[AstroPy] Problem running pywcs example

Michael Droettboom mdroe@stsci....
Thu Aug 19 08:23:48 CDT 2010


On 08/18/2010 03:56 PM, Peter Erwin wrote:
> Hi Mike,
>
> Thanks for the quick reply!
>
> It looks like what happened is that *was* an earlier version of pywcs hiding
> in /Users/erwin/lib/python [as opposed to
> /Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6 ,
> which is where pywcs 1.9 got installed].  Possibly it got installed as part of
> an earlier installation of stsci_python ...
>
> Anyway, I nuked the earlier installation, and now pywcs seems to work.
>
>
> Am I missing something, or does the documentation for pywcs mention anywhere what
> "sky coordinates" actually means (i.e., allowed formats, types, order, etc.?).
>    

The order is described in the wcs_sky2pix docstring:

"""

Either two or three arguments may be provided.

        * 2 arguments: An /N/ x /naxis/ array of /x/- and
          /y/-coordinates, and an /origin/.
        * 3 arguments: 2 one-dimensional arrays of /x/ and /y/
          coordinates, and an /origin/.

"""

As for types, it may be any numeric type (and the underlying 
calculations are performed in doubles).

> (From my experiments so far, I'm guessing that the output of WCS.wcs_pix2sky()
> for a single pair of pixel coordinates is [[Dec, RA]], with both in decimal degrees...?)
>    
The fact that it's decimal degrees is somewhat buried (in the 
description of the lower-level wcslib functions.)  I will move this 
information up to the higher-level functions -- and that should make it 
into the next version of the docs.

Mike
> cheers,
>
> Peter
>
> On Aug 18, 2010, at 9:04 PM, Michael Droettboom wrote:
>
>    
>> This problem occurs due to a version incompatibility between pyfits and
>> pywcs.
>>
>> Recent versions of pyfits (2.3 and later) were refactored to no longer
>> support numarray.  pywcs required a change to be compatible with this
>> (this change first appeared in pywcs 1.8).
>>
>> Given the versions you list, you should be ok -- however it seems that
>> you are not running the version of pywcs you think you are.  Perhaps you
>> need to blitz the installation directory (in your case,
>> /Users/erwin/lib/python/pywcs) and reinstall.
>>
>> Mike
>>
>> On 08/18/2010 02:40 PM, Peter Erwin wrote:
>>      
>>> Hi,
>>>
>>> I decided to check out pywcs (in part because using Pyraf to get pixel values from
>>> RA,Dec pairs seemed to be overkill, and wcwcstran was failing to work for SDSS
>>> images with declinations close to zero).
>>>
>>> The installation ("python setup.py install") seemd to go fine, but I ran into the following when I tried
>>> running the example from http://stsdas.stsci.edu/astrolib/pywcs/examples.html
>>>
>>> <<begin quote>>
>>> In [164]: hdulist = pyfits.open("pgc1905g_94-220.fits")   # this is an SDSS g-band image
>>> In [165]: wcs = pywcs.WCS(hdulist[0].header)
>>> ---------------------------------------------------------------------------
>>> AttributeError                            Traceback (most recent call last)
>>>
>>> /Users/erwin/Documents/Working/ESO_observing/WFI/targets/pgc1905_808/<ipython console>   in<module>()
>>>
>>> /Users/erwin/lib/python/pywcs/pywcs.py in __init__(self, header, fobj, key, minerr, relax, naxis)
>>>      176             self.naxis = wcsprm.naxis
>>>      177
>>> -->   178             det2im = self._read_det2im_kw(header, fobj)
>>>      179             cpdis = self._read_distortion_kw(
>>>      180                 header, fobj, key=key,dist='CPDIS', err=minerr)
>>>
>>> /Users/erwin/lib/python/pywcs/pywcs.py in _read_det2im_kw(self, header, fobj)
>>>      278         cdelt = [1.,1.]
>>>      279
>>> -->   280         if not isinstance(fobj, pyfits.NP_pyfits.HDUList):
>>>      281             return (None, None)
>>>      282
>>>
>>> AttributeError: 'module' object has no attribute 'NP_pyfits'
>>> <<end quote>>
>>>
>>> My system is: MacBook Pro (2009) running Mac OS 10.6.4, Python 2.6.5 (standard framework install
>>> from python.org) via ipython 0.10
>>> numpy 1.4.1
>>> pyfits 2.3.1 [same problem occurred for pyfits 2.2.2; I
>>> pywcs v1.9-4.4.4
>>>
>>> (All packages are installed inside the framework directory, *except* for pyfits, which installed in
>>> ~/lib/python )
>>>
>>> Any suggestions?
>>>
>>>     -- Peter
>>>
>>> =============================================================
>>> Peter Erwin                   Max-Planck-Insitute for Extraterrestrial
>>> erwin@mpe.mpg.de              Physics, Giessenbachstrasse
>>> tel. +49 (0)89 30000 3695     85748 Garching, Germany
>>> fax  +49 (0)89 30000 3495     http://www.mpe.mpg.de/~erwin
>>>
>>>
>>>
>>> _______________________________________________
>>> AstroPy mailing list
>>> AstroPy@scipy.org
>>> http://mail.scipy.org/mailman/listinfo/astropy
>>>
>>>        
>>
>> -- 
>> Michael Droettboom
>> Science Software Branch
>> Space Telescope Science Institute
>> Baltimore, Maryland, USA
>>
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy@scipy.org
>> http://mail.scipy.org/mailman/listinfo/astropy
>>      
> =============================================================
> Peter Erwin                   Max-Planck-Insitute for Extraterrestrial
> erwin@mpe.mpg.de              Physics, Giessenbachstrasse
> tel. +49 (0)89 30000 3695     85748 Garching, Germany
> fax  +49 (0)89 30000 3495     http://www.mpe.mpg.de/~erwin
>
>
>
> _______________________________________________
> AstroPy mailing list
> AstroPy@scipy.org
> http://mail.scipy.org/mailman/listinfo/astropy
>    


-- 
Michael Droettboom
Science Software Branch
Space Telescope Science Institute
Baltimore, Maryland, USA

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