Newsgroups: comp.graphics
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!infonode!genius!matt
From: matt@genius.Berkeley.EDU (new user)
Subject: Re: Ray Tracing Acceleration ... Is non-uniform s
Message-ID: <1991Jun7.190058.23133@infonode.ingr.com>
Sender: usenet@infonode.ingr.com (Usenet Administrator)
Reply-To: matt@genius.Berkeley.EDU (new user)
Organization: Intergraph Corp. Huntsville, AL
References: <1991May14.070444.18261@images.cs.und.ac.za> <1991May31.175154.4496@pixar.com> <1991Jun7.174920.493@otago.ac.nz>
Date: Fri, 7 Jun 1991 19:00:58 GMT


Graham Furniss, PhD student, Graphics Research Lab, University of Otago, writes
|> We have been using a ray-tracer for commercial TV animation for the last
|> 3+ years. This system is a Constructive Solid Geometry (CSG) system which uses
|> ray-tracing for ALL picture output. This includes B&W sketch prototyping and
|> full colour, full texture, full transparency pictures. Three years ago I
|> completed an MSc. which compared our system with two polygon/wire frame
|> systems. For reasonably complex pictures the ray-tracer was orders of magnitude
|> faster! 
|> 

I find this hard to believe.  Are you saying that ray tracing a wire frame image 
was faster than using a line drawing algorithm.  

|> 2). Octree flattening. This takes the adaptive division from 1) and converts it
|> into a regular space division. This allows the use of a fast voxel skipping
|> algorithm. ( John Cleary and Geoff Wyvill )
|> 
This sounds like an interesting idea.  How do turn an octree into uniform space
division without losing the advantages the octree gave in the first place.

|> 3). Edge following. This uses the fact that in any picture each colour will
|> cover more than a few pixels. This means that rays are cast only on the edges
|> of areas of colour; the inside areas can be flood filled without casting extra
|> rays. This has resulted in casting less than %10 of the rays for a full ray
|> trace in some cases. Note that the resulting picture is identical to the fully
|> traced version. ( Geoff Wyvill, Alistair Ward and Tim Brown )
|> 
How do you determine where the color edges are without casting rays?

|> All the techniques used in our system are published, mostly 
|> in CGI proceedings and "The Visual Computer". 

Can you post the specific month and year?

take it easy
Matthew Fisher