[AstroPy] comments on coordinate system and wcs packages

Victoria G. Laidler laidler at stsci.edu
Fri May 4 14:32:35 EDT 2012

I would just like to chime in that I think the IFU use case 
is going to become increasingly important, and I would like 
to see an IFU example worked out in the 
documentation/rationale for whatever approaches are considered.

I'd also like to call out the question of whether a 
mapping/transform produces a tuple of floats, or a more 
complex object that knows its contents and units, and has 
fields that can be accessed to get the floats. The latter is 
the approach we took in Astrolib Coords, and I think it is 
more versatile, not *too* much more verbose, and *much* more 
readable to write, say,

x = eq_to_galactic(y)
x.ra, x.dec

than to write
x = eq_to_galactic(y)
x[0], x[1] #danger will robinson
ra, dec = x #ok, but why not do the former?

This circles back to the original question of user 
interfaces, and touches on Perry's point about units.


On 05/04/2012 02:22 PM, James Turner wrote:
>> First, addressing AST. There seem to be two separate thoughts on this;
>> one is that AST should be adopted as is (made the underlying basis for
>> an astropy library) and the second is that it's interface should be
>> considered for any library constructed for astropy (but that the AST
>> implementation itself need not be adopted).
> Well, I think there's a third thought that we should study the AST
> design, talk to Tim&  David and heavily borrow any useful concepts :-).
> It seems unlikely that the interface would be identical in Python. I
> did also have one or two questions myself about why AST does things
> certain ways, compared with what I'd had in mind previously.
> What you say about keeping things like units&  fitting separate
> certainly makes sense and indeed we have to solve the problem of
> adding the necessary fitting code first.
> It would be good to sync up on where things stand at some point; I've
> had to put this on the back burner for a while and it sounds like in
> the meantime you've made a bit of progress and Wolfgang and others
> have been thinking about co-ordinate handling in AstroPy. My
> assumption was that I'd quickly have to implement something as simple
> as possible by myself (or maybe with Nadia) when I get back to it (I
> hope in the next couple of months), but if there's already something
> to build on, that might be a lot better :-). As I mentioned, I had
> this in mind as a possible AstroPy sprint (in addition to Erik's list
> of problems to solve).
> Cheers,
> James.
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