[fitswcs] WCS documents

[Arnold Rots]

I strongly support what Steve wrote.  An unambiguous standard for the
purpose of data transport is called for and that standard ought to be
as simple as possible, while at the same time providing _all_
necessary information.  That requires that the standard be as general
as possible.  An one-pixel axis is clearly a special case of a
multi-pixel axis - hence there should be no need to treat it any
differently, bearing in mind that the number of pixels, after all, is
provided.

The degenerate axis has served many of us well and I don't see any
reason to abandon it.  It requires no great effort to make display
_soft_ware recognize and deal with such axes.  If it wasn't designed
to do that, maybe it's time to think about putting that generalization
in.  One might also argue that the use of degenerate axes makes it
easier on various general purpose tools by not treating the one-pixel
axes as special cases.

I am opposed to ad-hoc solutions and see no reason to complicate the
picture by introducing WCSAXES.

  - Arnold

Steve Allen wrote:
> 
> On Tue 2001-09-18T11:09:03 -0400, Bob Hanisch hath writ:
> > Sure.  A colleague was trying to compare VLA and HST (WFPC) data.  The VLA
> > data had been processed with AIPS, HST data with IRAF and IDL.  The HST data
> > had been rotated and resampled by another colleague, in IDL I think, and it
> > was not clear if the WCS had been updated properly.  In addition, the VLA
> > data uses the CDELT/CROTA WCS convention, and HST data uses the CD matrix.
> 
> And the upshot is that almost all of these FITS files are going to
> need to be updated by specialized conversion software in order to
> conform to whatever becomes the final WCS standard.
> 
> We could try to decide the issue based on not breaking compatibility
> with existing software that uses interim and/or local standards, but
> if we do that we risk the nasty situation of trying to resolve why
> your application is more important than my application, and his, and
> hers, etc.  I prefer to choose the clearest means of expressing the
> information for transport.  Then the individual application owners can
> create suitable translation algorithms.
> 
> The original FITS papers supplied the example of degenerate axes.
> Other than for the sake of compatibility with some existing
> applications what are reasons not to follow that example?
> 
> --
> Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
> sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
> PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
> 

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Arnold H. Rots                                Chandra X-ray 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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