Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / geometry-1.5.0 / polygons2d / polygonSelfIntersections.m

diff --git a/octave_packages/geometry-1.5.0/polygons2d/polygonSelfIntersections.m b/octave_packages/geometry-1.5.0/polygons2d/polygonSelfIntersections.m
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+## 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