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From: pearce@calgary.UUCP (Andrew Pearce)
Newsgroups: net.graphics
Subject: Re: Wave-front ray tracing?
Message-ID: <228@vaxb.calgary.UUCP>
Date: Tue, 4-Mar-86 15:02:31 EST
Article-I.D.: vaxb.228
Posted: Tue Mar  4 15:02:31 1986
Date-Received: Thu, 6-Mar-86 05:43:55 EST
References: <13300001@ccvaxa>
Organization: U. of Calgary, Calgary, Ab.
Lines: 41
Summary: pointer to papers on "wave-front" ray tracing

In article <13300001@ccvaxa>, aglew@ccvaxa.UUCP writes:
...
> Query: might not wave-front type computations be more efficient? Take a
> wave-front from your light source (spherical, cylindrical, or planar)
> start it propagating, and compute its first intersection with an object.
> Parts of the wave-front will be modified - light "densities" will be changing
> all the time.
...
> Has this been tried as an alternative to ray-tracing? Any references?
> Any overwhelming reasons why it won't work? The only thing I can see is that
> it is hard to work backwards from eye to light source.

Yes, this has been thought of and versions have been implemented.  The two
that come to mind right away are :

J. Amanatides, "Ray Tracing with Cones", ACM SIGGRAPH, Vol. 18, No. 3, 1984,
	pp. 129-136

P. Heckbert and P. Hanrahan, "Beam Tracing Polygonal Objects", ACM SIGGRAPH,
	Vol. 18, No. 3, 1984, pp. 119-128

They use the "wave-front" idea and break the wave into sub-waves when an object
is hit.  It all works fine, and samples texture maps *very* accurately even at
extreme angles or distances, but problems crop up when the beam or cone has
to be refracted through an object.

This critisism is more valid of beam tracing than of cone tracing, cone tracing
is more an alternative to super-sampling for anti-aliasing and to avoid the
granularity of regular ray-tracing for small objects at great distances from
the viewpoint.

Some work is also being done on using this type of idea for simulating and
testing room accoustics (using multiple sound wave fronts rather than light).
I think this is being done at the U of British Columbia.

Andrew Pearce   Dept. Computer Science
U of Calgary    2500 University Dr.
Calgary,	Alberta, Canada
T2N 1N4

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