How to display a polygon and its centroid

Question

ISABELLE GUNDRUM 2022-3-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1665889-how-to-display-a-polygon-and-its-centroid

回答： yanqi liu 2022-3-8

I am using this code to draw polygons on an image, but I am unsure of how to later display the drawn polygon and centroid on the image. Any suggestions?

My code:

for k=1:3
    c{k} = zeros(1,3);
end
for k = 1:3
    tmp = input(['Press any key to draw Polygon # ' int2str(k) ': ']);
    close all, imshow(I), title(['Polygon # ' int2str(k)])
    h = drawpolygon;
    % The vertices of k-th polygon is recorded in polyin{k}
    polyin{k} = polyshape(h.Position); % create a polygon object
    [cx,cy] = centroid(polyin{k});
    c{k}(1:2) = round([cx cy],0);  % unit: pixels
    c{k}(3) = round(area(polyin{k}),0)*p2cm;   % unit: cm^2 
    if k==3
        tmp = input('Press any key to complete.')
    end
    disp(['Centroid of polygon: [' int2str([cx cy]) ']'])
    disp(['Area of polygon = ' int2str(c{k}(3)) 'cm^2'])
end

Thanks!

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Answer 1

Matt J 2022-3-7

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1665889-how-to-display-a-polygon-and-its-centroid#answer_912304

编辑：Matt J 2022-3-7

在 MATLAB Online 中打开

close all, imshow(I),
for k = 1:3
  
    title(['Polygon # ' int2str(k)]);
    
    h = drawpolygon;     
       wait(h);
    centroid=mean(h.Position);
    
    drawpoint('Position',centroid,'Label','Centroid');
    
    
end

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Answer 2

yanqi liu 2022-3-8

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1665889-how-to-display-a-polygon-and-its-centroid#answer_912489

在 MATLAB Online 中打开

I = imread('cameraman.tif');
p2cm = 1;
for k=1:3
    c{k} = zeros(1,3);
end
for k = 1:3
    tmp = input(['Press any key to draw Polygon # ' int2str(k) ': ']);
    close all, imshow(I), title(['Polygon # ' int2str(k)])
    h = drawpolygon;
    % The vertices of k-th polygon is recorded in polyin{k}
    polyin{k} = polyshape(h.Position); % create a polygon object
    [cx,cy] = centroid(polyin{k});
    c{k}(1:2) = round([cx cy],0);  % unit: pixels
    c{k}(3) = round(area(polyin{k}),0)*p2cm;   % unit: cm^2
    if k==3
        tmp = input('Press any key to complete.')
    end
    disp(['Centroid of polygon: [' int2str([cx cy]) ']'])
    disp(['Area of polygon = ' int2str(c{k}(3)) 'cm^2'])
    pts = [h.Position; h.Position(1,:)];
    delete(h);
    hold on; plot(pts(:,1), pts(:,2), 'r.-', 'LineWidth',3);
    plot(mean(pts(:,1)), mean(pts(:,2)), 'cp', 'MarkerFaceColor', 'c');
    hold off;
end