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From: upl@puff.UUCP
Newsgroups: comp.graphics,comp.ai
Subject: Re: Solid Modeling
Message-ID: <592@puff.WISC.EDU>
Date: Mon, 30-Mar-87 14:52:10 EST
Article-I.D.: puff.592
Posted: Mon Mar 30 14:52:10 1987
Date-Received: Wed, 1-Apr-87 01:32:55 EST
References: <798@ssc-bee.ssc-vax.UUCP>
Reply-To: upl@puff.WISC.EDU (Future Unix Gurus)
Organization: U of Wisconsin CS Dept
Lines: 52
Keywords: 3D Graphics, Robotics, Automation
Xref: utgpu comp.graphics:423 comp.ai:345

In article <798@ssc-bee.ssc-vax.UUCP> thornton@ssc-vax.UUCP (Ken Thornton) writes:
>
>
>Unfortunately, there is no CAD/CAM, Robotics, or Automation newsgroups
>so I decided to post here.
>
>I am interested in hearing from people who know about solid modeling systems
>and have experience using them. Specific questions I'm interested in are:

I am doing a solid modeling based animation system as my senior's thesis
(on the Amiga1000. I also hope to eventually release it as a product, it
should beat the living daylights out of Caligari. (Modesty is not one of my
strong points)). In preperation for the thesis, I have spent the past year
and a half researching pertinient issues such as solid modeling techniques.
While I am not as informed as someone might be who has been working in the
field in the real world (i.e. not a student) I have learned a fair bit.
I am also VERY interested in discussing this topic with ANYONE out there!

>
>What is generally preferred, constructive solid geometry (CSG) representations
>or boundary represesentations (B-rep)?

The current trend seems to be toward CSG-BREP hybrid systems. BREP is very
good for generating wireframes, doing things like mass calculations, and
certain approaches to ray tracing. The big problem with BREP is the user
interface. We do not have a true 3d output device available yet, and
most of the systems for plotting 3d points on 2d displays are awkward,
confusing, and time consuming. BREP offers a system in which the user
can work with 3d primatives to begin with, on a more higher level and in
a manner more natural to most people. What most of the systems I've seen
do is take input as CSG from the user, and simultaneously perform 
CSG operations on pre-defined BREP primatives that approximate the CSG
ones. There is a good article in the conference proceedings from
Siggraph '86 on one way to do these CSG ops on BREP objects.
>
>Of the available commercial systems, is CSG or B-rep more predominant?
>
See the above. Realize that I have seen more art intended systems than
CAD type systems, but they seem to be the same difference.

>
>More than anything, I'm interested in stimulating some discussion about 
>solid modeling and related computer graphics algorithms. If such a
>discussion is considered inappropriate to this newsgroup, I might be interested
>in forming another group or starting a mailing list, if anyone is
>interested.

GREAT! Lets discuss!

Jeff Kesselman
ihnp4!uwvax!puff!uhura!captain
(Captain @ Uhura in the Undergraduate Project Lab)