[AstroPy] Parameter 'origin' in WCS-methods

Erin Sheldon erin.sheldon@gmail....
Fri May 8 08:27:14 CDT 2009


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/

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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