how to get a line information after applying the houghlines

Hello.

I want to measure the terrain slope angle from the terrain image file. so I used some preferred code from the community. which is below.

   I  = imread('IMG.tif');
       rotI = imrotate(I, 0 ,'crop');
       BW = edge(rotI,'canny');
       [H,T,R] = hough(BW);
       imshow(H,[],'XData',T,'YData',R,'InitialMagnification','fit');
       xlabel('\theta'), ylabel('\rho');
       axis on, axis normal, hold on;
       P  = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
       x = T(P(:,2)); 
       y = R(P(:,1));
       plot(x,y,'s','color','white');

       % Find lines and plot them
       lines = houghlines(BW,T,R,P,'FillGap',5,'MinLength',7);
       figure, imshow(rotI), hold on
       max_len = 0;
       for k = 1:length(lines)
         xy = [lines(k).point1; lines(k).point2];
         plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');

         % plot beginnings and ends of lines
         plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
         plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');

         % determine the endpoints of the longest line segment 
         len = norm(lines(k).point1 - lines(k).point2);
         if ( len > max_len)
           max_len = len;
           xy_long = xy;
         end
       end

so, I got some lines on the image. however, how to measure the drawn lines information? is it possible to get such information, slope angle, from the lines?

Please let me know!

Answer 1

[Jiro Doke]

In your example, the variable lines has the information about the straight lines. Double-click the variable in the Workspace. You will see that it has the coordinates of the end points of the lines ( point1 and point2 ). Also, theta gives you the angle information. 90 - theta is the actual angle of the lines, measured counter-clockwise from +x axis.

[soyoung shin]

Thank you so much for your answer. I will check it!

[soyoung shin]

Can I display the lines information on the figure windows?