Although a FrameSet may be used in place of its current Frame in most situations, it is sometimes convenient to have direct access to a specified Frame within it. This may be obtained using the astGetFrame function, as follows:
frame = astGetFrame( frameset, AST__BASE );
This would return a pointer (not a copy) to the base Frame within the
FrameSet. Note the use of AST__BASE
() as shorthand for the value of the
FrameSet's Base attribute, which gives the base Frame's index.
AST A Library for Handling World Coordinate Systems in Astronomy