How does this function "regionprops" to find the orientation of any object?

How does this function "regionprops" to find the orientation of any object?

[Simone conigliaro]

hi, I would like to ask to you what function is possible to use to find orientation in 3D. i used "regionprops "to obtain orientation in 2D. what function do you suggest? please answer it.

[Image Analyst]

regionprops() is the function I would suggest also.

[Simone conigliaro]

thanks for your answer but regionprops(orientation) is no possibile to use for orientation of blobs 3D. it is excellent for 2/d. another advice? thanks

[Simone conigliaro]

'Orientation' — Scalar; the angle (in degrees ranging from -90 to 90 degrees) between the x-axis and the major axis of the ellipse that has the same second-moments as the region. This property is supported only for 2-D input label matrices.

[Simone conigliaro]

do you know another property that is supported for 3D input label matrix? many thanks

[Image Analyst]

Use principal components analysis, pca().

[Simone conigliaro]

thanks. could you write how i calculate it? if is possible the matlab code because i have no idea how to calculate.

many thanks

[Image Analyst]

You'd use [y, x, z] = find(binaryImage) and then pass them into pca(). I don't have a demo for exactly that, but I'm attaching a demo of using pca to determine axes for a color gamut, for whatever that's worth.

[Simone conigliaro]

thanks for your replay. i have another question to ask you. i would like to know what is the method that regionprops label the object? because i used this function to get centroid and volume(sum voxel for each blob)but i don't understand this aspect. thank you very much

Answer 1

[David Legland]

Hi Marian,

the code is in the regionprops function, you can access it via "edit regionprops", and checking the "ComputeEllipseParams" function.

The principle is to compute the inertia ellipse of a shape. It is obtained by computing normalised centered moments. The matrix of Inertia is obtained from the normalised moments of order 2 : Ixx, Ixy, and Iyy. By extracting eigen values and eigen vectors of the inertia matrix, it is possible to obtain the direction of the first eigen vector, that is converted into angle.

[Image Analyst]

Please mark as Accepted if it answers your question.

[marian wagdy]

OK, thanks.

Answer 2

[Image Analyst]

It fits the blob to an ellipse and then gets the angle of the major axis of the ellipse from the horizontal. Note: the major axis of the fitted ellipse is not the farthest distance between two points in the blob.

[marian wagdy]

Yes, I know this, but I want to know the details of this function by using the mathematical equations,and the code

[marian wagdy]

thanks for reply