Distance between object and point

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r_com3 2019-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/497659-distance-between-object-and-point

回答： Image Analyst 2019-12-21

Hello,

In the image below I need to find a nearest point to each of the corners (green marks) of the red bounding box for each object. This point must belong to the object (white shape).

So for each object, I need to locate 4 points, which are closest to the green corners of the bounding around the object.

Anyone has idea how to perform it?

Thanks in advane for any help

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r_com3 2019-12-21

I found a PixelList in regionprops.

If i get it right, in PixelList i have coordinates of each pixel belonging to object.

Is checking distance for each pixel and corner of bounding box a good idea?

Thanks for help

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Answer 1

Image Analyst 2019-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/497659-distance-between-object-and-point#answer_407321

在 MATLAB Online 中打开

No. Use bwboundaries() instead. It will be faster since you have far fewer points to check the distance from. If you have x and y upper/lower left/right corner point locations, then do something like (untested):

boundaries = bwboundaries(binaryImage);
for k = 1 : length(boundaries)
    thisBoundary = boundaries{k};
    x = thisBoundary(:, 2);
    y = thisBoundary(:, 1);
    
    % Find distances to upper left point (xul, yul)
    distances = sqrt((xul - x).^2 + (yul - y).^2);
    [minDistance, indexOfMinDistance] = min(distances)
    % Save the upper left boundary point as xb(k, 1) and yb(k, 1)
    xb(k, 1) = x(indexOfMinDistance);
    yb(k, 1) = y(indexOfMinDistance);
    
    % Now repeat for upper right.
    % Find distances to upper right point (xur, yur)
    distances = sqrt((xur - x).^2 + (yur - y).^2);
    [minDistance, indexOfMinDistance] = min(distances)
    % Save the upper left boundary point as xb(k, 2) and yb(k, 2)
    xb(k, 2) = x(indexOfMinDistance);
    yb(k, 2) = y(indexOfMinDistance);
    
    % Now repeat for lower right.
    % Find distances to lower right point (xlr, ylr)
    distances = sqrt((xlr - x).^2 + (ylr - y).^2);
    [minDistance, indexOfMinDistance] = min(distances)
    % Save the lower right boundary point as xb(k, 3) and yb(k, 3)
    xb(k, 3) = x(indexOfMinDistance);
    yb(k, 3) = y(indexOfMinDistance);
    
    % Now repeat for lower left.
    % Find distances to lower left point (xll, yll)
    distances = sqrt((xll - x).^2 + (yll - y).^2);
    [minDistance, indexOfMinDistance] = min(distances)
    % Save the lower left boundary point as xb(k, 2) and yb(k, 4)
    xb(k, 4) = x(indexOfMinDistance);
    yb(k, 4) = y(indexOfMinDistance);
end