How to fill contours in a contour matrix

Yeah, I know, I could use contourf, but I want to draw the contours generated by contourc on another plot. What I need help with is how to close the contours, in particular those at the edge of the data.

If you run this code, you will see what I mean. How to properly close the contour at the lower left corner and the one at the top.

data = [ ...
    9 9 9 9 1 1 1 1 1 1 1 1 1 1 1 1; ...
    9 9 9 9 1 1 1 1 1 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 9 9 9 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 9 9 9 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 1 9 1 1 1 1 1 1 1; ...
    1 1 1 1 1 1 1 9 9 9 1 1 1 1 1 1; ...
    1 1 1 1 1 1 9 9 9 9 9 1 1 1 1 1];

figure(1)
clf
subplot(2,2,1)
imagesc(data)
set(gca, 'YDir', 'normal', 'XLim', [1 12], 'YLim', [1 12]);

subplot(2,2,2)
C = contourf(data, 1);

subplot(2,2,3)
kdx = 1;
while (1)
    l = C(1,kdx);
    n = C(2,kdx);
    x = C(1,(kdx+1):(kdx+n-1));
    y = C(2,(kdx+1):(kdx+n-1));
    plot(x, y); hold on
    patch(x, y, l);
    kdx = kdx + n + 1;
    if (kdx > size(C,2))
        break;
    end
end
set(gca, 'XLim', [1 12], 'YLim', [1 12]);

Thanks so much Bill

[Image Analyst]

What really do you want to do? It's not clear what your ultimate goal is. I'm wondering why you're dealing with contour and patch rather than just the image directly. I don't want you to just say "I want to close the contours" -- I want to know why you think you need to do that and maybe we can come up with a better approach. If you get the desired output image (of which, I'm not clear what that might be), then what would you do with it?

[Otis]

I am using contourc to generate contours in a set of data. I want to take those contours and draw them over top an area in another plot of a completely different set of data. I will adjust the x,y values accordingly, and I want to have the option to draw them either as lines or as filled patches. As you can see from my simple example, either the contour matrix output by contourc/contourf does not contain enough information to draw the contours properly (subplot(2,2,3) does not match subplot(2,2,2)) or I'm missing something.

[Otis]

I had to punt on this problem because of time, I needed to get something done today. But I still want to understand how the contour matrix, C, computed by contourc, is used to draw the boxes in subplot(2,2,2) and not subplot(2,2,3)

>> disp(C')
    1.0000    1.0000
       NaN       NaN
    5.0000   11.0000
   11.5000   12.0000
   11.0000   11.5000
   10.5000   11.0000
   10.0000   10.5000
    9.5000   10.0000
    9.0000    9.5000
    8.5000   10.0000
    8.0000   10.5000
    7.5000   11.0000
    7.0000   11.5000
    6.5000   12.0000
    5.0000   11.0000
   10.0000    6.5000
   10.5000    6.0000
   10.5000    5.0000
   10.0000    4.5000
    9.0000    4.5000
    8.0000    4.5000
    7.5000    5.0000
    7.5000    6.0000
    8.0000    6.5000
    9.0000    6.5000
   10.0000    6.5000
    5.0000    6.0000
    1.0000    2.5000
    2.0000    2.5000
    3.0000    2.5000
    4.0000    2.5000
    4.5000    2.0000
    4.5000    1.0000

Answer 1

[Image Analyst]

I'd do it as an image. See http://blogs.mathworks.com/steve/2009/02/18/image-overlay-using-transparency/ If you only have one level for the contour, as your one example shows (just the "red" level) then you can threshold and get a binary image and overlay the binary image as Steve shows in his blog. If you want outlines, you can use bwboundaries() in the Image Processing Toolbox and then use plot() to plot the boundaries as graphical lines in the overlay above the image.