MATLAB: I want to find out the x,y co-ordinates of the minor and major axis of an elliptical shaped portion in the Image.

image analysisimage processingImage Processing Toolboxmajoraxislengthminoraxislength;regionprops

I have a binary image, in that I have a shape similar to an ellipse(this ellipse is distorted a bit). I want to find out the major and minor axes of that ellipse. I have tried using regionprops. C=regionprops(H,'ConvexHull','MinorAxisLength','MajorAxisLength'); It is of no help as it gives me only the length of it and not the co-ordinates of those points that after being joined gives us the minor and major axes respectively. It would be really nice if you could help me find the endpoints of those axes.

Best Answer

Use bwboundaries() to get the perimeter (x,y) coordinates, then use the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_fit_an_ellipse_or_other_shape_to_a_set_of_XY_data.3F

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MATLAB: Major axis and minor axis

regionprops() to get the centroid and orientation (angle). After that it becomes straight trig. The axes length is R, compute R*cos(theta), R*sin(theta), and center those displacements on the centroid.

MATLAB: Drawing the major and minor axis of an elliptical object in Matlab

Here's a start:

   ctr = regionprops(keeperBlobsImage,'centroid');
   theta = regionprops(keeperBlobsImage,'orientation');
   xMajor = ctr(1)  +  [ -1 +1 ] * measurements(1)*cosd(theta)/2;
   yMajor = ctr(2)  +  [ -1 +1 ] * measurements(1)*sind(theta)/2;
   line(xMajor,yMajor);

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MATLAB: Major axis and minor axis

MATLAB: Drawing the major and minor axis of an elliptical object in Matlab

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