[AstroPy] Parameter 'origin' in WCS-methods

Erin Sheldon erin.sheldon@gmail....
Fri May 8 08:37:39 CDT 2009


On Fri, May 8, 2009 at 9:27 AM, Erin Sheldon <erin.sheldon@gmail.com> wrote:
> Try right click-> save as.
>
> Or just visit the directory and do the same on the links displayed there:
>
>  http://sdss.physics.nyu.edu/esheldon/python/code/

Hmm, the configuration of the web server seems to have changed with
our recent software update, it gives errors downloading .py files.
Sorry about that.

I tarred up the code in this file, which seems to download fine:

http://sdss.physics.nyu.edu/esheldon/python/code/astro_code.tar.gz


>
> cheers,
> Erin
>
> On Fri, May 8, 2009 at 9:24 AM, Martin Kuemmel <mkuemmel@eso.org> wrote:
>> Hi Erin,
>>
>> thanks for sharing this with us,
>> but at least I can not access the code (see below).
>>
>> Cheers,
>> Martin
>>
>> Erin Sheldon wrote:
>>>
>>> On Fri, May 8, 2009 at 8:48 AM, Michael Droettboom <mdroe@stsci.edu>
>>> wrote:
>>>>
>>>> The distortion table lookup is non-invertible (without doing some sort
>>>> of iterative approximation) -- so that's unimplemented.  There are some
>>>> good examples in Paper IV as to why it isn't really possible in a
>>>> general sense -- but it may be reasonable assuming that the lookup table
>>>> fits certain characteristics.
>>>>
>>>> SIP is only invertible if a set of inverted coefficients is provided in
>>>> the header, which we support but don't require.
>>>>
>>>> So it's more "difficult" than "impossible" -- it just isn't something
>>>> we've had an immediate need for here (which is primarily within the new
>>>> version of MultiDrizzle).
>>>
>>> I've got some wcs code that demonstrates how to do this:
>>>
>>> http://sdss.physics.nyu.edu/esheldon/python/code/
>>> wcsutil.py
>>>
>>> The sky2image method of the WCS class is relevant here.  By default it
>>> uses scipy.optimize.fsolve to get the inverse.
>>>
>>> Erin Sheldon
>>> Brookhaven National Laboratory
>>>
>>>> Mike
>>>>
>>>> Martin Kuemmel wrote:
>>>>>
>>>>> Thanks for explaining the 'origin'. Actually I had read
>>>>> these pages, but not carefully enough, obviously
>>>>>
>>>>> Next question:
>>>>> There is the method 'all_pix2sky(origin, *args)' to get sky coordinates,
>>>>> which includes "everything" (SIP, distortion, wcslib). There is no
>>>>> method 'all_sky2pix(origin, *args)'.
>>>>> Is it planned to have to implement this? Or is it difficult/impossible?
>>>>>
>>>>> Cheers,
>>>>> Martin
>>>>>
>>>> --
>>>> Michael Droettboom
>>>> Science Software Branch
>>>> Operations and Engineering Division
>>>> Space Telescope Science Institute
>>>> Operated by AURA for NASA
>>>>
>>>> _______________________________________________
>>>> AstroPy mailing list
>>>> AstroPy@scipy.org
>>>> http://mail.scipy.org/mailman/listinfo/astropy
>>>>
>>
>>
>> --
>> +----------------------------------------------------------------------+
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>


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