Path: utzoo!attcan!uunet!lll-winken!lll-lcc!crawfis
From: crawfis@lll-lcc.aRpA (Roger A. Crawfis)
Newsgroups: comp.graphics
Subject: Re: Polygon-related questions
Message-ID: <1753@lll-lcc.aRpA>
Date: 14 Jul 88 16:23:03 GMT
References: <4460@csli.STANFORD.EDU> <25033@ucbvax.BERKELEY.EDU> <1751@lll-lcc.aRpA> <25059@ucbvax.BERKELEY.EDU> <13173@jumbo.dec.com>
Reply-To: crawfis@lll-lcc.llnl.gov.UUCP (Roger A. Crawfis)
Organization: Lab Comp Ctr, Lawrence Laboratory, Livermore Ca
Lines: 28


I appollogize for my misprint in the original posting, but what I 
meant to say is:  What if we do not want the convex region, but 
rather want to get some sort of concave polygon (or polyhedron) from
the points?  My feeling is that this will be ill-defined.

For example, if we had the 2D scattered data points:

        x                             x


        x    0   0     0      x   0 0     x


               x                       x

where I will call the x's exterior points and the 0's interior points.

The blob we are looking for consists of the x's.  However note that in
this case there are 2 such blobs, one with the middle x (on the 2nd line)
connected with the top and one with it connected with the bottom (a third
could also be with the middle point connected to both the top and the
bottom, but in 3D I want a solid non-disjoint blob).  Now the convex hull
can probably be applied to sections of this at a time, but what sections?
This also leads to some sort of partitioning problem as I mentioned 
earlier.  Any more ideas?

Roger A. Crawfis
Lawrence Livermore National Lab