Finding distance between centers of circles by manually selecting muliple pairs

I am having trouble finding the correct distances from circle to circle. Is there a way to select manually which circles to measure the distances between? I would need to select multiple pairs and a circle can be in a pair more than once. Then be able to advance the program when finished. Not all circles are necessary to be selected. The circle finding itself works nicely.

I included the entire code. It grabs images from a file to analyze. Thank you.

directory = uigetdir;
files = dir(fullfile(directory, '*.bmp'));

for k = 1:length(files)
    fileName = files(k).name;
    fullFilePath = fullfile(directory, fileName);
    fprintf(1, 'Processing: %s\n', fullFilePath);
    rgb = imread(fullFilePath);
    rgb = imcrop(rgb,[950 0 400 750]);
    rgb = rgb2hsv(rgb);
    rgb = rgb(:,:,3);
    rgb = imadjust(rgb, [0.1 0.85]);
    %rgb = im2gray(rgb);
    rgb = adapthisteq(rgb);
    %crop
    
    rgb = im2bw(rgb,0.3);
    %binary conversion
    imshow(rgb)

    d = drawline;
    
    pos = d.Position;
    diffPos = diff(pos);
    diameter = hypot(diffPos(1),diffPos(2))
    
    [centers,radii] = imfindcircles(rgb,[10 400],'ObjectPolarity','dark','Sensitivity',0.8)
    
    imshow(rgb)
    h = viscircles(centers,radii);
    [centers,radii] = imfindcircles(rgb,[10 400],'ObjectPolarity','dark', ...
       'Sensitivity',0.8);
    
    length(centers)
    %
    delete(h)  % Delete previously drawn circles
    h = viscircles(centers,radii);
    
    [centers,radii] = imfindcircles(rgb,[10 400],'ObjectPolarity','dark', ...
             'Sensitivity',0.8,'Method','twostage');
    
    delete(h)
    h = viscircles(centers,radii);
    
    %hBright = viscircles(centersBright, radiiBright,'Color','b');
    
    h = viscircles(centers,radii);
    
    pix = 0.00001030927835;
    %calibration for pix to meter
    
    Yp(:) = centers(:,2);
    %need to do every other circle, This does distance between every one
    
    distance = abs(diff(Yp))
    %distance between center in pix
    
    Ydiff = distance*pix
    %distance between center in meters
    
    v = 0.142082
    % change this variable 'v' for every test run
    
    frequency = Ydiff/v
    % units 1/s 
    
    diameter = 0.00635;
    % units m 
    
    Strouhal = (frequency * diameter) / v
    %final strouhal number 
end

[KSSV]

Read about ginput.

Answer 1

[Sandeep Mishra]

Hi CLAYTON,

You can utilize the ‘ginput’ MATLAB function to manually select circles.

Below is an example code snippet demonstrating how to select multiple circles and store the pairs in a vector:

% Example Centers of different circles
centres = [300,350; 400,450; 100,150; 200,250] 

selectedPairs = [];
while true
    [x, y, button] = ginput(2);  
    
    % Exit the function on pressing ‘Enter’ button
    if isempty(x)  
        break;
    end
    
    % Finding nearest circles to the selected points
    idx1 = knnsearch(centers, [x(1), y(1)]);
    idx2 = knnsearch(centers, [x(2), y(2)]);
    
    selectedPairs = [selectedPairs; idx1, idx2];
end

Refer to the following MathWorks Documentation to learn more about ‘ginput’ function: https://www.mathworks.com/help/matlab/ref/ginput.html

I hope this helps you in resolving your query!