[AstroPy] comments on coordinate system and wcs packages

[James Turner]

> 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.