[AstroPy] numpy; bulk coordinate conversions

Victoria G. Laidler laidler at stsci.edu
Thu May 11 16:01:53 CDT 2006

Andrew Jaffe wrote:

>Actually, I wasn't talking about offline storage, really -- I was  
>really talking
>nted to know what sort of array/list/etc to use within python. I was  
>already planning on using the routines from coord.position, but it  
>seems that there's likely a lot of overhead in storing many  
>individual position objects, especially when I'll want to do the same  
>conversions on each of them.
Hi Andrew,

I would give it a try, anyway - I've worked with a catalog of 10**4 
objects without
difficulty, although I was doing angular separation calculations rather than
coordinate transformations.

I used a simple list of Positions, if I recall correctly,
since I was just looping through them. Or maybe a dictionary, with object id
as key and Position as value.

Eventually we do want to either:

   - enhance Position so it can internally hold an array of positions, 
all with the same
equinox, coordinate system, etc; or,

   - define a new Catalog object, which would be an array of positions, 
all with the
same equinox, coordinate system, etc; and had a similar set of methods 
as Position
that would operate on the whole catalog -- as well as some methods that 
only make
sense on Catalogs.

The latter makes more sense to me, but there may be some software 
reasons to opt for the former.

What else are you going to do with these positions, besides transform 
them? Maybe a
real use case will help settle this question.


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