The [3][1] element of the matrix used to rotate the subset of the
               Cartesian coordinates in the ATOM_SITE category identified in the
               STRUCT_SITE_GEN category to an orientation useful for
               visualizing the site. The conventions used in the rotation are
               described in _struct_site_view.details.
               |x'|                         |11 12 13| |x|
               |y'|reoriented Cartesian = |21 22 23| |y|Cartesian
               |z'|                         |31 32 33| |z|