[fitswcs] Status of WCS negotiations

[William Pence]

Don Wells wrote:

> (2) MULTIPLE-WCS: It appears to me that there is a requirement to
> support multiple WCS descriptions of the same data object. I recommend
> that we do this by appending a character code [A-Z] to the WCS
> keywords for secondary descriptions; the keywords without the
> character would be the default operational ones. This notation would
> require reducing the number of axes supported by the WCS keywords from
> 999 to 99. If any of you have alternative ideas for multiple-WCS,
> please post them to 'fitswcs'; if you support my suggestion, post
> about that. If the people on this mailing list could agree on this
> notational convention, my bet is that the rest of the FITS community
> would agree too.

This gets trickly when one considers the analogous WCS keywords that are
needed when the 'image' is stored as a pixel/event list in a table or as
2D vector within a single cell of a table.  See the suggested keyword
names in table 8 of the current draft (? August 28, 1996).  In many of
these cases the index number represents the column number, not the axis
dimension, and in these cases one would certainly want to continue to
support 3 digit column numbers.  Thus in these cases, instead of
*appending* a character code [A-Z] we would instead *replace* the last
letter of the current 5-letter keyword root names with the character
code [A-Z].  Examples:

       Primary Array             Pixel list
       -------------             ----------
        CTYPEiii                  TCTYPnnn
        CTYPEAii                  TCTYAnnn
        CTYPEBii                  TCTYBnnn
____________________________________________________________________
Dr. William Pence                          pence at tetra.gsfc.nasa.gov
NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)     
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