function pos = edgePosition(point, edge, varargin)
%EDGEPOSITION Return position of a point on an edge.
%
%   POS = edgePosition(POINT, EDGE);
%   Computes position of point POINT on the edge EDGE, relative to the
%   position of edge vertices.
%   EDGE has the form [x1 y1 x2 y2],
%   POINT has the form [x y], and is assumed to belong to edge supporting
%   line. The result POS has the following meaning:
%     POS < 0:      POINT is located before the first vertex
%     POS = 0:      POINT is located on the first vertex
%     0 < POS < 1:  POINT is located between the 2 vertices (on the edge)
%     POS = 1:      POINT is located on the second vertex
%     POS > 1:      POINT is located after the second vertex
%
%   POS = edgePosition(POINT, EDGES);
%   If EDGES is an array of NL edges, return NE positions, corresponding to
%   each edge.
%
%   POS = edgePosition(POINTS, EDGE);
%   If POINTS is an array of NP points, return NP positions, corresponding
%   to each point.
%
%   POS = edgePosition(POINTS, EDGES);
%   If POINTS is an array of NP points and EDGES is an array of NE edges,
%   return an array of [NP NE] position, corresponding to each couple
%   point-edge.
%
%   POS = edgePosition(POINTS, EDGES, 'diag');
%   When POINTS and EDGES are two arrays with same number of rows, returns
%   single column vector corresponding to each pair of point-edge.
%
%   See also 
%     edges2d, createEdge, isPointOnEdge, edgeToLine
%

% ------
% Author: David Legland
% E-mail: david.legland@inrae.fr
% Created: 2004-05-25
% Copyright 2004-2024 INRA - Cepia Software Platform

% parse input options
diag = false;
if ~isempty(varargin) && strcmp(varargin{1}, 'diag')
    diag = true;
end

% number of points and of edges
nEdges = size(edge, 1);
nPoints = size(point, 1);

if nPoints == nEdges && diag
    % reshape into N-by-1 arrays
    dxe = (edge(:,3) - edge(:,1));
    dye = (edge(:,4) - edge(:,2));
    dxp = point(:,1) - edge(:,1);
    dyp = point(:,2) - edge(:,2);
else
    % reshape arrays to result in NP-by-NE arrays
    dxe = (edge(:,3) - edge(:,1))';
    dye = (edge(:,4) - edge(:,2))';
    dxp = bsxfun(@minus, point(:,1), edge(:,1)');
    dyp = bsxfun(@minus, point(:,2), edge(:,2)');
end

% compute position
pos = (dxp .* dxe + dyp .* dye) ./ (dxe .* dxe + dye .* dye);
