[AstroPy] [astropy-dev] Coordinates subpackage - request for help

Thomas Robitaille thomas.robitaille@gmail....
Thu Nov 15 11:27:28 CST 2012

>> 2) Why does it need to be IDL? It's proprietary software, so many
>> people will not use it. There are many tools in many freely available
>> languages for creating tables of corresponding positions in different
>> coordinate systems.   For instance, I could create such a table
>> quickly using PyAST, which since we're talking Python seems an obvious
>> choice.
> This is purely for testing purposes and not meant to be released for use by anyone. I specifically chose IDL since the libraries are well-trusted and well-tested by the community. I think a selling feature would be to show that our code compares favorably with what people trust.

I think it would be great to have a PyAST version of the testing
script in addition to the IDL one. I think it's fair to say that
people trust AST (possibly even more than the IDL routines!).

As for accuracy, I think we should aim for <0.01" initially - the
rationale being that 1" accuracy won't be very useful for e.g. HST
observations. In the long term, I would argue that microsecond
accuracy would be desirable.


>> 3) You include ecliptic in the list. Does the coordinates package
>> support ecliptic? I could not see it in the code.
> Erik implemented the actual systems; I'll let him address that.
>> 4) Your list of coordinate systems starts at " ra/dec J2000" and ends
>> at "equatorial J2000" - are you making a distinction between these?
>> And I presume you mean FK5 J2000 (there is a common usage of "J2000
>> RA/Dec" which uses the mean dynamical equator and equinox of the J2000
>> epoch as reference, which is different to FK5)?
> Admittedly, the list was hastily written. Basically any routines for any systems available, we want to test.
>> 5) Was the omission of ICRS intentional?
> See above.
>> 6) No mention of the epoch of observation. As I mentioned in another
>> message you need to specify the epoch of observation, to be able to
>> convert accurately to and from an FK4 RA/Dec system (which I presume
>> is what you mean by "B1950"). Strictly, you also need the epoch of
>> observation when converting between FK5 and ICRS, albeit the
>> dependency on the epoch is much weaker.
>> 7) You need to specify an equinox for the ecliptic coordinates.
> You are correct (see "hastily written" :). The request should have included a note to randomly generate any additional information needed.
> As for the output, it would be ideal to generate the random points and save that as a file. Another script could then convert those points into various systems and either write out each result as a separate file or convert from one system to another, and write the results out to a new file.
> Thanks again for the help!
> Cheers,
> Demitri
> _________________________________________
> Demitri Muna
> Center for Cosmology and Particle Physics
> New York University
> http://scicoder.org

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