Path: chuka.playstation.co.uk!news
From: Developer Support <dev_support@interactive.sony.com>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: Collision Detection in a 3d Environment.
Date: Fri, 13 Jun 1997 09:47:47 +0100
Organization: Sony Computer Entertainment Europe
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colin adams wrote:
> 
> Hello All
> 
> During the course of a Game one of the main functions that the
> Game must perform is Collision Detection. Both -:
> (a). Environment to Characters.
> (b) Character to Character.
> 
> The Documentation I possess regarding this subject is sparse, to put it
> mildly.
> 
> My Questions are-:
> 
> 1. Which Method is Best?
> The  Method I used in my 2d projects was the "Bounding Box algorithm".
> Is this method  applicable to 3d? I have heard of a "Bounding Sphere
> algorithm" But I haven't seen/got any info on it.
> Has anyone any Documentation regarding this Subject?
> 

Two of the simplest methods are bounding sphere and bounding cuboid.

For bounding sphere, testing two objects to see if they collide
is just testing the distance between them versus the sum of the
two collision radii, 
i.e.
objects A and B in collision iff
{(Ax-Bx)**2 + (Ay-By)**2 +(Az-Bz)**2} 		// square of distance
< (A.collisionRadius + B.collisionRadius)**2	// square of legal dist

For bounding cuboid, it's just bounding rectangle extended;
for detection to be very fast, cuboids must be aligned in world
i.e. not rotated at arbitrary angle. It really is just using
bounding rectangle with an extra dimension check.


> 2. When Creating Environment Blocks in a Modeler are there any
> Special Considerations to Consider Regarding Collisions i.e. XYZ+-
> ect.

Given that collision detection is often a substantial CPU 
time-consumer, people often choose a fast algorithm and design a 
world around it (eg using bounding cuboids, and making the world
out of 3d grid blocks and spaces).
It depends how much collision detection you need to do, and how
much time it will actually take under different world
descriptions / polygonal building blocks.

> 
> 3. Has any One got any  Environment Blocks  I could use for Reference?
> This is so I  can see if I created my Models Correctly as I do not have
> any
> Info to Refer to. I have a Modeler & I created the blocks in my Project
> Myself,
> & I'm not sure I have done them correctly as the Frame Rate is Starting
> to suffer
> a Bit When I texture the Objects.

This may just be due to the number of objects and size/detail of the
textures, rather than any actual errors in creation.

> 
> 4. Can anyone point me in the direction of any Demos/Information/Sites
> ect
> Which Has any Environment Blocks/Collision Detection information?
> 
> I would be Grateful if any postings regarding this post could be sent to
> my IP
> Address as Well as the NewsGroup.
> 
> Thanks in Advance
> 
> --
> Cobra