As for a SkyFrame, a SpecFrame is a Frame () and also a
Mapping (
), so it inherits all the properties and
behaviour of these two ancestral classes. When used as a Mapping, a
SpecFrame implements a unit transformation, exactly like a basic Frame
(
) or a UnitMap, so this aspect of its
behaviour is not of great importance.
When used as a Frame, however, a SpecFrame represents a wide range of
different 1-dimensional coordinate system which can be used to describe
positions within a spectrum. The options available largely mirror those
described in the FITS-WCS paper III Representations of spectral
coordinates in FITS (Greisen, Valdes, Calabretta & Allen).
AST A Library for Handling World Coordinate Systems in Astronomy