MATLAB: Measure Line Segment Length Cross One Fixed Point

image analysisimage processingImage Processing Toolbox

I'd like to measure the shortest distance between two dark portion. The distance line segment should cross the red point on the image. The black and white background are logical values. The background matrix and the red point are known (attached as data.mat). I tried polyxpoly() but failed to use it. Any ideas? Thanks!

Best Answer

I already answered something very similar to this from you recently.

Why don't you try bwdist(). It will find the distance of every point to the closest background point. If you really need the distance that is not the shortest, but along some arbitrary line you draw, then you'll have to use improfile().

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MATLAB: How to find the nearest object to a reference point in binary image

It's trivial. Just use bwboundaries to get the list of (x,y) coordinates of the boundary and then put in a for loop, calculating the distance using the Pythagorean Theorem to get the boundary that is the closest. In the for loop, you can vectorize it and use min().

boundaries = bwboundaries(binaryImage);
overallMinDistance = inf;
for b = 1 : length(boundaries)
   thisBoundaryX = boundaries{b}(:, 1);
   thisBoundaryY = boundaries{b}(:, 2);
   distances = sqrt((thisBoundaryX - refx).^2 + (thisBoundaryY - refy).^2);
   [minDistance, indexOfMin] = min(distances);
   if minDistance < overallMinDistance
      % This boundary is the closer one.
.............you finish the rest - it's easy.
end

MATLAB: Trouble using regionprops and imdistline

Use bwmorph with the 'endpoints' option to identify the end points and then use the distance formula (i.e. hypot()) to calculate distance between endpoints.

If this is a skeleton, use regionprops' 'perimeter' option and divide it by two. The problem with using area is that it calculates city-block distance rather than quasi-euclidean and will not give you a good approximation to length. See the description here.

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MATLAB: How to find the nearest object to a reference point in binary image

MATLAB: Trouble using regionprops and imdistline

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