implementing
it in POV-Ray would be that it's more or less limited to polygons. It could
be conceivably be implemented in POV-Ray, assuming it's limited to work with
meshes only (for both the illuminated surfaces and surfaces which illuminate
other surfaces). Given how widely used meshes are, it wouldn't be all that
far-fetched to think that it could be useful even with this limitation.

-- 
                                                          - Warp

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