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Displaying Objects

Let us now return to the ZoomMap that we created earlier ([*]) and examine what it's made of. There is a routine for doing this, called AST_SHOW, which is provided mainly for looking at Objects while you are debugging programs.

If you consult the description of AST_SHOW in [*], you will find that it takes a pointer to an Object as its argument (in addition to the usual STATUS argument). Although we have only a ZoomMap pointer available, fortunately this is not a problem. If you refer to the brief class hierarchy described above ([*]), you will see that a ZoomMap is an Object, albeit a specialised one, so it inherits the properties of all Objects and can be substituted wherever an Object is required. We can therefore pass our ZoomMap pointer directly to AST_SHOW, as follows:

      CALL AST_SHOW( ZOOMMAP, STATUS )

The output from this will appear on the standard output stream and should look like the following:

Begin ZoomMap
   Nin = 2
IsA Mapping
   Zoom = 5
End ZoomMap

Here, the ``Begin'' and ``End'' lines mark the beginning and end of the ZoomMap, while the values 2 and 5 are simply the values we supplied to initialise it ([*]). These have been given simple names to make them easy to refer to.

The line in the middle which says ``IsA Mapping'' is a dividing line between the two values. It indicates that the ``Nin'' value is a property shared by all Mappings, so the ZoomMap has inherited this from its parent class (Mapping). The ``Zoom'' value, however, is specific to a ZoomMap and isn't shared by other kinds of Mappings.


next up previous 264
Next: Getting Attribute Values
Up: An AST Object Primer
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AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council