Add a spectral coordinate conversion to a SpecMap


This function adds one of the standard spectral coordinate system conversions listed below to an existing SpecMap.

When a SpecMap is first created (using astSpecMap), it simply performs a unit (null) Mapping. By using astSpecAdd (repeatedly if necessary), one or more coordinate conversion steps may then be added, which the SpecMap will perform in sequence. This allows multi-step conversions between a variety of spectral coordinate systems to be assembled out of the building blocks provided by this class.

Normally, if a SpecMap s Invert attribute is zero (the default), then its forward transformation is performed by carrying out each of the individual coordinate conversions specified by astSpecAdd in the order given (i.e. with the most recently added conversion applied last).

This order is reversed if the SpecMap s Invert attribute is non-zero (or if the inverse transformation is requested by any other means) and each individual coordinate conversion is also replaced by its own inverse. This process inverts the overall effect of the SpecMap. In this case, the first conversion to be applied would be the inverse of the one most recently added.


void astSpecAdd( AstSpecMap this, const char cvt, int narg, const double args[] )


Pointer to the SpecMap.
Pointer to a null-terminated string which identifies the spectral coordinate conversion to be added to the SpecMap. See the " Available Conversions" section for details of those available.
The number of argument values supplied in the " args" array.
An array containing argument values for the spectral coordinate conversion. The number of arguments required, and hence the number of array elements used, depends on the conversion specified (see the " Available Conversions" section). This array is ignored and a NULL pointer may be supplied if no arguments are needed.


Available Conversions

The following strings (which are case-insensitive) may be supplied via the " cvt" parameter to indicate which spectral coordinate conversion is to be added to the SpecMap. Where arguments are needed by the conversion, they are listed in parentheses. Values for these arguments should be given, via the " args" array, in the order indicated. Units and argument names are described at the end of the list of conversions.

The units for the values processed by the above conversions are as follows:

The arguments used in the above conversions are as follows:

If the SpecMap is 3-dimensional, source positions are provided by the values supplied to inputs 2 and 3 of the SpecMap (which are simply copied to outputs 2 and 3). Note, usable values are still required for the RA and DEC arguments in order to define the " user-defined" reference frame used by USF2HL and HLF2US. However, AST__BAD can be supplied for RA and DEC if the user-defined reference frame is not required.