Remove centroid locations of objects that are too close

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Jason 2022-8-8

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https://ww2.mathworks.cn/matlabcentral/answers/1775905-remove-centroid-locations-of-objects-that-are-too-close

评论： Jason 2022-8-9

Hi, I have a list of centroid locations of spots in an image (xf, yf). The spots are randomly distributed. I want to remove the centroid locations that are too close to each other, or say within a distance of d. I've got to the following but not sure what to do next. Also is there a better way to do this ratrher than use loops?

%using a loop
M=[];
for j=1:length(xf)
    for i=1:length(xf)
        dx=xf(j)-xf(i);
        dy=yf(j)-yf(i);
        dr=sqrt(power(dx,2)+power(dy,2));
        M(j,1)=xf(j);
        M(j,2)=yf(j);
        M(j,3)=xf(i);
        M(j,4)=yf(i);
        M(j,5)=dr;    
    end    
end

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Matt J 2022-8-9

If two spots are less than d apart should both be removed? If not, by what criterion do you decide which spot remains?

Image Analyst 2022-8-9

To me it sounds like both are to be removed. This is easily done with pdist2.

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采纳的回答

Matt J 2022-8-9

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https://ww2.mathworks.cn/matlabcentral/answers/1775905-remove-centroid-locations-of-objects-that-are-too-close#answer_1023570

编辑：Matt J 2022-8-9

在 MATLAB Online 中打开

A=[xf(:) yf(:)];
D=pdist2(A,A);
D(D==0)=inf; %retroactive EDIT
keep = all(D>d,1);
xf=xf(keep);
yf=yf(keep);

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Jason 2022-8-9

Of course, its clear now, thankyou

Jason 2022-8-9

Just to add, when I had over 400 objects, akthough i do other operations, using the for loop took 110s.using the pdist2 approach took just under 2s. Remarkable!

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更多回答（1 个）

yanqi liu 2022-8-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1775905-remove-centroid-locations-of-objects-that-are-too-close#answer_1023405

在 MATLAB Online 中打开

yes，sir，may be use pdist2， such as

xf = rand(1, 10);
yf = rand(1, 10);
%using a loop
M=[];
for j=1:length(xf)
    for i=1:length(xf)
        dx=xf(j)-xf(i);
        dy=yf(j)-yf(i);
        dr=sqrt(power(dx,2)+power(dy,2));
        M(end+1,1)=xf(j);
        M(end,2)=yf(j);
        M(end,3)=xf(i);
        M(end,4)=yf(i);
        M(end,5)=dr;
    end
end
% second method
A=[xf(:) yf(:)];
B=pdist2(A,A);
C=B';
C=C(:);
isequal(M(:,end),C)
ans = logical
   1