Plotting lines in an efficient way.

Hi,

I'm detecting lines on an image by the Hough transform, when I use the function houghlines, it return me a struct that I called lines, containing the start and the end point of the lines detected, I'm plotting it by a foor loop:

 for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','red');
end

In this manner I obtain this result:

But plotting all the lines with the foor loop takes a lots of time.

In order to speed up, the process I have written the following code:

xy = [];
for k = 1:length(lines)
    point1 = lines(k).point1;
    point2 = lines(k).point2;
   xy = [xy; lines(k).point1; lines(k).point2];
end
plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','red');

But the result is:

How I have to modify the script in order to obtain, the same result of the first image?

Answer 1

[Jan]

It works without loops:

% Abbreviation of: [lines(:).point1; lines(:).point2] :
data = [lines.point1; lines.point2];
x    = data(:, 1:2:end);
y    = data(:, 2:2:end);
plot(x, y, 'LineWidth', 2, 'Color', 'r');

[KSSV]

The best solution.....+1

[Simone Cordella]

Thank you. It works well.

[Jan]

@KSSV: Thanks. Writing "+1" usually means, that one has voted for an answer. Currently my answer has 0 votes, so I assume, it is a general compliment. Thanks. I really appreciate the atmosphere of mutual cooperation in this forum.

I had tried 8 different versions, some contained reshape, transpose and cat, and NaNs also. Actually it would be interesting to see my worse approaches also as a tutorial, but this might look confusing in the forum.

Answer 2

[KSSV]

     xy = [];
    for k = 1:length(lines)
        point1 = [lines(k).point1 NaN];  % if throws error try  point1 = [lines(k).point1 ; NaN];
        point2 = [lines(k).point2 NaN]; %  if throws error try  point1 = [lines(k).point2 ; NaN];
       xy = [xy; point1; point2];
    end
    plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','red');

[Simone Cordella]

Thank you.