[fitswcs] coordinates by table lookup

[William Pence]

Mark Calabretta wrote:
> 
> On Mon 2002/10/28 11:53:40 CDT, William Pence wrote
> in a message to: Mark Calabretta <Mark.Calabretta at atnf.CSIRO.AU>
> and copied to: fitswcs at NRAO.EDU
> 
> >Files on tape are not supported by this convention.  Even if there were a
> >way to refer to tape files, it would not be very useful within this context
> >if the tape is offline and there is no way for the software to automatically
> >access it.
> 
> Let me put it another way.  Suppose I have a collection of these files
> sitting on a disk and I want to archive them to tape (DLT say).  What
> happens to the file references?  Do I have to use a tape backup program
> which preserves the directory structure, e.g. tar (unix) or BACKUP (VMS)?
> Will this be portable?  (The "T" in FITS.)
> 
> Then what happens to URLs like '/local/user/wcsfile.fits' or
> 'ftp://nrao.edu/pub/wcsfile.fits' when I unload the tape elsewhere?
> 
> Or maybe I have to merge the files into one FITS file when the tape is
> written?

Those are all good questions.  I don't have any particularly insightful
answers other than to say that users have to be careful when moving data
sets from one location to another to preserve or update the file references.

Note that I'm not *recommending* that the WCS coordinate lookup extension be
put into a different file than the one that references it.  I'm simply
arguing that one should not *prohibit* that possibility, since it may be
appropriate in some circumstances.

Bill
-- 
____________________________________________________________________
Dr. William Pence                          pence at tetra.gsfc.nasa.gov
NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)     
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