"Tim Nikias v2.0" wrote:
> 
> Well, here's the pic I've forgotten to attach...
> Notie that all those artifacts get smoothened
> out later when using a higher error_bound.

This image strongly indicates a not high enough max_trace_level.  For
radiosity with reflection and refraction it is usually advisable to turn
off reflection and refraction for the pretrace.  For this you usually need
three renders:

1) generate photons with correct finishes/interiors 
2) generate radiosity data without reflection and refraction.
3) do the final render using both previously generated data files.

Christoph

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Tim Nikias v2.0 wrote:

> Additionally, it might be of interest to know that using
> actual lightsources gives sharper shadows (though using
> area-lights to get soft shadows is a must for realistic lighting,
> somewhat paradox). BUT, it must be said that shadows
> produced by pure radiosity lighting are VERY soft.

It really depends on the circumstances. With a sufficiently low 
error_bound and high count, and the right environment, I have seen 
radiosity produce some pretty sharp shadows. The "problem" is that the 
scenes where radiosity typically has the greatest obvious impact vs. 
normal point lighting are those where there are large lit areas (skies, 
well-lit rooms with white walls, etc) and naturally when light is coming 
from everywhere, you're going to have some pretty soft shadows.

If you want sharper shadows in such a scene, you'll have to set it up so 
that the "main" light sources in the scene are much brighter than the 
lit objects around them (or else reduce the radiosity brightness, which 
provides much the same effect). I think you'll see this as you start 
playing with outdoor scenes with full sun, although an indoor 
environment could also work if you're using a bright, naked light bulb 
for lighting.

-Xplo

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Well, not much to say to that, you've got straight
A's on your radiosity-examn. :-)

Seriously though: I was just analyzing indoor scenes
with pure radiosity, especially scenes where the lightsource
is more or less a lightbulb or something similiar. Shadows
produced by those are very soft, as said before.
But sure, with the right settings, one could get crisper
shadows. Still, I'd go so far and say that for the majority
of scenes where radiosity is used indoors, shadows
produced thereby are very soft.


-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


>
> > Additionally, it might be of interest to know that using
> > actual lightsources gives sharper shadows (though using
> > area-lights to get soft shadows is a must for realistic lighting,
> > somewhat paradox). BUT, it must be said that shadows
> > produced by pure radiosity lighting are VERY soft.
>
> It really depends on the circumstances. With a sufficiently low
> error_bound and high count, and the right environment, I have seen
> radiosity produce some pretty sharp shadows. The "problem" is that the
> scenes where radiosity typically has the greatest obvious impact vs.
> normal point lighting are those where there are large lit areas (skies,
> well-lit rooms with white walls, etc) and naturally when light is coming
> from everywhere, you're going to have some pretty soft shadows.
>
> If you want sharper shadows in such a scene, you'll have to set it up so
> that the "main" light sources in the scene are much brighter than the
> lit objects around them (or else reduce the radiosity brightness, which
> provides much the same effect). I think you'll see this as you start
> playing with outdoor scenes with full sun, although an indoor
> environment could also work if you're using a bright, naked light bulb
> for lighting.
>
> -Xplo
>


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Tim Nikias v2.0 wrote:
> 
> Seriously though: I was just analyzing indoor scenes
> with pure radiosity, especially scenes where the lightsource
> is more or less a lightbulb or something similiar. Shadows
> produced by those are very soft, as said before.
> But sure, with the right settings, one could get crisper
> shadows. Still, I'd go so far and say that for the majority
> of scenes where radiosity is used indoors, shadows
> produced thereby are very soft.

As they probably should be.

Next time you're in a room with a radiosity-ish light source (say, a 
lamp with a large shade that blocks out most of the direct light) take a 
look at the shadows. My own room is like that, and looking around, even 
objects a dozen feet from the lamp and a few inches from the wall have 
rather soft shadows.

I doubt you have any viable pure radiosity scenes that accurately 
simulate a naked lightbulb in a room; the lightbulb would be so small 
that even with count 1600, the vast majority of those tests would miss 
it entirely, resulting in massive artifacting; increasing recursion to 2 
or 3 (as appropriate for such an environment) would only increase this, 
as would setting error_bound low enough to make the radiosity capable of 
producing sharp shadows (say, .1 or less).

If a method is found and implemented to allow significantly higher count 
values, the naked light scene would make an interesting experiment. 
However, AFAIK, no one is working on it (and I have no ideas).

