From: broehl@sunee.waterloo.edu (Bernie Roehl)
Subject: Re: TECH: More on object collisions
Date: Mon, 2 Mar 1992 22:20:54 GMT
Message-ID: <1992Mar2.222054.2561@sunee.waterloo.edu>
Organization: University of Waterloo


In article <1992Feb26.003339.28432@watserv1.waterloo.edu> dstamp@watserv1.waterloo.edu (Dave Stampe-Psy+Eng) writes:

>Let's assume you do define figures with mathematical functions: some
>sort of CSG using spheres or more complex figures (such as ThingWorld).
>[...]
>But then we must start to work
>with graphics in terms of 3D shapes rather than polygons etc.

This all harks back to some observations I made several months ago, to the
effect that any object we introduce into VR should begin life as a CSG
description.  This has the advantage that you can polygonalize it to any
desired degree of detail (or even make several polygonal versions of an
object available, tuned to the speed of your renderer).

You can also do mass-properties calculations, which can be used to model
object dynamics more accurately.

You can also take "snapshots" in VR and have them rendered (not necessarily
in real time) by raytracing packages to produce nice pictures you can show
to people in the physical world. 

In the context of the current discussion, a CSG representation also simplifies
the collision problem considerably.

> And some tasks will be daunting:  fitting CSG shapes to a human jointed form 
> with natural skin contours, etc.

I suspect this can be done, but have to think about it a bit.  I'm reminded
of the "soft objects" work done by the computer graphics community a while
back; the idea is that you would use an "equipotential surface" to represent
an object.  Mathematically, many operations are simple and the results can
be quite "lifelike".  I'd have to catch up on my reading in this area to say
for sure, though.


-- 
	Bernie Roehl, University of Waterloo Electrical Engineering Dept
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