> Can anyone comment about global illumination in POVRay?

Well, the principle is very simple: All objects cast shadows, as you know.
But they also reflect light, when you turn on radiosity. This is the same
term as global illumination. You need it, to obtain a natural spread of
light. The reflections from radiosity are just not mirror-like. They are
diffuse. It's the same effect that happens when light enters from a window.
The walls reflect that light, in very diffuse directions. That's why you
don't see a clear reflection on the wall. Unlike a mirror, it's a diffuse
reflection.

The documentation for POV-Ray is very informative, I hope you'll read it. I
also recommend that you load the include-file "rad_def.inc" into the editor.
All parameters are setup and ready to use. You can choose between different
qualities of radiosity. They are simple to use. You just do as I did, in the
example I posted yesterday... When radiosity is turned on, light will bounce
off all objects, at least once. You can adjust the light to bounce off
twice, or more times if necessary (that is rare).

The sky_sphere is also an object, but unlike most objects, the sky_sphere
emits light. It's not a "light_source" but on the other hand, it doesn't
NEED a "light_source" to ... light.. Perhaps this sounds a bit strange, but
the point is: An object can either absorb light, or emit light. In both
cases, radiosity makes the light travel to nearby objects. Any object can
emit light of course, not just the sky_sphere. To make an object emit light,
you raise the "ambient" value in the object's finish statement. Like this:

sphere { 0, 1 pigment { rgb 1 } finish { ambient 1 } }

If you don't want the object to emit light, set ambient to 0.. Please note
that you can set the ambient value higher than 1 if necessary... Maybe you
ask yourself: If objects can emit light, why have light_sources?  They're
not needed.  That's true, and you can make a beautiful scene without any
light_sources, just with pure radiosity. This would be the most realistic
approch. But in many cases, it's too slow if you want good quality. That's
why we mix radiosity with ordinary light_sources.. These light_sources rely
on a completely other formula, and are independant of radiosity. But they
have some advantages, such as clear defined shadows, and nice specular
highlights on objects.. The trick is then to balance the two formulas
(radiosity and light_source) to get realistic results.

But it's possible... And OH, I have to stop writing now.. I have work to do.

Regards,
Hugo

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