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Math::ConvexHull::MonotoneChain - Andrew's monotone chain algorithm for finding a convex hull in 2D


  use Math::ConvexHull::MonotoneChain 'convex_hull';
  my $ch = convex_hull(
      [0, 0],
      [0, 1],
      [1, 0],
      [0.5, 0.5],
      [1, 1],
  # $ch is now:
  # [ [0, 0],
  #   [1, 0],
  #   [1, 1],
  #   [0, 1], ]


This is somewhat experimental still.

This (XS) module optionally exports a single function convex_hull which calculates the convex hull of the input points and returns it. The algorithm is O(n log n) due to having to sort the input list, but should be somewhat faster than a plain Graham's scan (also O(n log n)) in practice since it avoids polar coordinates.



Expects an array ref of points as input, returns an array ref of of the points in the convex hull, ordered counter-clockwise.

point refers to an array reference containing an X, and a Y coordinate.

For less than three input points, this will return an array reference whose elements are the input points (without cloning).


Math::ConvexHull, which uses Graham's scan in pure Perl.


Steffen Mueller, <>


Copyright (C) 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 5.8.0 or, at your option, any later version of Perl 5 you may have available.