POV-Ray: Newsgroups: povray.beta-test: sslt and ior

POV-Ray : Newsgroups : povray.beta-test : sslt and ior		Server Time 22 Dec 2024 20:28:33 EST (-0500)

From: Jim Holsenback
Subject: sslt and ior
Date: 18 Feb 2011 05:09:10
Message: <4d5e4546$1@news.povray.org>

ok, so i've been following sslt threads and was wondering why i get:

povray: render/trace.cpp:3525: void
pov::Trace::ComputeDiffuseContribution(const pov::Intersection&, const
pov::Vector3d&, const pov::Vector3d&, const pov::Vector3d&, const
pov::Vector3d&, double&, double, double, double): Assertion `(sd >= 0.0)
&& (sd <= 1.7976931348623157e+308)' failed.

when i have ior > 3.85 (3.85 works but not 3.86) is this and
unreasonable setting ... btw: was just experimenting and discovered this
accidentally (typo with decimal place) then I narrowed in on the fail
threshold

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From: clipka
Subject: Re: sslt and ior
Date: 18 Feb 2011 07:15:58
Message: <4d5e62fe@news.povray.org>

Am 18.02.2011 11:09, schrieb Jim Holsenback:
> ok, so i've been following sslt threads and was wondering why i get:
>
> povray: render/trace.cpp:3525: void
> pov::Trace::ComputeDiffuseContribution(const pov::Intersection&, const
> pov::Vector3d&, const pov::Vector3d&, const pov::Vector3d&, const
> pov::Vector3d&, double&, double, double, double): Assertion `(sd>= 0.0)
> &&  (sd<= 1.7976931348623157e+308)' failed.
>
> when i have ior>  3.85 (3.85 works but not 3.86) is this and
> unreasonable setting ... btw: was just experimenting and discovered this
> accidentally (typo with decimal place) then I narrowed in on the fail
> threshold

That's a problem with a certain approximation used inside SSLT, which 
goes bonkers at high refractive indices (and also at refractive indices 
<1.0), claiming that at a refractive index of 3.86 or above you get an 
average internal reflectance of >100% (or <0% if the ior is <1.0). I 
noticed this too yesterday, and right now I'm digging for a suitable 
replacement formula, for this and other reasons.

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