GIMIAS standard image orientation is LPS (SpatialOrientation::ITK_COORDINATE_ORIENTATION_RAI in ITK). This is the matrix that represents this orientation:
1 0 0 0 1 0 0 0 1
When an itk image is read from disk, it is automatically reoriented to GIMIAS standard orientation. For example:
- When reading an Analyze image with orientation RPI, it will be reoriented to RAI.
- When reading a DICOM image with orientation RAI, it will not be reoriented.
To check what are the possible orientations for Analyze image and how the conversion is done, you can check this header file: itkAnalyzeDbh.h