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From: hutch@net1.ucsd.edu (Jim Hutchison)
Newsgroups: comp.graphics
Subject: Re: Request for info on octrees...
Message-ID: <1070@ucsd.EDU>
Date: 3 Aug 88 04:08:59 GMT
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Reply-To: hutch@net1.UUCP (Jim Hutchison)
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Octrees.  They are what they sound like, 8 legged trees.  Other than looking
like bizarre spiders, they are useful for subdividing 3-dimensional space.

You can subdivide a large box into 4 boxes on top of 4 other boxes.

This has been used to represent solid data with some heavy costs in memory
and speed (for images of "reasonable" resolution).  As solids, they have
some amazing properties.  You can do cut-aways and cross sections with
great facility, rotations are also quite reasonable.  Guess what, this
works out well for 3-D medical imaging.  You can find many of the ref's
for this type of application listed as "Voxels".  Pixar came out with a
product using what looked very very much like voxels, but they had another
name.  I am aware of why.

On another hand, since octrees subdivide space, you can use them as bounding
volumes for raytracing.  Put you objects in the appropriate leaf, and take
a modified (similiar to anti-aliased) Bresenham walk following your ray
through the 3 space described by the model & octree.

Beyond these vague gestulations, I don't know.

/*    Jim Hutchison   		UUCP:	{dcdwest,ucbvax}!cs!net1!hutch
		    		ARPA:	JHutchison@ucsd.edu		*/