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

[Perry Greenfield]

On May 2, 2012, at 4:42 PM, Tim Jenness wrote:

> On Wed, May 2, 2012 at 1:03 PM, Perry Greenfield <perry at stsci.edu>  
> wrote:
>> Are these necessarily exclusive approaches?
>
> AST was designed to handle mappings from different coordinate systems
> from the beginning to handle data pixel coordinates to WCS to graphic
> coordinates (and vice versa) in a transparent manner.
>
> The examples earlier in this thread are more based around conversion
> of a single value from one frame to another and there are many
> simplifications that are possible when that is done. A single galactic
> coordinate to the corresponding RA/Dec coordinate is a well understood
> conversion that never changes. AST will let you work out the world
> coordinates of a particular pixel in your image, or the pixel that
> corresponds to a particular WCS, or the position on the graphics
> plotting device corresponding to either the data pixel or the WCS
> coordinate. The transformation from RA/Dec to Galactic is all handled
> in a specialist SKY frame and you can actually do the simple
> translations by setting attributes in a Sky frame object without
> having to understand mappings and pixel coordinates (so easily
> wrappable).
>
I'm not sure I understand how this corresponds the two approaches  
(both could apply to one coordinate or multiple coordinates I think).

Isn't the issue whether frames are disconnected from specific  
coordinate values or not? If one designs it so that they are, what  
keeps one from making a class that bundles the system with one or more  
coordinate values so that it does know how to convert the value(s) to  
another system. I don't think one needs to design two parallel systems  
for that. The bundled representation simply contains an attribute  
which is a frame along with an attribute for its coordinates. But I  
could be missing the whole point :-)

>> (by the way, most of ast
>> links are slightly corrupted by appended closing parentheses
>> apparently).
>
> I think it depends on the mailer. gmail guesses (correctly) that the
> trailing parenthesis below is not part of the URL so it does work.
>
No, it's something weirder than that. I've sent all variants of urls  
with trailing parentheses and they all work as links in my mail reader.

Perry