updated wcs papers

[Arnold Rots]

I had hoped to come with a more comprehensive list, but that carries
the danger that it will never happen, so I'll just provide the
comments as they come up.  Two in this message.

On the subject of primary and secondary axis descriptions, the paper
does not say explicitly that one cannot have secondary descriptions
without a primary (i.e., say, CTYPE1P without there being a CTYPE1).
I don't think that is intended and it may be a good idea to say
explicitly that one can have a primary axis description without any
secondaries, but no secondary without a primary.
On the same subject, it may be good to clarify explicitly whether it
is allowed to have duplications (say, one has CTYPE1, CTYPE1A,
CTYPE1B, CTYPE1C, CTYPE1P, CTYPE1Q; and it so happens that
CTYPE1=CTYPE1C=CTYPE1C).  I must admit that I shudder at the thought,
but others may want to attach special meanings to particular secondary
identifiers (P for physical, for instance) which could force one into
these duplications.

The second is RADECSYS.  I think we need more values.  Chandra is
going to churn out FITS files with RADECSYS='ICRS'; FK5 is certainly
not appropriate anymore.

  - Arnold

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Arnold H. Rots                                         AXAF Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 81                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head-cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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