projPointOnPolygon

PROJPOINTONPOLYGON  Compute position of a point projected on a polygon.

   POS = projPointOnPolygon(POINT, POLYGON)
   Compute the position of the orthogonal projection of a point on a
   polygon.
   POINT is a 1-by-2 row vector containing point coordinates
   POLYGON is a N-by-2 array containing coordinates of polygon vertices

   When POINT is an array of points, returns a column vector with as many
   rows as the number of points. 

   [POS, DIST] = projPointOnPolygon(...)
   Also returns the distance between POINT and POLYGON. The distance is
   negative if the point is located inside of the polygon.

   Example
     poly = [10 10; 20 10;20 20;10 20];
     projPointOnPolygon([15 0], poly)
     ans =
         0.5000
     projPointOnPolygon([0 16], poly)
     ans =
         3.4000

   See also
   points2d, polygons2d, polygonPoint, projPointOnPolyline
   distancePointpolygon

0001 function varargout = projPointOnPolygon(point, poly, varargin)
0002 %PROJPOINTONPOLYGON  Compute position of a point projected on a polygon.
0003 %
0004 %   POS = projPointOnPolygon(POINT, POLYGON)
0005 %   Compute the position of the orthogonal projection of a point on a
0006 %   polygon.
0007 %   POINT is a 1-by-2 row vector containing point coordinates
0008 %   POLYGON is a N-by-2 array containing coordinates of polygon vertices
0009 %
0010 %   When POINT is an array of points, returns a column vector with as many
0011 %   rows as the number of points.
0012 %
0013 %   [POS, DIST] = projPointOnPolygon(...)
0014 %   Also returns the distance between POINT and POLYGON. The distance is
0015 %   negative if the point is located inside of the polygon.
0016 %
0017 %   Example
0018 %     poly = [10 10; 20 10;20 20;10 20];
0019 %     projPointOnPolygon([15 0], poly)
0020 %     ans =
0021 %         0.5000
0022 %     projPointOnPolygon([0 16], poly)
0023 %     ans =
0024 %         3.4000
0025 %
0026 %   See also
0027 %   points2d, polygons2d, polygonPoint, projPointOnPolyline
0028 %   distancePointpolygon
0029 %
0030 
0031 % ------
0032 % Author: David Legland
0033 % e-mail: david.legland@grignon.inra.fr
0034 % Created: 2009-04-30,    using Matlab 7.7.0.471 (R2008b)
0035 % Copyright 2009 INRA - Cepia Software Platform.
0036 
0037 
0038 % eventually copy first point at the end to ensure closed polygon
0039 if sum(poly(end, :) == poly(1,:)) ~= 2
0040     poly = [poly; poly(1,:)];
0041 end
0042 
0043 % compute position wrt outline
0044 [pos, minDist] = projPointOnPolyline(point, poly);
0045 
0046 % process output arguments
0047 if nargout <= 1
0048     varargout{1} = pos;
0049 elseif nargout == 2
0050     varargout{1} = pos;
0051     if inpolygon(point(:,1), point(:,2), poly(:,1), poly(:,2))
0052         minDist = -minDist;
0053     end
0054     varargout{2} = minDist;
0055 end