Subject: Re: Collision Detection
From: Ernie Wright <[email-masked]>
To: [email-masked]
Date: Mon, 25 Mar 1996 14:50:41 -0800

Dimitri Holman wrote:

> Collision Detection in 3D is non-trivial BUT can be done fast with the
> correct algorithm. Fast as in REAL-TIME. We use it in the Vis-Sim world
> all the time.

Is that why so many of the DIS runs I've seen feature "flying" and "bur-
rowing" tanks?  Real-time 3D surface interaction isn't very robust.

Ted Stethem replied:

>   In 3D, it would be necessary to have X, Y and Z coordinates for the 
> points plus have the capability to interpolate points in-between when 
> intersecting between them, say a line between two sets of coordinate 
> points. I need to dig up my calculus book and go over the section
> about intersecting surfaces again.

It's worse than that.  If your terrain is smoothed or bump mapped, for
example, you have to calculate the interaction based on the continuous
surface implied by the shading, and not the geometry of the underlying
polygons.  And consider a wheel rolling over a peak:  the axis of rota-
tion moves and the wheel rotates, but the point of contact with the
terrain is fixed for a time.

I doubt the calculus book will be much help, since most problems of this
kind are difficult to solve analytically.  Look for books on numerical
methods in physical simulation, in addition to material specific to CG.

- Ernie