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Math::ConvexHull(3)   User Contributed Perl Documentation  Math::ConvexHull(3)

       Math::ConvexHull	- Calculate convex hulls using Graham's	scan

	 use Math::ConvexHull qw/convex_hull/;
	 $hull_array_ref = convex_hull(\@points);

       "Math::ConvexHull" is a simple module that calculates convex hulls from
       a set of	points in 2D space. It is a straightforward implementation of
       the algorithm known as Graham's scan which, with	complexity of
       O(n*log(n)), is the fastest known method	of finding the convex hull of
       an arbitrary set	of points.  There are some methods of eliminating
       points that cannot be part of the convex	hull. These may	or may not be
       implemented in a	future version.

       The implementation cannot deal with duplicate points. Therefore,	points
       which are very, very close (think floating point	close) to the previous
       point are dropped since version 1.02 of the module.  However, if	you
       pass in randomly	ordered	data which contains duplicate points, this
       safety measure might not	help you. In that case,	you will have to
       remove duplicates yourself.

       None by default,	but you	may choose to have the "convex_hull()"
       subroutine exported to your namespace using standard Exporter

   convex_hull() subroutine
       "Math::ConvexHull" implements exactly one public	subroutine which,
       surprisingly, is	called "convex_hull()".	"convex_hull()"	expects	an
       array reference to an array of points and returns an array reference to
       an array	of points in the convex	hull.

       In this context,	a point	is considered to be a reference	to an array
       containing an x and a y coordinate. So an example use of
       "convex_hull()" would be:

	 use Data::Dumper;
	 use Math::ConvexHull qw/convex_hull/;

	 print Dumper convex_hull(
	   [0,0],     [1,0],
	   [0.2,0.9], [0.2,0.5],
	   [0,1],     [1,1],

	 # Prints out the points [0,0],	[1,0], [0,1], [1,1].

       Please note that	"convex_hull()"	does not return	copies of the points
       but instead returns the same array references that were passed in.

       New versions of this module can be found	on
       or CPAN.

       After implementing the algorithm	from my	CS notes, I found the exact
       same implementation in the German translation of	Orwant et al,
       "Mastering Algorithms with Perl". Their code reads better than mine, so
       if you looked at	the module sources and don't understand	what's going
       on, I suggest you have a	look at	the book.

       In early	2011, much of the module was rewritten to use the formulation
       of the algorithm	that was shown on the Wikipedia	article	on Graham's
       scan at the time. This takes care of issues with	including collinear
       points in the hull.


       One of these days, somebody should implement Chan's algorithm

       Steffen Mueller,	<>

       Copyright (C) 2003-2011 by Steffen Mueller

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself, either Perl	version	5.6 or,	at
       your option, any	later version of Perl 5	you may	have available.

perl v5.32.1			  2011-02-13		   Math::ConvexHull(3)


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