+## Copyright (C) 2003-2011 David Legland <david.legland@grignon.inra.fr>
+## Copyright (C) 2012 Adapted to Octave by Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
+## All rights reserved.
+##
+## Redistribution and use in source and binary forms, with or without
+## modification, are permitted provided that the following conditions are met:
+##
+## 1 Redistributions of source code must retain the above copyright notice,
+## this list of conditions and the following disclaimer.
+## 2 Redistributions in binary form must reproduce the above copyright
+## notice, this list of conditions and the following disclaimer in the
+## documentation and/or other materials provided with the distribution.
+##
+## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ''AS IS''
+## AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+## IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+## ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
+## ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+## DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+## SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+## CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+## OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+##
+## The views and conclusions contained in the software and documentation are
+## those of the authors and should not be interpreted as representing official
+## policies, either expressed or implied, of the copyright holders.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{pts} = } polygonSelfIntersections (@var{poly})
+## @deftypefnx {Function File} {[@var{pts} @var{pos1} @var{pos2}] = } polygonSelfIntersections (@var{poly})
+## Find-self intersection points of a polygon
+##
+## Return the position of self intersection points
+##
+## Also return the 2 positions of each intersection point (the position
+## when meeting point for first time, then position when meeting point
+## for the second time).
+##
+## Example
+## @example
+## # use a '8'-shaped polygon
+## poly = [10 0;0 0;0 10;20 10;20 20;10 20];
+## polygonSelfIntersections(poly)
+## ans =
+## 10 10
+## @end example
+##
+## @seealso{polygons2d, polylineSelfIntersections}
+## @end deftypefn
+
+function varargout = polygonSelfIntersections(poly, varargin)
+
+ tol = 1e-14;
+
+ # ensure the last point equals the first one
+ if sum(abs(poly(end, :)-poly(1,:)) < tol) ~= 2
+ poly = [poly; poly(1,:)];
+ end
+
+ # compute intersections by calling algo for polylines
+ [points pos1 pos2] = polylineSelfIntersections(poly);
+
+ # It may append that first vertex of polygon is detected as intersection,
+ # the following tries to detect this
+ n = size(poly, 1) - 1;
+ inds = (pos1 == 0 & pos2 == n) | (pos1 == n & pos2 == 0);
+ points(inds, :) = [];
+ pos1(inds) = [];
+ pos2(inds) = [];
+
+ # remove multiple intersections
+ [points I J] = unique(points, 'rows', 'first'); ##ok<NASGU>
+ pos1 = pos1(I);
+ pos2 = pos2(I);
+
+
+ ## Post-processing
+
+ # process output arguments
+ if nargout <= 1
+ varargout = {points};
+ elseif nargout == 3
+ varargout = {points, pos1, pos2};
+ end
+
+endfunction