Home Hough Transform: Converted polar coordinates back to Cartesian, but still can't plot them
 So I have already implemented every part of a Hough Transform on my own, except for actually plotting the lines back onto the original image. I can set up my array of data that I have like this. points | theta | rho -------|-------|---- [246,0] -90 -246 [128,0] -90 -128 [9,0] -90 -9 [0,9] 0 9 [0,128] 0 128 [0,246] 0 246  The points are the points that were converted from the peaks in Polar Coordinates. So now I need to draw all six of these lines and I have had no luck. Edit So I tried to change my code based off suggestions. This is what I came up with. function help(img, outfile, peaks, rho, theta) imshow(img); x0 = 1; xend = size(img,2); peaks_len=length(peaks); for i=1:peaks_len peak=peaks(i,:); r_ind=peak(1); t_ind=peak(2); r=rho(r_ind); th=theta(t_ind); %display([r,th,peak]); %// if a vertical line, then draw a vertical line centered at x = r % display([r, th]); if (th == 0) display('th=0'); display([1, size(img,1)]); line([r r], [1 size(img,1)], 'Color', 'green'); else %// Compute starting y coordinate y0 = abs((-cosd(th)/sind(th))*x0 + (r / sind(th)))+11;%-25; %// Compute ending y coordinate yend = abs((-cosd(th)/sind(th))*xend + (r / sind(th)))+11;%-25; display('y'); display([y0, yend]); display('x'); display([x0 xend]); %// Draw the line line([x0 xend], [y0 yend], 'Color', 'green'); end end end  I had to change from r==0 to th==0 because th=0 would give NAN errors when r was not 0. Based off the peaks, I then used that to get the data I needed to then calculate some values... but for some reason this isn't plotting well. If you notice the + 11 for both y values. I had to do that to get the lines to be where they need to. I have a feeling something else went wrong. I did change it so that my Rho values are all now positive.