For each of the supported celestial coordinate systems, a SkyFrame can apply an optional shift of origin to create a coordinate system representing offsets within the celestial coordinate system from some specified reference point. This offset coordinate system can also be rotated to define new longitude and latitude axes. See attributes SkyRef, SkyRefIs, SkyRefP and AlignOffset.
All the coordinate values used by a SkyFrame are in radians. These may be formatted in more conventional ways for display by using AST_FORMAT.
AST A Library for Handling World Coordinate Systems in Astronomy