-Xplo

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On Sun, 13 Jul 2003 11:50:52 +0200, Apache wrote:

> ratiosity will take media into account with "media on". But what about the
> other way around: media taking ambient light sources or diffused light into
> account?

Radiosity depends on 2 dimensional surfaces by nature making it impossible 
(someone prove me wrong!) to render multiple scattering with it. It IS 
possible to render multiple scattering with photons so I stand by my 
opinion that radiosity should be done in and diffuse reflection should be 
calculated using photons.

PS. Hey everyone! It's been a while since my last post but I haven't given 
up. ;-)

-- 
light_source#macro G(E)sphere{z+E*y*5e-3.04rotate-z*E*6pigment{rgbt#end{
20*y-10#local n=162;1}#while(n)#local n=n-.3;G(n)x}}G(-n).7}}#end//GregE

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Greg Edwards wrote:
> 
> Radiosity depends on 2 dimensional surfaces by nature making it impossible
> (someone prove me wrong!) to render multiple scattering with it. It IS
> possible to render multiple scattering with photons so I stand by my
> opinion that radiosity should be done in and diffuse reflection should be
> calculated using photons.

I am not really sure what you are talking about here but i have the
impression that you got something seriously wrong.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 17 Jun. 2003 _____./\/^>_*_<^\/\.______

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On Sat, 26 Jul 2003 13:04:56 +0200, Christoph Hormann wrote:

> 
> 
> Greg Edwards wrote:
>> 
>> Radiosity depends on 2 dimensional surfaces by nature making it impossible
>> (someone prove me wrong!) to render multiple scattering with it. It IS
>> possible to render multiple scattering with photons so I stand by my
>> opinion that radiosity should be done in and diffuse reflection should be
>> calculated using photons.
> 
> I am not really sure what you are talking about here but i have the
> impression that you got something seriously wrong.
> 
> Christoph

What I meant to say was that, by my understanding, the radiosity system is 
incompatible with multiple scattering. I then went on to ramble how I 
believe it should be replaced with photon mapping.

-- 
light_source#macro G(E)sphere{z+E*y*5e-3.04rotate-z*E*6pigment{rgbt#end{
20*y-10#local n=162;1}#while(n)#local n=n-.3;G(n)x}}G(-n).7}}#end//GregE

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Greg Edwards wrote:
> 
> [...]
> 
> What I meant to say was that, by my understanding, the radiosity system is
> incompatible with multiple scattering.

What makes you think this?

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 17 Jun. 2003 _____./\/^>_*_<^\/\.______

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On Sun, 27 Jul 2003 13:38:46 +0200, Christoph Hormann wrote:

> 
> 
> Greg Edwards wrote:
>> 
>> [...]
>> 
>> What I meant to say was that, by my understanding, the radiosity system is
>> incompatible with multiple scattering.
> 
> What makes you think this?
> 
> Christoph

I could easily be mistaken, but AFAIK, radiosity takes only a few samples 
for many pixels (count) to speed up the render process and when finding the 
colour for a given pixel, finds the nearest calculated samples 
(nearest_count) on the same surface and does a weighted average. This is 
kinda hard to do when there are no surfaces (3d media). If I'm wrong, just 
say so and I'll shut up. ;-)

-- 
light_source#macro G(E)sphere{z+E*y*5e-3.04rotate-z*E*6pigment{rgbt#end{
20*y-10#local n=162;1}#while(n)#local n=n-.3;G(n)x}}G(-n).7}}#end//GregE

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Greg Edwards wrote:
> 
> [...]
> 
> I could easily be mistaken, but AFAIK, radiosity takes only a few samples
> for many pixels (count) to speed up the render process and when finding the
> colour for a given pixel, finds the nearest calculated samples
> (nearest_count) on the same surface and does a weighted average. This is
> kinda hard to do when there are no surfaces (3d media). If I'm wrong, just
> say so and I'll shut up. ;-)

Ah, so you don't mean there is a problem for radiosity taking into account
media but media being illuminated by diffuse light.  This is indeed not
handled in POV-Ray radiosity at the moment - it is not impossible to do
this with monte carlo radiosity though.

It all comes down to an effect quite rarely needed (since diffuse light
rarely creates a very clearly defined effect on media) and that would be
quite slow to compute.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 17 Jun. 2003 _____./\/^>_*_<^\/\.______

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