Calculate PatientOrientation

[FlMart]

Hi everyone!

When converting a NIFTI to a valid DICOM, header fields have to be set and it would be nice to have a function to calculate a DICOM's PatientOrientation attribute given its ImageOrientationPatient attribute. Alternatively, according to your documentation, an affine matrix could also be used as input.

I haven't found such a method in Nibabel yet but I figured it would fit quite well alongside the nibabel.orientations methods. Is this something that you would consider worth implementing? Am I missing an already existing way of creating this string?

[effigies]

I think you probably want aff2axcodes. Unless I'm misunderstanding...

[FlMart]

As far as I understood it, the PatientOrientation requires multiple letters if the vector lies right between two axes, so with RAS labeling, a vector of x = [1,1,0] should return RA, which does not seem to be case for me. With the following code, what I get is ('R', 'A', 'S') while I would expect ('RI', 'RA', 'PS'):

aff1 = np.asarray([
    [1, 1, 0, 0],
    [0, 1, -1, 0],
    [-1, 0, 1, 0],
    [0, 0, 0, 1],
])
print(nib.aff2axcodes(aff1, (("L", "R"), ("P", "A"), ("I", "S"))))

Edit: There is a resource for C++ code that seems to provide the functionality that I want along with some better explanation.