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Referring to the Base and Current Frames  

It is often necessary to refer to the base and current Frames ([*]) within a FrameSet, but it can be cumbersome having to obtain their indices from the Base and Current attributes on each occasion. To make this easier, two parameter constants, AST__BASE and AST__CURRENT, are defined in the AST_PAR include file and may be used to represent the indices of the base and current Frames respectively. They may be used whenever a Frame index is required.

For example, when adding a new Frame to a FrameSet ([*]), you could use the following to indicate that the new Frame is related to the existing current Frame, whatever its index happens to be:

      INTEGER FRAME, MAPPING

      ...

      CALL AST_ADDFRAME( FRAMESET, AST__CURRENT, MAPPING, FRAME, STATUS )

Of course, the Frame you added would then become the new current Frame.



next up previous
Next: Using a FrameSet as a Mapping
Up: Coordinate System Networks (FrameSets)
Previous: The Base and Current Frames

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
30th April 2003
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2003 Central Laboratory of the Research Councils