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

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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);
  2 Comments
Julian Hapke
Julian Hapke on 19 Jun 2017
Edited: Julian Hapke on 19 Jun 2017
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!
Ba Ba Black Sheep! on 20 Jun 2017
This is incorrect answer. Using sind and cosd solved my problem.

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Answers (1)

Julian Hapke
Julian Hapke on 20 Jun 2017
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.

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