Before we start, it is worth taking a quick look at the Mapping class as a whole and some of the sub-classes it contains:
Mapping CmpMap DssMap IntraMap LutMap MathMap MatrixMap PermMap SlaMap SpecMap UnitMap WcsMap ZoomMap Frame <various types of Frame>
The Frame sub-class has been separated out here because it is covered
in detail in . We start by looking at the parent
class, Mapping.
AST does not provide a function to create a basic Mapping (i.e. the AST_MAPPING constructor does not exist). This is because the Mapping class itself is ``virtual'' and basic Mappings are of no use in themselves. The Mapping class serves simply to contain the various specialised Mappings that exist. However, it provides more than just a convenient heading for them because it bestows all classes of Mapping with common properties (e.g. attributes) and behaviour. By examining the Mapping class, we are therefore examining the things that all other Mappings have in common.
AST A Library for Handling World Coordinate Systems in Astronomy