To be clear, GIFTI_Surface_Format.pdf does specify row-major
order, as is also used in NIFTI.  That does not mean the offsets
are along the bottom row.  The offsets are along the right column.

For an example, consider the FreeSurfer sample data, where the
matrix is not an identity.  There the offsets are in the right column,
and the bottom row is 0, 0, 0, 1, as it should always be.

NIFTI and GIFTI use the same format, as they should.

- rick