RobotStudio/smtb/homline.m
%HOMLINE Homogeneous line from two points
%
% L = HOMLINE(X1, Y1, X2, Y2) is a vector (3x1) which describes a line in
% homogeneous form that contains the two Euclidean points (X1,Y1) and (X2,Y2).
%
% Homogeneous points X (3x1) on the line must satisfy L'*X = 0.
%
% See also PLOT_HOMLINE.

% Copyright (C) 1993-2019 Peter I. Corke
%
% This file is part of The Spatial Math Toolbox for MATLAB (SMTB).
% 
% Permission is hereby granted, free of charge, to any person obtaining a copy
% of this software and associated documentation files (the "Software"), to deal
% in the Software without restriction, including without limitation the rights
% to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
% of the Software, and to permit persons to whom the Software is furnished to do
% so, subject to the following conditions:
%
% The above copyright notice and this permission notice shall be included in all
% copies or substantial portions of the Software.
%
% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
% FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
% COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
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% CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
%
% https://github.com/petercorke/spatial-math

% TODO, probably should be part of a HomLine class.

function l = homline(x1, y1, x2, y2)

    l = cross([x1 y1 1], [x2 y2 1]);

    % normalize so that the result of x*l' is the pixel distance
    % from the line
    l = l / norm(l(1:2));
