[AstroPy] fits coordinate system keyword
Thomas Robitaille
thomas.robitaille at gmail.com
Mon Oct 5 17:17:25 EDT 2015
I think there is a misunderstanding:
RADECSYS is not valid
RADESYS is valid
(note the extra C). We are not debating that RADESYS is valid - it is -
but the warning concerns the common mis-spelling of RADE*C*SYS. Does
this make sense?
Cheers,
Tom
Paul Kuin wrote:
> In the WCS II standard paper ( M. R. Calabretta and E. W. Greisen:
> Representations of celestial coordinates in FITS
> http://www.aanda.org/articles/aa/pdf/2002/45/aah3860.pdf) on page 1079
> the is a table defining some variables used. In particular 'a' is
> alternate version code 'blank or [A-Z]. In table 2 on page 1082, the
> definition is RADESYSa, meaning that valid versions are either RADESYS,
> RADESYSA, RADESYSB, ... , RADESYSZ.
>
> So it always was defined as a valid. Similar, EQUINOXa/. I've seen that
> mostly used as just EQUINOX. If the header has just one WCS block, or a
> preferred one, that is useful to have.
>
> Let's see what Bill Pence says. Maybe there were some changes after all.
>
>
>
> On Mon, Oct 5, 2015 at 8:34 PM, Thomas Robitaille
> <thomas.robitaille at gmail.com <mailto:thomas.robitaille at gmail.com>> wrote:
>
> Hi Paul,
>
> Just out of curiosity, was RADECSYS ever a keyword in the FITS standard,
> as opposed to RADESYS? (which is the currently valid keyword). If so, in
> what version of the standard?
>
> Cheers,
> Tom
>
> Paul Kuin wrote:
> > Actually, one of the basic tenets of FITS is to be completely backward
> > compatible, so any keyword that was valid in the past is valid now. So
> > that warning is also inaccurate. If it was standard, it still is, and
> > ever will be.
> >
> >
> >
> > On Mon, Oct 5, 2015 at 5:25 PM, Erik Bray <embray at stsci.edu
> <mailto:embray at stsci.edu>
> > <mailto:embray at stsci.edu <mailto:embray at stsci.edu>>> wrote:
> >
> > On 10/05/2015 12:17 PM, Paul Kuin wrote:
> >
> >
> >
> > I am getting very annoyed of the warning that keeps popping up
> >
> > WARNING: FITSFixedWarning: RADECSYS= 'FK5' / default
> > RADECSYS is non-standard, use RADESYSa. [astropy.wcs.wcs]
> >
> > I'm not sure when the FITS standard changed, but MOST legacy
> > fits files (I use)
> > will have the RADECSYS keyword. It works, and I do not see why
> > someone felt the
> > need to keep this warning being popped up all the time.
> >
> >
> > Probably as a warning to remind authors of new files that they
> > shouldn't be using that keyword. I don't know that it necessarily
> > needs to be displayed every time reading in a WCS except maybe to
> > head off cases of ambiguity. But I don't know this particular
> issue
> > well enough to be sure if the warning is appropriate in all
> cases or
> > not.
> >
> > I think that by default it should be off.
> >
> > Since you all probably think it should be there, I would
> like to
> > know how to
> > turn it off ? any suggestion on how to do that?
> >
> >
> > http://docs.astropy.org/en/stable/warnings.html
> >
> >
> > Erik
> >
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> >
> >
> >
> >
> > --
> >
> > * * * * * * * * http://www.mssl.ucl.ac.uk/~npmk/ * * * *
> > Dr. N.P.M. Kuin (n.kuin at ucl.ac.uk <mailto:n.kuin at ucl.ac.uk>
> <mailto:n.kuin at ucl.ac.uk <mailto:n.kuin at ucl.ac.uk>>)
> > phone +44-(0)1483 (prefix) -204927 (work)
> > mobile +44(0)7806985366 <tel:%2B44%280%297806985366> skype ID: npkuin
> > Mullard Space Science Laboratory – University College London –
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> >
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> --
>
> * * * * * * * * http://www.mssl.ucl.ac.uk/~npmk/ * * * *
> Dr. N.P.M. Kuin (n.kuin at ucl.ac.uk <mailto:n.kuin at ucl.ac.uk>)
> phone +44-(0)1483 (prefix) -204927 (work)
> mobile +44(0)7806985366 skype ID: npkuin
> Mullard Space Science Laboratory – University College London –
> Holmbury St Mary – Dorking – Surrey RH5 6NT– U.K.
>
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