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Line orientation in 3D from centroid and Euler angles

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matnewbie
matnewbie 2018-6-19
评论： Saurabh Patel 2018-9-20
I used the regionprops3 function to detect centroid and Euler angles of cylinders of the same size in 3D space. Now I want to obtain the 3D coordinates of a line (of given length, representing the axis of the cylinders) passing through the centroid and oriented according to the three Euler angles. What kind of coordinate transformation should I consider?

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Matt J
Matt J 2018-6-19
编辑：Matt J 2018-6-19
I think you'd be better off using regionprops3 to extract the Eigenvalues and Eigenvectors properties of the cylinders, instead of the Orientation property (which I assume you are using now). The eigenvector corresponding to the largest eigenvalue should give you the direction vector of the long axis of the cylinder directly.
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Matt J
Matt J 2018-6-19
编辑：Matt J 2018-6-19
Well, as I said, the eigenvector corresponding to the largest eigenvalue is the direction vector. So, you have it already from
regionprops3(yourImage, 'Centroid','EigenVectors','EigenValues')
One thing to note. I believe the EigenVectors are the rows of the matrix given in the output of regionprops3, not the columns.
Saurabh Patel
Saurabh Patel 2018-9-20
I think eigenvectors are still the columns of eigenvector matrix but they are in image coordinates i.e. (row,col,page) and not in (x,y,z).
For (x,y,z) space, I think we need to represent it as {eigenvector(2,1), eigenvector(1,1), eigenvector(3,1)} for the major principal direction.

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