contourMatrixToPolylines

CONTOURMATRIXTOPOLYLINES Converts a contour matrix array into a polyline set.

   POLYS = contourMatrixToPolylines(C)
   Converts the contour matrix array, as given as the result of the
   contourc function, into a set of polylines.

   Example
     img = imread('circles.png');
     C = contourc(img, 1);
     polys = contourMatrixToPolylines(C);
     imshow(img); hold on;
     drawPolyline(polys, 'Color', 'r', 'LineWidth', 2);

   See also
     polygons2d, contour, contourc

0001 function polys = contourMatrixToPolylines(C)
0002 %CONTOURMATRIXTOPOLYLINES Converts a contour matrix array into a polyline set.
0003 %
0004 %   POLYS = contourMatrixToPolylines(C)
0005 %   Converts the contour matrix array, as given as the result of the
0006 %   contourc function, into a set of polylines.
0007 %
0008 %   Example
0009 %     img = imread('circles.png');
0010 %     C = contourc(img, 1);
0011 %     polys = contourMatrixToPolylines(C);
0012 %     imshow(img); hold on;
0013 %     drawPolyline(polys, 'Color', 'r', 'LineWidth', 2);
0014 %
0015 %   See also
0016 %     polygons2d, contour, contourc
0017 
0018 % ------
0019 % Author: David Legland
0020 % e-mail: david.legland@grignon.inra.fr
0021 % Created: 2013-08-22,    using Matlab 7.9.0.529 (R2009b)
0022 % Copyright 2013 INRA - Cepia Software Platform.
0023 
0024 % size of the contour matrix array
0025 nCoords = size(C, 2);
0026 
0027 % first, compute the number of contours
0028 nContours = 0;
0029 offset = 1;
0030 while offset < nCoords
0031     nContours = nContours + 1;
0032     offset = offset + C(2, offset) + 1;
0033 end
0034 
0035 % extract each contour as a polygon or polyline
0036 polys = cell(nContours, 1);
0037 offset = 1;
0038 for iContour = 1:nContours
0039     nv = C(2, offset);
0040     polys{iContour} = C(:, offset + (1:nv))';
0041     offset = offset + nv + 1;
0042 end