Calculate radius from scatter plot

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yonatan s 2020-6-22

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编辑： yonatan s 2020-7-9

Hi,

I need to calculate the radius of a circle, ignoring all surrounding particles (image attached). The circle itself consists of many particles (over 100,000). Note that the center of the circle is not at the origin.

Thanks.

EDIT: here is how I solved it:

posn=normal(poscm); %poscm is the coordinates matrix
[k,edges]=histcounts(posn,1e5);
[~,imaxk]=max(k);
R=edges(imaxk+find(k(imaxk:end)==0,1)); %find the first zero value after the maximum

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yonatan s 2020-6-23

It's not perfect, but it seems isoutlier is the right approach.

pdist consumes too much memory.

I tried using some image processing tools, the problem is that axes change when transforming the plot to an image.

Thanks.

Adam Danz 2020-6-23

If you're still looking for a solution, attach the fig file containing the data, or attach a mat file containing the (x,y) coordinates.

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回答（3 个）

Matt J 2020-6-22

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You could try using clusterdata to find the big concentration of points. Then minboundcircle from the File Exchange to get the radius,

https://www.mathworks.com/matlabcentral/fileexchange/34767-a-suite-of-minimal-bounding-objects

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yonatan s 2020-6-23

I have too many particles for that, it requires a lot of memory

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darova 2020-6-23

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在 MATLAB Online 中打开

Try density function hist3

r = rand(500,1)/5;
t = rand(500,1)*2*pi;
x = [rand(50,1); r.*cos(t)+0.5]; 
y = [rand(50,1); r.*sin(t)+0.5];
n = 20;
k = hist3([x y],[n n]);
k(k<2) = nan;
pcolor((0:n-1)/n,(0:n-1)/n,k)
hold on
plot(x,y,'.r')
hold off