Hi there,
I have a small question about the NeuroImaging plugin for Nifti generation,
We noticed that the NIFTI generated by Orthanc seems to be in the LAS orientation, that’s not a bug the orientation vector correctly indicate this orientation simply my question is about the choice of the orientation.
It seems that the NIFTI format is by default RAS
"The most visible improvement of the nifti format over the previous analyze format is the ability to unambiguously store information orientation. The file standard assumes that the voxel coordinates refer to the center of each voxel, rather than at any of its corners. The world coordinate system is assumed to be ras: +x is Right, +y is Anterior and +z is Superior, which is precisely different than the coordinate system used in analyze, which is las. "
The RAS orientation is also the choice of nii babel " We are using the term “RAS” to mean that the axes are (in terms of the subject): left to Right; posterior to Anterior; and inferior to Superior, respectively. Although it is common to call this convention “RAS”, it is not quite universal, because some use “R”, “A” and “S” in “RAS” to mean that the axes starts on the right, anterior, superior of the subject, rather than ending on the right, anterior, superior. In other words, they would use “RAS” to refer to a coordinate system we would call “LPI”. To be safe, we’ll call our interpretation of the RAS convention “RAS+”, meaning that Right, Anterior, Superior are all positive values on these axes."
https://nipy.org/nibabel/coordinate_systems.html
But this has been also a source of confusion see the discussion here about RAS vs LAS orientation : [Insight-users] Nifti vs Dicom orientation
I just wanted to know, if nifti has a real standard orientation and why the neuro imaging plugin prefered LAS over RAS orientation ?
At the end the impact is not major as using the orientation vector you can reorient the image in any direction you want but I want just to understand what would be a default choice to try to have similar orientation accross all nifti librairies.
Best regards,
Salim