Astrometric information can be split in two. For those data where there is no spatial component a position on the sky is all that is required. Data which has spatial axes may have a mapping between either pixel number or axis units and a celestial coordinate frame.
Astrometric information is handled in ADI by the class Pointing. It
has the following definition,
CHAR SYSTEM FK4, FK5 DOUBLE EQUINOX DOUBLE EPOCH DOUBLE RA,DEC,ROLL