convexHull

CONVEXHULL Convex hull of a set of points.

   POLY = convexHull(POINTS)
   Computes the convex hull of the set of points POINTS. This function is
   mainly a wrapper to the convhull function, that format the result to a
   polygon.

   [POLY, INDS] = convexHull(POINTS)
   Also returns the indices of convex hull vertices within the original
   array of points.

   ... = convexHull(POINTS, 'simplify', BOOL)
   specifies the 'simplify' option use dfor calling convhull. By default,
   the convexHull functions uses simplify equals to TRUE (contrary to the
   convhull function), resulting in a more simple convex polygon.
   
   
   Example
     % Draws the convex hull of a set of random points
     pts = rand(30,2);
     drawPoint(pts, '.');
     hull = convexHull(pts);
     hold on; 
     drawPolygon(hull);

     % Draws the convex hull of a paper hen
     x = [0 10 20  0 -10 -20 -10 -10  0];
     y = [0  0 10 10  20  10  10  0 -10];
     poly = [x' y'];
     hull = convexHull(poly);
     figure; drawPolygon(poly);
     hold on; axis equal;
     drawPolygon(hull, 'm');

   See also
   polygons2d, convhull

0001 function [hull, inds] = convexHull(points, varargin)
0002 %CONVEXHULL Convex hull of a set of points.
0003 %
0004 %   POLY = convexHull(POINTS)
0005 %   Computes the convex hull of the set of points POINTS. This function is
0006 %   mainly a wrapper to the convhull function, that format the result to a
0007 %   polygon.
0008 %
0009 %   [POLY, INDS] = convexHull(POINTS)
0010 %   Also returns the indices of convex hull vertices within the original
0011 %   array of points.
0012 %
0013 %   ... = convexHull(POINTS, 'simplify', BOOL)
0014 %   specifies the 'simplify' option use dfor calling convhull. By default,
0015 %   the convexHull functions uses simplify equals to TRUE (contrary to the
0016 %   convhull function), resulting in a more simple convex polygon.
0017 %
0018 %
0019 %   Example
0020 %     % Draws the convex hull of a set of random points
0021 %     pts = rand(30,2);
0022 %     drawPoint(pts, '.');
0023 %     hull = convexHull(pts);
0024 %     hold on;
0025 %     drawPolygon(hull);
0026 %
0027 %     % Draws the convex hull of a paper hen
0028 %     x = [0 10 20  0 -10 -20 -10 -10  0];
0029 %     y = [0  0 10 10  20  10  10  0 -10];
0030 %     poly = [x' y'];
0031 %     hull = convexHull(poly);
0032 %     figure; drawPolygon(poly);
0033 %     hold on; axis equal;
0034 %     drawPolygon(hull, 'm');
0035 %
0036 %   See also
0037 %   polygons2d, convhull
0038 %
0039 
0040 % ------
0041 % Author: David Legland
0042 % e-mail: david.legland@nantes.inra.fr
0043 % Created: 2011-04-08,    using Matlab 7.9.0.529 (R2009b)
0044 % Copyright 2011 INRA - Cepia Software Platform.
0045 
0046 % checkup on array size
0047 if size(points, 1) < 3
0048     hull = points;
0049     inds = 1:size(points, 1);
0050     return;
0051 end
0052 
0053 % parse simplify option
0054 simplify = true;
0055 if nargin > 2 && strcmpi(varargin{1}, 'simplify')
0056     simplify = varargin{2};
0057 end
0058 
0059 % compute convex hull by calling the 'convhull' function
0060 inds = convhull(points(:,1), points(:,2), 'simplify', simplify);
0061 hull = points(inds, :);