The SkyFrame constructor function is particularly simple and a SkyFrame with default attributes is created as follows:
INCLUDE 'AST_PAR'
INTEGER SKYFRAME, STATUS
STATUS = 0
...
SKYFRAME = AST_SKYFRAME( ' ', STATUS )
Such a SkyFrame would represent the default celestial coordinate
system which, at present, is the ICRS system (the default was "FK5(J2000)"
in versions of AST prior to 3.0).
AST A Library for Handling World Coordinate Systems in Astronomy