Drawing a white line on an image using (rho, theta).

I want to draw a line on the following image using (| |rho , theta ) of the detected line using the Hough transformation.

.

expected output

.

What is wrong in the following code?

It's not being able to display the line.

input_image = gray_imread('Scratch1.1.png');

maxPeaks = 1; 
fillgap = 500; 
minline = 7; 

binary_image = edge(input_image,'canny');
[H,T,R] = hough(binary_image);
threshPeaks = ceil(0.3*max(H(:)));    
P  = houghpeaks(H, maxPeaks, 'threshold', threshPeaks);    
hlines = houghlines(binary_image, T, R, P, 'FillGap', fillgap, 'MinLength', minline);

h_line = hlines(1);

rho = h_line.rho;
theta = h_line.theta;

imshow(input_image);
hold on;
x = h_line.point1(1):h_line.point2(1);
y = (rho - x* cos(theta) )/ sin(theta);
plot(x,y);

[Julian Hapke]

There seems to be a Problem when you calculate x and y. The line is there but in the wrong location (try expanding the axis limits to see what I mean.) Also: Calculation of x and y (especially with interval 1 on x, it's just a line) is not necessary. If I use

hline = plot([h_line.point1(1) h_line.point2(1)],[h_line.point1(2) h_line.point2(2)],'w')

I get the results you seem to be expecting.

[Ba Ba Black Sheep!]

This is incorrect answer. Using sind and cosd solved my problem.

Answer 1

[Julian Hapke]

My comment was the answer, so to stick to the structure of this forum:

Your calculation of x and y yields to wrong values. If you use the end points of the houghlines directly

hline = plot([h_line.point1(1) h_line.point2(1)],[h_line.point1(2) h_line.point2(2)],'w')

you get the line you showed in your "expected output"

Please mark this as answer if it fits your needs.