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From: ZeroBlue
Subject: Correct model?
Date: 24 Aug 2000 18:04:51
Message: <39a59c03@news.povray.org>
Does Povray offer the correct model of light, intersecting a transparent
surface, where it divides into one refracted beam and one reflected beam,
whose strenght are varied depending on the incoming angle?

If this is an available feature, how do I set "correct" values? ie.
realworld values for different materials.

/R


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From: Chris Huff
Subject: Re: Correct model?
Date: 24 Aug 2000 18:25:05
Message: <chrishuff-0CD763.17263024082000@news.povray.org>
In article <39a59c03@news.povray.org>, "ZeroBlue" <zer### [at] swipnetse> 
wrote:

> Does Povray offer the correct model of light, intersecting a transparent
> surface, where it divides into one refracted beam and one reflected beam,
> whose strenght are varied depending on the incoming angle?
> 
> If this is an available feature, how do I set "correct" values? ie.
> realworld values for different materials.

It depends on what you mean by "correct"...there is no such thing as a 
perfect simulation of light. POV does not simulate polarization, 
interference, diffraction, etc. When it hits an object which is partly 
transparent and partly reflective, it traces a reflective ray and a 
refracted ray, whose directions and intensities depend on the 
characteristics of the texture at the intersection point.

If you are asking about angle-dependant reflection: standard POV does 
not support this (yet), but MegaPOV, an unofficial version, does include 
it. MegaPOV is available here: http://nathan.kopp.com/patched.htm
The documentation covers this feature, you should read it for an 
explanation of the new reflection features.

POV-Ray 3.5 (which should be released sometime this year) will support 
many of the new MegaPOV features, possibly including angle-dependant 
reflection.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><


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From: Pabs
Subject: Re: Correct model?
Date: 25 Aug 2000 00:03:49
Message: <39A5F03A.2F1C4E74@hotmail.com>
ZeroBlue wrote:

> Does Povray offer the correct model of light, intersecting a transparent
> surface, where it divides into one refracted beam and one reflected beam,
> whose strenght are varied depending on the incoming angle?

You seem to be talking about forwards ray-tracing where rays act just like
streams of photons.
POV-Ray does reverse/backwards ray-tracing where since you are only
interested in light that hits the camera you trace the path of light hitting
the cameras back to its origin so that you may determine the colour of the
ray as it hits the camera.

--
Bye
Pabs


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From: Sigmund Kyrre Aas
Subject: Re: Correct model?
Date: 25 Aug 2000 07:30:04
Message: <39A65890.4D3CFAC4@kyrre.net>
ZeroBlue wrote:
> 
> Does Povray offer the correct model of light, intersecting a transparent
> surface, where it divides into one refracted beam and one reflected beam,
> whose strenght are varied depending on the incoming angle?


reflection_type 1 in MegaPov does this (if I understand you correctly) An
incoming ray will then be reflected if its incident angle is steep enough,
determined by the material's IOR.

sig
--
ICQ 74734588


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From: Sigmund Kyrre Aas
Subject: Re: Correct model?
Date: 25 Aug 2000 07:46:02
Message: <39A65C4E.EA94C418@kyrre.net>
Sigmund Kyrre Aas wrote:
> incoming ray will then be reflected if its incident angle is steep enough,

Eh, the opposite of steep of course :) (Narrow? Shallow?)

--
ICQ 74734588


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From: Chris Huff
Subject: Re: Correct model?
Date: 25 Aug 2000 10:57:51
Message: <chrishuff-87510A.09591825082000@news.povray.org>
In article <39A5F03A.2F1C4E74@hotmail.com>, Pabs <pab### [at] hotmailcom> 
wrote:

> You seem to be talking about forwards ray-tracing where rays act just 
> like streams of photons.
> POV-Ray does reverse/backwards ray-tracing where since you are only 
> interested in light that hits the camera you trace the path of light 
> hitting the cameras back to its origin so that you may determine the 
> colour of the ray as it hits the camera.

However, there is a POV-Ray patch by Nathan Kopp which does photon 
mapping, which is a sort of forward ray tracing: some of the 
illumination is calculated by tracing photons through the scene from the 
light sources, so it can do refractive and reflective caustics, but 
rendering the actual scene is done as it is now. This patch is available 
in MegaPOV: http://nathan.kopp.com/patched.htm
There are a couple small bugs(cylinder lights don't work as expected, 
for example), but it works very well and is reasonably fast.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><


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