function value = lrline ( xu, yu, xv1, yv1, xv2, yv2, dv )
%*****************************************************************************80
%
%% lrline() determines if a point is left of, right or, or on a directed line.
%
% Discussion:
%
% The directed line is parallel to, and at a signed distance DV from
% a directed base line from (XV1,YV1) to (XV2,YV2).
%
% Licensing:
%
% This code is distributed under the GNU LGPL license.
%
% Modified:
%
% 07 February 2005
%
% Author:
%
% Original FORTRAN77 version by Barry Joe,
% MATLAB version by John Burkardt
%
% Reference:
%
% Barry Joe,
% GEOMPACK - a software package for the generation of meshes
% using geometric algorithms,
% Advances in Engineering Software,
% Volume 13, pages 325-331, 1991.
%
% Input:
%
% real XU, YU, the coordinates of the point whose
% position relative to the directed line is to be determined.
%
% real XV1, YV1, XV2, YV2, the coordinates of two points
% that determine the directed base line.
%
% real DV, the signed distance of the directed line
% from the directed base line through the points (XV1,YV1) and (XV2,YV2).
% DV is positive for a line to the left of the base line.
%
% Output:
%
% integer VALUE, the result:
% +1, the point is to the right of the directed line;
% 0, the point is on the directed line;
% -1, the point is to the left of the directed line.
%
tol = 100.0 * eps;
dx = xv2 - xv1;
dy = yv2 - yv1;
dxu = xu - xv1;
dyu = yu - yv1;
tolabs = tol * max ( abs ( dx ), ...
max ( abs ( dy ), ...
max ( abs ( dxu ), ...
max ( abs ( dyu ), abs ( dv ) ) ) ) );
t = dy * dxu - dx * dyu + dv * sqrt ( dx * dx + dy * dy );
if ( tolabs < t )
value = 1;
elseif ( -tolabs <= t )
value = 0;
else
value = -1;
end
return
end