This stores the parameters necessary for the computation of
real world coordinates from the sampling grid along this axis and reverse.
This encapsulates the WCS parameters separately for each Characterisation axis.
the main WCS coefficients as defined in the FITS standard, with one exception:
the ctype parameter is split into projection and coordinate name, in order to be more explicit. Here all parameters are explicit, but we can have a generalised class with arrays of coeeficients .
It specializes the class Mapping.
It contains the following attributes: