[AstroPy] fits coordinate system keyword
Paul Kuin
npkuin at gmail.com
Tue Oct 6 03:15:36 EDT 2015
It seems that WCS RADECSYS was not dropped then; it just ended up in the
standard in a different way. Probably to preserve backward compatibility to
old FITS files. It did throw me off, with just one letter difference! I
think there must be some old software that is still being used to create
fits files that do use RADECSYS. I was using it (not bothering to check
the standard all the time, - yes bad!) and I suspect that Swift UVOT
software uses it (which is built on the HEASARC FTOOLS - so that might use
it also). I'll bring it up in the UVOT group, but with the kind of very
limited software support that is left after 10 years of Swift mission, it
might not be possible to make the changes.
To get back to my original issue. I think this means the WCS keywords are a
historical set that is still supported, but non-standard. I also think
that getting a warning each time a file is opened is wrong.
In my software I'd like to disable that warning. I guess I'll need to have
a good look at the error handling in Astropy as I have somewhere another
warning pop up with loads of verbage, opening an ascii file. It actually
worked, just is very loud. I hope there is a way to get a different
response for errors and warnings to be used during testing and actual
use.
Thanks again for all the responses.
Paul Kuin
On Mon, Oct 5, 2015 at 11:03 PM, Tim Jenness <tim.jenness at gmail.com> wrote:
> 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
>>> > >
>>> > > _______________________________________________
>>> > > AstroPy mailing list
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>>> > <mailto:AstroPy at scipy.org <mailto:AstroPy at scipy.org>>
>>> > > https://mail.scipy.org/mailman/listinfo/astropy
>>> > >
>>> > >
>>> > >
>>> > >
>>> > > --
>>> > >
>>> > > * * * * * * * * 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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>>> >
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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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>>
>>
>>
>> --
>>
>> * * * * * * * * 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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--
* * * * * * * * 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.
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