A TimeMap is a specialised form of 1-dimensional Mapping which can be used to represent a sequence of conversions between standard time coordinate systems.
When a TimeMap is first created, it simply performs a unit (null) Mapping. Using the astTimeAdd function, a series of coordinate conversion steps may then be added. This allows multi-step conversions between a variety of time coordinate systems to be assembled out of a set of building blocks.
For details of the individual coordinate conversions available, see the description of the astTimeAdd function.
AST A Library for Handling World Coordinate Systems in Astronomy