[AstroPy] API question: Instantiating of time/coord and similar

James Turner jturner at gemini.edu
Wed May 2 18:56:57 EDT 2012

> Obviously from my point of view there is 20 years of
> experience in coordinate handling inside the pyast library and it
> would be great to leverage that some how. I assume there is a goal of
> only relying on numpy as the only non-pure python library so pyast
> would not be acceptable but you could design a system that used AST
> internally and switched it out at a later date when you wanted to go
> pure python.

That sounds pretty sensible to me and good input for those of us
working with co-ordinates in Python. Perhaps a year ago, I and a
couple of other people (including Perry) separately recognized some
important concepts for handling co-ordinates that are missing from
FITS but that will be needed in Python software, such as combining
mappings as I think Tim is describing. After a little discussion,
Paul Hirst pointed me to AST, which had already incorporated the
same ideas N years previously :-). However, there is indeed some
reluctance to pull another C library into the equation, for multiple
good reasons. Although there's bound to be some variation on how to
approach things, the problems are sufficiently non-trivial that a
working model and/or prior experience seem valuable things to have...

Not sure where things stand regarding the GPL etc. though? I think
the decision was to use BSD in AstroPy. (If you reply just to this
question I'd suggest changing the subject.)



> Even if you don't want to use AST I feel strongly that the idea of
> separating frames from mappings and allowing frames and mappings to be
> stacked together is incredibly powerful. It's a very flexible approach
> that allows specific class knowledge to be added incrementally; time
> support was not in the original AST release and neither was support
> for spectral coordinates or IFUs.
> If you want to see AST in use, the new version of DS9 relies entirely
> upon AST for coordinate plotting and transformations.
>> P.S.: I should also apologize as this was meant for the astropy-dev list and not for astropy (but I guess everyone who's on dev is on astropy as well).
> I'll sign up. I had missed the dev list.

More information about the AstroPy mailing list