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.
AST A Library for Handling World Coordinate Systems in Astronomy