resamplePolyline

RESAMPLEPOLYLINE Distribute N points equally spaced on a polyline.

   RES = resamplePolyline(POLY, N)
   Resample the input polyline POLY such that the resulting polyline RES
   has N points. All points of RES belong to the initial polyline, but are
   not necessarily vertices.

   Example
     poly = [0 10;0 0;20 0];
     figure; drawPolyline(poly, 'b');
     poly2 = resamplePolyline(poly, 10);
     hold on; 
     drawPolyline(poly2, 'bo');
     axis equal; axis([-10 30 -10 20]);

   See also
     polygons2d, drawPolyline, resamplePolygon, resamplePolylineByLength

0001 function poly2 = resamplePolyline(poly, n)
0002 %RESAMPLEPOLYLINE Distribute N points equally spaced on a polyline.
0003 %
0004 %   RES = resamplePolyline(POLY, N)
0005 %   Resample the input polyline POLY such that the resulting polyline RES
0006 %   has N points. All points of RES belong to the initial polyline, but are
0007 %   not necessarily vertices.
0008 %
0009 %   Example
0010 %     poly = [0 10;0 0;20 0];
0011 %     figure; drawPolyline(poly, 'b');
0012 %     poly2 = resamplePolyline(poly, 10);
0013 %     hold on;
0014 %     drawPolyline(poly2, 'bo');
0015 %     axis equal; axis([-10 30 -10 20]);
0016 %
0017 %   See also
0018 %     polygons2d, drawPolyline, resamplePolygon, resamplePolylineByLength
0019 %
0020 
0021 % ------
0022 % Author: David Legland
0023 % e-mail: david.legland@inra.fr
0024 % Created: 2011-12-09,    using Matlab 7.9.0.529 (R2009b)
0025 % Copyrightf 2011 INRA - Cepia Software Platform.
0026 
0027 % parametrisation of the curve
0028 s = parametrize(poly);
0029 
0030 % distribute N points equally spaced
0031 Lmax = s(end);
0032 pos = linspace(0, Lmax, n);
0033 
0034 poly2 = zeros(n, size(poly, 2));
0035 for i = 1:n
0036     % index of surrounding vertices before and after
0037     ind0 = find(s <= pos(i), 1, 'last');
0038     ind1 = find(s >= pos(i), 1, 'first');
0039     
0040     if ind0 == ind1
0041         % get position of a vertex in input polyline
0042         poly2(i, :) = poly(ind0, :);
0043         continue;
0044     end
0045     
0046     % position of surrounding vertices
0047     pt0 = poly(ind0, :);
0048     pt1 = poly(ind1, :);
0049     
0050     % weights associated to each neighbor
0051     l0 = pos(i) - s(ind0);
0052     l1 = s(ind1) - pos(i);
0053     
0054     % linear interpolation of neighbor positions
0055     if (l0 + l1) > Lmax * 1e-12
0056         poly2(i, :) = (pt0 * l1 + pt1 * l0) / (l0 + l1);
0057     else
0058         % if neighbors are too close, do not use interpolation
0059         poly2(i, :) = pt0;
0060     end
0061 end