Find center of mass of parts of a matrix
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Hi, Let us say that I have a matrix as shown below:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/158429/image.png)
Then I apply a treshold to this matrix and am left with a region of interest. As such:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/158431/image.png)
How can I find the center of mass for this region of interest (using values from the corresponding indexes in the first matrix) and the location of this center of mass in the original matrix?
Thanks for any help
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Guillaume
il 28 Nov 2016
Modificato: Guillaume
il 28 Nov 2016
Well, go back to the definition of the centre of mass, which is just a weighted mean:
%inputs:
%originalmatrix: the original matrix
%binarisedmatrix = originalmatrix > threshold; %the thresholded matrix, a logical array
[rows, cols] = ndgrid(1:size(originalmatrix, 1), 1:size(originalmatrix, 2));
rowcentre = sum(rows(binarisedmatrix) .* originalmatrix(binarisedmatrix)) / sum(originalmatrix(binarisedmatrix));
colcentre = sum(cols(binarisedmatrix) .* originalmatrix(binarisedmatrix)) / sum(originalmatrix(binarisedmatrix));
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Guillaume
il 28 Nov 2016
Works fine for me:
originalmatrix = ones(10);
originalmatrix(4:7, 4:7) = 2 %semicolon missing for display
binarisedmatrix = originalmatrix > 1 %semicolon missing for display
[rows, cols] = ndgrid(1:size(originalmatrix, 1), 1:size(originalmatrix, 2));
rowcentre = sum(rows(binarisedmatrix) .* originalmatrix(binarisedmatrix)) / sum(originalmatrix(binarisedmatrix)) %semicolon missing for display
colcentre = sum(cols(binarisedmatrix) .* originalmatrix(binarisedmatrix)) / sum(originalmatrix(binarisedmatrix)) %semicolon missing for display
returns 5.5 for both rowcentre and colcentre
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