[AstroPy] converting from proper motion in ra, dec to proper motion in galactic long, lat

Anne Archibald aarchiba@physics.mcgill...
Wed Jul 21 10:23:45 CDT 2010


On 21 July 2010 10:58, Wolfgang Kerzendorf <wkerzendorf@googlemail.com> wrote:
>  Hello,
>
> Does anyone know of something like this in any language? I also have
> errorbars that need converting.

I believe that SLALIB (for which Scott Ransom wrote python bindings)
can compute transformation matrices (i.e. the matrix of partial
derivatives) for its coordinate conversions; this should allow you to
convert proper motions. Error bars will take a little more work
because after matrix multiplication you need to convert a
non-axis-aligned error ellipse into some readily representable form.
Failing this, if you've got a good conversion library, you can just
compute the derivatives numerically (e.g.
(to_galactic(x+vx*t,y+vy*t)-to_galactic(x,y))/t for small but not too
small t).

Anne

> Cheers
>    Wolfgang
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