[AstroPy] fits coordinate system keyword
Tim Jenness
tim.jenness at gmail.com
Mon Oct 5 18:03:44 EDT 2015
RADECSYS is a very common historic header that was used before support was
added for multiple WCS definitions in a single header. I think it was
dropped before the official paper II standard was published was was part of
the initial draft:
See e.g. http://www.adass.org/adass/proceedings/adass99/P1-29/
--
Tim Jenness
On Mon, Oct 5, 2015 at 2:47 PM, Paul Kuin <npkuin at gmail.com> wrote:
> That is so. You're absolutely right! I'm so sorry! I did not catch that
> one.
>
> That is probably an error that sneeked into the FITS headers from Swift.
> Perhaps its a Heasarc thing, but somehow I think its a bug.
>
> Thank you all for helping with this.
>
> Paul
>
> On Mon, Oct 5, 2015 at 10:17 PM, Thomas Robitaille <
> thomas.robitaille at gmail.com> wrote:
>
>> 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 –
>> > > Holmbury St Mary – Dorking – Surrey RH5 6NT– U.K.
>> > >
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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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>> > AstroPy at scipy.org
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>
>
>
> --
>
> * * * * * * * * http://www.mssl.ucl.ac.uk/~npmk/ * * * *
> Dr. N.P.M. Kuin (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.
>
> _______________________________________________
> AstroPy mailing list
> AstroPy at scipy.org
> https://mail.scipy.org/mailman/listinfo/astropy
>
>
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