NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/graphics/8220

Internet Message Format | 1992-07-28 | 1.9 KB

Path: sparky!uunet!cis.ohio-state.edu!ucbvax!sequent.cc.hull.ac.uk!S.Marshall
From: [e-mail] (Simon Marshall)
Newsgroups: comp.graphics
Subject: Converting polygon with concave boundary to convex one anybody?
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Date: 28 Jul 92 12:40:51 GMT
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Hi all.  I mailed this question a while back, but shortly after the machine I
read news on hiccuped for a couple of days, and now I find out that our mailer
fails, with a loss of incoming mail, on a regular basis.  If you've responded
once, please do again, sorry!

I have a group of planar polygons with concave boundaries.  I wish to replace
each of these polygons with a number of triangular ones.  For a polygon with a
convex boundary, it's quiet easy.  All I do is pick a single polygon vertex and
form triangular facets, using this vertex, with successive pairs of vertices
around the polygon boundary.  The single polygon vertex is therefore common to
all triangular facets.

This, of course, will not work for polygons whose boundaries are concave, since
a triangular facet may lie outside the boundary of the polygon.  So either I
must use a different method of generating triangular facets, or firstly
generate polygons with convex boundaries from the polygons with concave
boundaries.

The $64M question is, how do I convert a concave polygon to a convex one?  I
thought there was a solution to this in Graphics GEMS, but nope...

Many thanks in advance!  Simon.
_______________________________________________________________________________
Simon Marshall, Dept. of Computer Science, University of Hull, Hull HU6 7RX, UK
  "Football isn't about life and death.  It's more important than that." Bill
Email: [e-mail]    Phone: [phone]    Fax: 466666   Shankley