polygonSignature

POLYGONSIGNATURE Polar signature of a polygon (polar distance to origin).

   DISTS = polygonSignature(POLY, THETALIST)
   Computes the polar signature of a polygon, for a set of angles in
   degrees. If a ray at a given angle does not intersect the polygon, the
   corresponding distance value is set to NaN.

   DISTS = polygonSignature(POLY, N)
   When N is a scalar, uses N angles equally distributed between 0 and 360
   degrees.
   
   [DISTS, THETA] = polygonSignature(...)
   Also returns the angle set for which the signature was computed.

   Example
   polygonSignature

   See also
     polygons2d, signatureToPolygon, intersectRayPolygon

0001 function [res, thetaList] = polygonSignature(poly, varargin)
0002 %POLYGONSIGNATURE Polar signature of a polygon (polar distance to origin).
0003 %
0004 %   DISTS = polygonSignature(POLY, THETALIST)
0005 %   Computes the polar signature of a polygon, for a set of angles in
0006 %   degrees. If a ray at a given angle does not intersect the polygon, the
0007 %   corresponding distance value is set to NaN.
0008 %
0009 %   DISTS = polygonSignature(POLY, N)
0010 %   When N is a scalar, uses N angles equally distributed between 0 and 360
0011 %   degrees.
0012 %
0013 %   [DISTS, THETA] = polygonSignature(...)
0014 %   Also returns the angle set for which the signature was computed.
0015 %
0016 %   Example
0017 %   polygonSignature
0018 %
0019 %   See also
0020 %     polygons2d, signatureToPolygon, intersectRayPolygon
0021 %
0022 
0023 % ------
0024 % Author: David Legland
0025 % e-mail: david.legland@nantes.inra.fr
0026 % Created: 2013-03-14,    using Matlab 7.9.0.529 (R2009b)
0027 % Copyright 2013 INRA - Cepia Software Platform.
0028 
0029 % default angle list
0030 thetaList = 0:359;
0031 
0032 % get user-defined angle list
0033 if ~isempty(varargin)
0034     var = varargin{1};
0035     if isscalar(var)
0036         thetaList = linspace(0, 360, var+1);
0037         thetaList(end) = [];
0038     else
0039         thetaList = var;
0040     end
0041 end
0042 
0043 % also extract reference point if needed
0044 center = [0 0];
0045 if nargin > 2
0046     center = varargin{2};
0047 end
0048 
0049 % allocate memory
0050 nTheta = length(thetaList);
0051 res = NaN * ones(nTheta, 1);
0052 
0053 % iterate on angles
0054 for i = 1:length(thetaList)
0055     theta = deg2rad(thetaList(i));
0056     ray = [center cos(theta) sin(theta)];
0057 
0058     ptInt = intersectRayPolygon(ray, poly);
0059     if ~isempty(ptInt)
0060         res(i) = distancePoints(center, ptInt(1,:));
0061     end
0062 end