Math::ConvexHull(3) Calculate convex hulls using Graham's scan (n*log(n))


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 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 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.


Steffen Mueller, <[email protected]>


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.