When any sub-class of Stc is created, the constructor function
allows one or more AstroCoords elements to be stored within the Stc.
This function allows any one of these AstroCoords elements to be
retrieved. The format of the returned information is the same as
that used to pass the original information to the Stc constructor.
That is, the information is returned in a KeyMap structure
containing elements with one or more of the keys given by symbolic
constants AST__STCNAME, AST__STCVALUE, AST__STCERROR, AST__STCRES,
AST__STCSIZE and AST__STCPIXSZ.
If the coordinate system represented by the Stc has been changed
since it was created (for instance, by changing its System
attribute), then the sizes and positions in the returned KeyMap
will reflect the change in coordinate system.