MATLAB: Comparing two sets of coordinates

coordinate comparisonMATLABparticle comparison

I have two different datasets from two particle scans of a silicon wafer. Each dataset contains a number of x- and y-coordinates from particles found on the wafer. I now want to compare the pre dataset with the post dataset, and see if there are two particles that lie very close (within 30 um) and therefore must be the same.
Right now I am basically comparing each of the points from the pre measurment with all the points from the post measurement and see if any match. However, each dataset can contain several thousands of coordinates, which tend to make the process somewhat slow. Any suggestions on how to make this faster and smarter?
Kind regards Martin

Best Answer

Can you please show your code? The approach you describe works in less than a second (~ 0.6) on my computer, with n = 10000. Code:
% Make some data
n1 = 48;
n2 = 42;
x1 = rand(n1,1);
y1 = rand(n1,1);
x2 = rand(n2,1);
y2 = rand(n2,1);
% calculate all pairwise distances
changes = zeros(n1,n2);
for k = 1:n2
changes(:,k) = (x1-x2(k)).^2 + (y1-y2(k)).^2;
% find distances less than a given tolerance
tol = 0.001;
[j,k] = find(changes < tol);
Note that I'm using square (Euclidean) distance, to save on sqrt calculations.
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