Code covered by the BSD License  

Highlights from
geom2d

image thumbnail

geom2d

by

 

13 Jun 2005 (Updated )

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

isPointOnEdge(point, edge, varargin)
function b = isPointOnEdge(point, edge, varargin)
%ISPOINTONEDGE Test if a point belongs to an edge
%
%   Usage
%   B = isPointOnEdge(POINT, EDGE)
%   B = isPointOnEdge(POINT, EDGE, TOL)
%
%   Description
%   B = isPointOnEdge(POINT, EDGE)
%   with POINT being [xp yp], and EDGE being [x1 y1 x2 y2], returns TRUE if
%   the point is located on the edge, and FALSE otherwise.
%
%   B = isPointOnEdge(POINT, EDGE, TOL)
%   Specify an optilonal tolerance value TOL. The tolerance is given as a
%   fraction of the norm of the edge direction vector. Default is 1e-14. 
%
%   B = isPointOnEdge(POINTARRAY, EDGE)
%   B = isPointOnEdge(POINT, EDGEARRAY)
%   When one of the inputs has several rows, return the result of the test
%   for each element of the array tested against the single parameter.
%
%   B = isPointOnEdge(POINTARRAY, EDGEARRAY)
%   When both POINTARRAY and EDGEARRAY have the same number of rows,
%   returns a column vector with the same number of rows.
%   When the number of rows are different and both greater than 1, returns
%   a Np-by-Ne matrix of booleans, containing the result for each couple of
%   point and edge.
%
%   Examples
%   % create a point array
%   points = [10 10;15 10; 30 10];
%   % create an edge array
%   vertices = [10 10;20 10;20 20;10 20];
%   edges = [vertices vertices([2:end 1], :)];
%
%   % Test one point and one edge
%   isPointOnEdge(points(1,:), edges(1,:))
%   ans = 
%       1
%   isPointOnEdge(points(3,:), edges(1,:))
%   ans = 
%       0
%
%   % Test one point and several edges
%   isPointOnEdge(points(1,:), edges)'
%   ans =
%        1     0     0     1
%
%   % Test several points and one edge
%   isPointOnEdge(points, edges(1,:))'
%   ans =
%        1     1     0
%
%   % Test N points and N edges
%   isPointOnEdge(points, edges(1:3,:))'
%   ans =
%        1     0     0
%
%   % Test NP points and NE edges
%   isPointOnEdge(points, edges)
%   ans =
%        1     0     0     1
%        1     0     0     0
%        0     0     0     0
%
%
%   See also
%   edges2d, points2d, isPointOnLine
%
%   ---------
%   author : David Legland 
%   INRA - TPV URPOI - BIA IMASTE
%   created the 31/10/2003.
%

%   HISTORY
%   11/03/2004 change input format: edge is [x1 y1 x2 y2].
%   17/01/2005 if test N edges with N points, return N boolean.
%   21/01/2005 normalize test for colinearity, so enhance precision
%   22/05/2009 rename to isPointOnEdge, add psb to specify tolerance
%   26/01/2010 fix bug in precision computation
%   04/10/2010 fix a bug, and clean up code
%   28/10/2010 fix bug to have N results when input is N points and N
%       edges, add support for arrays with different numbers of rows, and
%       update doc.
%   2011-06-15 rewrites by using less memory, and avoiding repmat when psb


% extract computation tolerance
tol = 1e-14;
if ~isempty(varargin)
    tol = varargin{1};
end

% number of edges and of points
Np = size(point, 1);
Ne = size(edge, 1);

% adapt size of inputs if needed, and extract elements for computation
if Np == Ne
    % When the number of points and edges is the same, the one-to-one test
    % will be computed, so there is no need to repeat matrices
    dx = edge(:,3) - edge(:,1);
    dy = edge(:,4) - edge(:,2);
    lx = point(:,1) - edge(:,1);
    ly = point(:,2) - edge(:,2);
    
elseif Np == 1
    % one point, several edges
    dx = edge(:, 3) - edge(:, 1);
    dy = edge(:, 4) - edge(:, 2);
    lx = point(ones(Ne, 1), 1) - edge(:, 1);
    ly = point(ones(Ne, 1), 2) - edge(:, 2);
    
elseif Ne == 1
    % several points, one edge
    dx = (edge(3) - edge(1)) * ones(Np, 1);
    dy = (edge(4) - edge(2)) * ones(Np, 1);
    lx = point(:, 1) - edge(1);
    ly = point(:, 2) - edge(2);

else
    % Np points and Ne edges:
    % Create an array for each parameter, so that the result will be a
    % Np-by-Ne matrix of booleans (requires more memory, and uses repmat)

    x0 = repmat(edge(:, 1)', Np, 1);
    y0 = repmat(edge(:, 2)', Np, 1);
    dx = repmat(edge(:,3)', Np,  1) - x0;
    dy = repmat(edge(:,4)', Np,  1) - y0;
    
    lx = repmat(point(:, 1), 1, Ne) - x0;
    ly = repmat(point(:, 2), 1, Ne) - y0;
end

% test if point is located on supporting line
b1 = (abs(lx.*dy - ly.*dx) ./ hypot(dx, dy)) < tol;

% compute position of point with respect to edge bounds
% use different tests depending on line angle
ind     = abs(dx) > abs(dy);
t       = zeros(size(dx));
t(ind)  = lx( ind) ./ dx( ind);
t(~ind) = ly(~ind) ./ dy(~ind);

% check if point is located between edge bounds
b = t >- tol & t-1 < tol & b1;

Contact us