[AstroPy] [astropy-dev] Coordinates subpackage - request for help
Thu Nov 15 07:04:16 CST 2012
I uploaded a script here
I made it a gist, since it sounds like it may need to be refined.
On Thu, Nov 15, 2012 at 3:29 AM, David Berry <firstname.lastname@example.org>wrote:
> On 14 November 2012 22:01, Demitri Muna <email@example.com> wrote:
> > Hi,
> > We are in the process of testing the new astropy coordinates package.
> One test that I think would be useful is this (which Tom also mentioned):
> > * generate 1000 ra/dec J2000 random points on the sky
> > * convert them to, in steps,
> > - galactic
> > - B1950
> > - ecliptic
> > - equatorial J2000
> > Can someone do this in IDL? The result should be
> > * the file containing 1000 points
> > * the resulting points at the end of the conversions
> > * the IDL script
> > The aim is to write a script using the coordinates package and see if
> there are any discrepancies. We will add this to the testing suite.
> > I thought I'd cc the astropy list as I'm sure there are lots of people
> who are proficient in IDL and can probably do this pretty quickly.
> 1) Different conversion algorithms are always (or nearly always) going
> to produce different answers. So do you have a target accuracy for the
> astropy coordinates package? Do you want arcseconds accuracy or
> milli-arcsecond accuracy? The more accuracy you want, the more
> sophisticated the algorithms need to be.
> 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
> 3) You include ecliptic in the list. Does the coordinates package
> support ecliptic? I could not see it in the code.
> 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)?
> 5) Was the omission of ICRS intentional?
> 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.
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