A SpecFrame is a specialised form of one-dimensional Frame which represents
various coordinate systems used to describe positions within an electro-magnetic
spectrum. The particular coordinate system to be used is specified by setting
’ s System attribute (the default is wavelength) qualified, as
necessary, by other attributes such as the rest frequency, the standard of rest, the
epoch of observation, etc (see the description of the System attribute for
By setting a value for thr SpecOrigin attribute, a SpecFrame can be made to represent offsets from a given spectral position, rather than absolute
"format specifiers identified by
"symbols in the normal way. If no initialisation is required, a zero-length string may be supplied.
"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
"System=VELO, RestFreq=1.0E15, StdOfRest=LSRK
") axis with rest frequency 1.0E15 Hz (about 3000 Angstroms), measured in the kinematic Local Standard of Rest (
"). Since the source position has not been specified (using attributes RefRA and RefDec), it will only be possible to align this SpecFrame with other SpecFrames which are also measured in the LSRK standard of rest.
When conversion between two SpecFrames is requested (as when supplying SpecFrames to astConvert), account will be taken of the nature of the spectral coordinate systems they represent, together with any qualifying rest frequency, standard of rest, epoch values, etc. The AlignSystem and AlignStdOfRest attributes will also be taken into account. The results will therefore fully reflect the relationship between positions measured in the two systems. In addition, any difference in the Unit attributes of the two systems will also be taken into account.
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.