A CmpMap is a compound Mapping which allows two component Mappings (of any class) to be connected together to form a more complex Mapping. This connection may either be "in series" (where the first Mapping is used to transform the coordinates of each point and the second mapping is then applied to the result), or "in parallel" (where one Mapping transforms the earlier coordinates for each point and the second Mapping simultaneously transforms the later coordinates).
Since a CmpMap is itself a Mapping, it can be used as a component in forming further CmpMaps. Mappings of arbitrary complexity may be built from simple individual Mappings in this way.
AST A Library for Handling World Coordinate Systems in Astronomy