The pointer returned by AST_READ ()
could identify any class of Object--this is determined entirely by
the external data being read. If it is necessary to test for a
particular class (say a Frame), this may be done as follows using the
appropriate member of the AST_ISA<CLASS> family of functions:
LOGICAL OK
...
OK = AST_ISAFRAME( OBJECT, STATUS )
Note, however, that this will accept any Frame, so would be equally happy with a basic Frame or a SkyFrame. An alternative validation strategy would be to obtain the value of the Object's Class attribute and then test this character string, as follows:
OK = AST_GETC( OBJECT, 'Class', STATUS ) .EQ. 'Frame'
This would only accept a basic Frame and would reject a SkyFrame.
AST A Library for Handling World Coordinate Systems in Astronomy