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From: jroth@allvax.dec.com (Jim Roth)
Newsgroups: comp.graphics
Subject: Re: Hidden lines on plotter
Message-ID: <3014@ryn.esg.dec.com>
Date: 4 Oct 90 11:15:09 GMT
Sender: guest@ryn.esg.dec.com
Organization: Digital Equipment Corporation
Lines: 35


In article <3397@mindlink.UUCP>, a575@mindlink.UUCP (Michael G. Henders) writes...
>Sorry, I've lost the original postings here, but...
> 
> [ ... followup giving Leendert Ammeralls book ... ]

Thanks, I'd forgotten to follow up on that... I bought the book for
exactly the same reason Michael did - its hidden line code!

Here is the citation for the COSMIC software I mentioned:

	M87-10038 - NASA Dryden Flight Research Center
	Hidden Line Computer Code
	D. R. Hedgley

I don't know if the source is online anywhere, though I have a copy of the
indigestable FORTRAN code itself backed up somewhere.  To decipher it you'd
have to get a copy of the technical report - the code has *no* comments!
We're talking dusty deckware.

I also wanted to mention that plane sweep algorithms while rather neat in
theory can have problems dealing with degenerate cases (multiple
edges at a vertex, edges with an endpoint epsilon from another edge, etc.)
which are a real headache in practice.

Though there has been some work on resolving this (so-called "simulation of
simplicity" by Guibas et al) I'm unsure how practical such solutions really
are.  In 2-D it is possible to use rational arithmetic and get a reasonable
and reliable implementation, but in 3D it looks bad.  I haven't gotten very
far with such problems yet.

Making plane sweep algorithms reliable in the face of such problems is
an active area of research.

- Jim