NAME

Math::ConvexHull - Calculate convex hulls using Graham's scan (n*log(n))

SYNOPSIS

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

DESCRIPTION

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.

EXPORT

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

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 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.

AUTHOR

Steffen Mueller, <hull-module at steffen-mueller dot net>

SEE ALSO

New versions of this module can be found on http://steffen-mueller.net 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.