%% Copyright (c) 2011, INRA
%% 2003-2011, David Legland <david.legland@grignon.inra.fr>
%% 2011 Adapted to Octave by Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
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%% -*- texinfo -*-
%% @deftypefn {Function File} {@var{theta} =} lineAngle(varargin)
%% Computes angle between two straight lines
%%
%%   A = lineAngle(LINE);
%%   Returns the angle between horizontal, right-axis and the given line.
%%   Angle is fiven in radians, between 0 and 2*pi, in counter-clockwise
%%   direction.
%%
%%   A = lineAngle(LINE1, LINE2);
%%   Returns the directed angle between the two lines. Angle is given in
%%   radians between 0 and 2*pi, in counter-clockwise direction.
%% 
%% @seealso{lines2d, angles2d, createLine, normalizeAngle}
%% @end deftypefn

function theta = lineAngle(varargin)

  nargs = length(varargin);
  if nargs == 1
      % angle of one line with horizontal
      line = varargin{1};
      theta = mod(atan2(line(:,4), line(:,3)) + 2*pi, 2*pi);
      
  elseif nargs==2
      % angle between two lines
      theta1 = lineAngle(varargin{1});
      theta2 = lineAngle(varargin{2});
      theta = mod(bsxfun(@minus, theta2, theta1)+2*pi, 2*pi);
  end

endfunction

% horizontal
%!test
%! line1 = createLine([2 3 1 0]);
%! assert (lineAngle(line1), 0, 1e-6);

%!test
%! line1 = createLine([2 3 0 1]);
%! assert (lineAngle(line1), pi/2, 1e-6);

%!test
%! line1 = createLine([2 3 1 1]);
%! assert (lineAngle(line1), pi/4, 1e-6);

%!test
%! line1 = createLine([2 3 5 -1]);
%! assert (lineAngle(line1), mod(atan2(-1, 5)+2*pi, 2*pi), 1e-6);

%!test
%! line1 = createLine([2 3 5000 -1000]);
%! assert (lineAngle(line1), mod(atan2(-1, 5)+2*pi, 2*pi), 1e-6);

%!test
%! line1 = createLine([2 3 -1 0]);
%! assert (lineAngle(line1), pi, 1e-6);

% test lineAngle with two parameters : angle between 2 lines
% check for 2 orthogonal lines
%!test
%! line1 = createLine([1 3 1 0]);
%! line2 = createLine([-2 -1 0 1]);
%! assert (lineAngle(line1, line2), pi/2, 1e-6);
%! assert (lineAngle(line2, line1), 3*pi/2, 1e-6);

% check for 2 orthogonal lines, with very different parametrizations
%!test
%! line1 = createLine([1 3 1 1]);
%! line2 = createLine([-2 -1 -1000 1000]);
%! assert (lineAngle(line1, line2), pi/2, 1e-6);
%! assert (lineAngle(line2, line1), 3*pi/2, 1e-6);
