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geom2d

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geom2d

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13 Jun 2005 (Updated )

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

nndist(points)
function [dists, neighInds] = nndist(points)
%NNDIST  Nearest-neighbor distances of each point in a set
%
%   DISTS = nndist(POINTS)
%   Returns the distance to the nearest enighbor of each point in the given
%   pattern.
%   POINTS is an array of points, NP-by-ND.
%   DISTS is a NP-by-1 array containing the distances to the nearest
%   neighbor.
%
%   This functions first computes the Delaunay triangulation of the set of
%   points, then search for nearest distance in the set of each vertex
%   neighbors. This reduces the overall complexity, but difference was
%   noticed only for large sets (>10000 points)
%
%   Example
%     % Display Stienen diagram of a set of random points in unit square
%     pts = rand(100, 2);
%     dists = nndist(pts);
%     figure; drawPoint(pts, '.');
%     hold on; drawCircle([pts dists/2]);
%     axis equal; axis([-.1 1.1 -.1 1.1]);
%
%   See also
%     points2d, distancePoints, minDistancePoints
%
% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2011-12-01,    using Matlab 7.9.0.529 (R2009b)
% Copyright 2011 INRA - Cepia Software Platform.

n = size(points, 1);

dists = zeros(n, 1);
neighInds = zeros(n, 1);

tri = DelaunayTri(points);

% compute distance to nearest neighbor of each point in the pattern
for i = 1:n
    % find indices of neighbor vertices in Delaunay Triangulation.
    % this contains the nearest neighbor
    inds = unique(tri.Triangulation(sum(tri.Triangulation == i, 2) > 0, :));
    
    % compute minimal distance 
    [dists(i), indN] = min(distancePoints(points(i,:), points(inds(inds~=i), :)));
    neighInds(i) = inds(indN);
end

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