find longest hough line in matlab

To find the longest Hough line in Matlab, you can use the Hough Transform algorithm for line detection on your image. This algorithm identifies candidate lines by a voting procedure and then clusters them to produce more accurate lines. Once the lines have been detected, you can then find the longest line using the distance formula.

Here are the steps to find the longest Hough line in Matlab:

1. First, read in your image and convert it to grayscale:

main.m
img = imread('image.jpg');
gray_img = rgb2gray(img);
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2. Next, apply the edge detection algorithm to extract the edges of the image:

main.m
edges_img = edge(gray_img);
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3. Use the Hough Transform to detect the lines in the edge image:

main.m
[H,T,R] = hough(edges_img);
P  = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
lines = houghlines(edges_img,T,R,P,'FillGap',5,'MinLength',7);
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4. Iterate through the detected lines, and calculate the length of each line using the distance formula:

main.m
max_len = 0;

for k = 1:length(lines)
    xy = [lines(k).point1; lines(k).point2];
    len = norm(lines(k).point1 - lines(k).point2);
    if ( len > max_len)
        max_len = len;
        xy_long = xy;
    end
end
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5. The longest line will be stored in the xy_long variable, which contains the coordinates of the endpoints of the line. You can draw the line on the image by using the line function:

main.m
figure, imshow(img), hold on
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','green');
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This will plot the detected longest Hough line on the original image.