Code covered by the BSD License

geom2d

David Legland (view profile)

13 Jun 2005 (Updated )

Geometry library for matlab. Performs geometric computations on points, lines, circles, polygons...

polylinePoint(poly, pos)
```function point = polylinePoint(poly, pos)
%POLYLINEPOINT Extract a point from a polyline
%
%   POINT = polylinePoint(POLYLINE, POS)
%   POLYLINE is a N*2 array containing coordinate of polyline vertices
%   POS is comprised between 0 (first point of polyline) and Nv-1 (last
%   point of the polyline).
%
%
%   Example
%   poly = [10 10;20 10;20 20;30 30];
%   polylinePoint(poly, 0)
%       [10 10]
%   polylinePoint(poly, 3)
%       [30 30]
%   polylinePoint(poly, 1.4)
%       [20 14]
%
%
%   polygons2d
%
% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2009-04-30,    using Matlab 7.7.0.471 (R2008b)
% Copyright 2009 INRA - Cepia Software Platform.

% number of points to compute
Np = length(pos(:));

% number of vertices in polyline
Nv = size(poly, 1);

% allocate memory results
point = zeros(Np, 2);

% iterate on points
for i=1:Np
% compute index of edge (between 0 and Nv)
ind = floor(pos(i));

% special case of last point of polyline
if ind==Nv-1
point(i,:) = poly(end,:);
continue;
end

% format index to ensure being on polyline
ind = min(max(ind, 0), Nv-2);

% position on current edge
t = min(max(pos(i)-ind, 0), 1);

% parameters of current edge
x0 = poly(ind+1, 1);
y0 = poly(ind+1, 2);
dx = poly(ind+2,1)-x0;
dy = poly(ind+2,2)-y0;

% compute position of current point
point(i, :) = [x0+t*dx, y0+t*dy];
end
```