An SlaMap is a specialised form of Mapping which can be used to represent a sequence of conversions between standard celestial (longitude, latitude) coordinate systems.
When an SlaMap is first created, it simply performs a unit (null) Mapping on a pair of coordinates. Using the astSlaAdd function, a series of coordinate conversion steps may then be added, selected from those provided by the SLALIB Positional Astronomy Library (Starlink User Note SUN/67). This allows multi-step conversions between a variety of celestial coordinate systems to be assembled out of the building blocks provided by SLALIB.
For details of the individual coordinate conversions available, see the description of the astSlaAdd function.
" printf" format specifiers identified by " %" symbols in
the normal way. If no initialisation is required, a zero-length string may be
supplied. " options" string contains " %" format specifiers,
then an optional list of additional arguments may follow it in order to supply
values to be substituted for these specifiers. The rules for supplying these are
identical to those for the astSet function (and for the C " printf" function).
The Nin and Nout attributes (number of input and output coordinates) for an SlaMap are both equal to 2. The first coordinate is the celestial longitude and the second coordinate is the celestial latitude. All coordinate values are in radians.
A null Object pointer (AST__NULL) will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.