User input from clicking on a position on a diagram/image

Question

Stuart 2012-3-11

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Hello,

I was wondering whether it was possible to get a use an image to get an input for matlab.

Take a football pitch for example. Would it be possible to get a birds eye image of a pitch and split it up into a grid, the user pics a particular square in the grid which then returns a x,y co-ordinate to matlab.

Its sort of possible using VBA in excel, however I'm not as handy with Matlab as I am excel.

Thanks for your time.

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Answer 1

Image Analyst 2012-3-12

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Yes. Use ginput() to get a point. Then convert that x,y point into calibrated units using your knowledge of how many pixels correspond to how many real world units (such as meters).

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RAGAV K 2012-7-9

在 MATLAB Online 中打开

I did the same, below is the piece of code:

   axis ij;
   axis manual;
   [m n] = size(d1);  %%d1 is the image which I want to display
   axis([0 m 0 n])
   imshow(d1);
   coordinates_input = round(ginput(1));

But when I checked the value of coordinates_input it was [25.5000,91.5000];

How do I change this so that I get pixel position in whole numbers?

Image Analyst 2012-7-9

在 MATLAB Online 中打开

That will happen if your image doesn't have unit magnification. For example if it's magnified so that one image pixel takes up 9 screen pixels, you can click "in the middle of a pixel" and the coordinates will give you that fractional location. Rounding, as you've done, seems like a reasonable way to return the pixel closest to where the user clicked. See this demo to understand:

d1 = rand(40);
axis ij;
axis manual;
[m n] = size(d1);  %%d1 is the image which I want to display
axis([0 m 0 n])
imshow(d1);
zoom(8)
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0.5 1 0.5]);
coordinates_input = ginput(1)
row = round(coordinates_input(2));
column = round(coordinates_input(1));
fprintf('You clicked on coordinates (row, column) = (%f, %f)\nWhich is the pixel in row %d, column %d\n', ...
  coordinates_input(1), coordinates_input(2), row, column);