function [yline xline] = drawslope(I, alpha, refpoint)
%
% function to draw a line at a desired angle <alpha>,
% which goes through a reference point <refpoint>
% function inputs:
% <I>: Image for which the drawing is desired.
% Range:3Dim, grayscale, or logical
% <alpha>: Angle in degrees, where 0 is complete horizontal
% Range: -Inf - +Inf (cyclic after + (-) 180 degrees of course)
% <refpoint> : Reference interception point with the slope
% Range: A varaible of size 2x1, where refpoint(1) is horizontal and (2) is vertical
% function outputs:
% <yline> : Y axis coordinates of both line ends
% <xline>: X axis coordinates of both line ends
%
% outputs should be used with plot function as following:
% plot(yline,xline,...plot specifiers)
%
% Example usage:
% Image = imread('someImage');
% image_centroid = [100 240];
% [yline xline] = drawslope(Image, -60, image_centroid);
% imshow(Image);
% hold on;
% plot(yline, xline, 'blue','LineWidth',2);
%
%
% Written by Elad Boneh, 15.8.2009
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
[x y z] = size(I);
%Infinite lines protection
if (mod(alpha,180) < 0.01)
alpha = 0.01;
elseif (mod(alpha,90) < 0.01)
alpha = 90.001;
end
horizontal_distance = ((refpoint(2)-1)/tand(alpha));
if ((refpoint(1) + horizontal_distance) > y)
vertical_distance = ((refpoint(1)-1)/cotd(alpha));
verctical_distance_reversed = ((y-refpoint(1))/cotd(alpha));
xline = [(refpoint(2) + vertical_distance), (refpoint(2) - verctical_distance_reversed)];
yline = [1, y];
else
horizontal_distance_reversed = ((x-refpoint(2))/tand(alpha));
xline = [1, x];
yline = [(refpoint(1)+ horizontal_distance), (refpoint(1)- horizontal_distance_reversed)];
end
