Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!granite!jmd
From: jmd@granite.dec.com (John Danskin)
Newsgroups: comp.graphics
Subject: Re: Defining a sphere with Bezier patches
Message-ID: <209@granite.dec.com>
Date: 29 Mar 88 18:23:35 GMT
References: <2390@saturn.ucsc.edu> <1632@pixar.UUCP> <1639@pixar.UUCP> <3150@csli.STANFORD.EDU>
Reply-To: jmd@granite.UUCP (John Danskin)
Organization: DEC Workstation Systems Engineering
Lines: 31
Keywords: sphere, Bezier, REYES

In article <3150@csli.STANFORD.EDU> rustcat@csli.UUCP (Vallury Prabhakar) writes:
>
>It seems to me that using Bezier patches to generate a spherical surface
>is a rather inefficient method.  A sphere can easily be generated as a
>surface of revolution.  Simply rotate a circular arc about an axis.  The
>arc itself can be generated using Bezier or any other parametric cubic
>approximation. I think Michael Mortenson discusses this in his book
>"Geometric Modelling".
>
>						-- Vallury Prabhakar
>						-- rustcat@cnc-sun.stanford.edu


Ah, but what if your modeler only supports Beziers? And, what do you mean
by more efficient?

	o	Takes up less space
	o	Easier to do ray surface intersections
	o	Easier to tesselate into polygons on the fly
	o	Better numerical characteristics
	o	Bounding box generations on subsets of the sphere are easier
	o	Your sphere modeler needs less total code space


Since you don't win on all of these measures, your posting would be more
helpful if you were more specific.
-- 
John Danskin				| decwrl!jmd
DEC Workstation Systems Engineering	| (415)853-6724 
100 Hamilton Avenue			| My comments are my own.
Palo Alto, CA  94306			| I do not speak for DEC.