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From: amamaral@elrond.CalComp.COM (Alan Amaral)
Newsgroups: comp.graphics
Subject: Re: Ray tracing and caustics.
Message-ID: <1038@elrond.CalComp.COM>
Date: Mon, 13-Jul-87 10:06:11 EDT
Article-I.D.: elrond.1038
Posted: Mon Jul 13 10:06:11 1987
Date-Received: Tue, 14-Jul-87 03:47:22 EDT
References: <219@sugar.UUCP>
Organization: Calcomp, A Lockheed Company, Hudson, NH, USA
Lines: 25
Keywords: ray-tracing caustics algorithm reality


In my last posting I might have given the mistaken impression that the
rendering equation does reverse ray tracing.  This is not the case.  It
works using distributed ray tracing techniques, but instead of creating
a ray tree consisting of refracted, AND reflected, AND other rays it ONLY
picks one ray to follow using monte carlo techniques.  Also, instead of
picking very few initial rays and relying on many second, third, forth,
etc. generation rays (it is interesting to note that they really
contribute much less to the pixel than do the first generation rays)
it picks a larger number (i.e. ~40) of first generation rays distributed
properly.

By the way, it's not obvious, but caustics basically fall out of this
automatically because as a ray hits an object another ray is generated
(randomly, direction based on the reflectivity of the intersected object)
and if the intersection point is close to another object (a transparent
sphere for example), it will intersect the sphere some of the time,
thus picking up illumination from it.  This also happens with objects
that are not transparent, and this mimics radiosity results closely.

-- 
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