MATLAB: Centroid of polyarea

centroidpolyarea

How to get a centroid of polyarea?
Here is my code.
Thanks.
figure, imshow('000445.png')
hold on
xy = [];
n = 0;
but = 1;
while but == 1
    [xi,yi,but] = ginput(1);
    plot(xi,yi,'r.')
    n = n+1;
    xy(:,n) = [xi;yi];
end
t = 1:n;
ts = 1: 0.1: n;
xys = spline(t,xy,ts);
plot(xys(1,:),xys(2,:),'r-');
A = polyarea(xys(1,:),xys(2,:));
plot(xys(1,:),xys(2,:),'r-');
title (['Area = ' num2str(A)]);
axis image
hold off

Best Answer

Hi,
I modified your first code becomes :
I = imread('peppers.png'); 
[r c o] = size(I);
imshow(I); hold on; 
xy = [];    
n = 0;    
but = 1; 
while but == 1 
    [xi, yi, but] = ginput(1); 
    plot(xi, yi, 'r.'); 
    n = n + 1; 
    xy(:, n) = [xi; yi]; 
end
t = 1 : n; 
ts = 1 : 0.1 : n; 
xys = spline(t, xy, ts); 
plot(xys(1,:), xys(2,:), 'r-');
A = polyarea(xys(1,:), xys(2,:));
plot(xys(1,:), xys(2,:), 'r-'); 
title (['Area = ' num2str(A)]); 
axis image 
%hold off
Then, I create my own code.
J = logical(zeros(r, c));
xcoor = floor(xys(1,:));
ycoor = floor(xys(2,:));
for x = 1 : numel(xcoor)    
    J(ycoor(x),xcoor(x)) = 1;    
end
J = imdilate(J,strel('square',20));
J = bwmorph(J,'thin',inf);
J = imfill(J,'holes');
stat = regionprops(J,'Centroid');
plot(stat.Centroid(1),stat.Centroid(2),'go',...
        'markerfacecolor','b')
And the result is :
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