[AstroPy] [pywcs] Unit question

Matt Hilton mattyowl at gmail.com
Tue Apr 12 18:47:26 EDT 2011


Hi folks, sorry for the delayed reply.

I maintain the astLib package, which actually contains more than just the wcs 
module, though I have no idea as to whether anyone actually uses the non-WCS 
parts bar me. It's basically just a collection of stuff that I developed 
through my PhD (and afterwards...) that I thought might be generally useful. 
During my PhD, pywcs was not available, hence the reason for the WCS module.

I have to confess that I've not actually looked at pywcs so far, and a lot of 
my own code (not surprisingly) uses the modules I made. I'm sure pywcs is 
great, but I've not felt the need to switch over just yet. I guess one good 
reason to switch would be handling distortion coeffs, which the version of 
wcslib used in WCSTools (which I wrapped) doesn't handle, but I haven't 
personally needed that yet. For sure, I could switch over bits of my code to 
use pywcs instead of astWCS, but it's a question of time and what the benefit 
would be (in terms of how it helps with getting my own research done).

> To the maintainers of the other wcs packages, what capabilities do you
> think pywcs is missing? Is there some way of merging the missing
> capabilities? Or is there a disagreement on the proper object model or
> interfaces? This seems like a good time to start such a discussion.
Since as I say I've yet to look at pywcs, I'm not exactly sure - but I think 
it would be nice to have a unified image class (perhaps some sort of 
pyfits/pywcs hybrid beast) with e.g. various clipping functions built in, for 
extracting postage stamps and the like.

Cheers,
Matt.

> On Apr 5, 2011, at 6:18 AM, Ole Streicher wrote:
> > Am 05.04.2011 09:33, schrieb Nico Nell:
> >> This can be done easily with astLib (http://astlib.sourceforge.net/).
> >> See function clipImageSectionWCS
> >> (http://astlib.sourceforge.net/docs/astLib/astLib.astImages-module.html#
> >> clipImageSectionWCS ).
> >> 
> >> Here is an example that I used to make clips from big GALEX fits
> >> files
> >> (http://casa.colorado.edu/~nell/cgit/cgit.cgi/pyscripts/tree/plotting/ga
> >> lex-clips.py )
> >> 
> >> Hopefully this makes things easier for you!
> > 
> > Thank you, Nico.
> > 
> > However, I started now using pywcs, and I would probably stick to that
> > unless I cannot use the problem with it.
> > 
> > I am still quite confused why there are parallel packages doing mainly
> > the same thing: astLib and astrolib are quite for the same purpose,
> > and
> > having both f.e. a wcslib wrapper. In my opinion, this parallel
> > development seems to me quite unnecessary and delays cooperation since
> > everyone historically uses his own preferred library. For different
> > programming languages, I could understand this, but I dont see a real
> > reason to have different pywcs modules.
> > 
> > Are there any attempts to unify the different approaches for
> > astro(python|lib)? What is the common opinion about the fragmentation
> > problem?
> 
> Actually, I'd like to help such a unification. WCS seems like an
> obvious place to start (it's not the only case though).
> 
> Mind you, I'm not adverse to people trying different approaches early
> on to see what works best, but after some point consolidation is
> usually a good idea.
> 
> So perhaps this is a good starting point for doing so with WCS. I
> haven't studied the details of this particular instance that much, but
> it certainly makes sense that one should be able to easily generate a
> new  WCS for a subarray. If pywcs can't do that yet, we should add
> that capability.
> 
> To the maintainers of the other wcs packages, what capabilities do you
> think pywcs is missing? Is there some way of merging the missing
> capabilities? Or is there a disagreement on the proper object model or
> interfaces? This seems like a good time to start such a discussion.
> 
> Perry
> 
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