# Why are the spherical and cartesian galactic coordinates in the ATNF Pulsar Catalogue different?

I am trying to relate Galactic Latitude (b) and Longitude (l) (spherical coordinates) to galactic cartesian x,y,z coordinates in the ATNF pulsar catalog.

This query shows some sample data with G_l, G_b, XX, YY, and ZZ; excerpt:

------------------------------------------------------------------
#     NAME                     Gl     Gb     ZZ     XX     YY
(deg)  (deg)  (kpc)  (kpc)  (kpc)
------------------------------------------------------------------
1     J0002+6216    cwp+17     117.33 -0.07  -0.00  0.00   8.50
2     J0006+1834    cnt96      108.17 -42.98 -0.59  0.60   8.70
3     J0007+7303    aaa+09c    119.66 10.46  0.25   1.20   9.18


The description of the variables from the ATNF documentation are as follows:

GL:          Galactic longitude (degrees)
GB:          Galactic latitude (degrees)
[...]
ZZ:          Distance from the Galactic plane, based on Dist
XX:          X-Distance in X-Y-Z Galactic coordinate system (kpc)
YY:          Y-Distance in X-Y-Z Galactic coordinate system (kpc)


My understanding is that these variables should be related by the following equations:

• tan(G_L) = YY/XX
• tan(G_b) = XX/ZZ

However, when I test this assumption my calculated values are very different: I have tried exploring the possibility that the x,y,z coordinate system may be oriented differently than I expect, but I can find no orientation that yields similar results for G_l or G_b: Where could I have gone wrong? I feel like I am losing my mind not being able to convert these with simple trig.

From a heliocentric point of view (U, V, W) = (8.5 - YY, XX, ZZ). Then $\tan{l} = V / U$ and $\tan{b} = W / \sqrt{U^2 + V^2}$ as you'd expect.
• Aha, thank you! A few notes in case anyone runs into similar troubles: 1. my YY and XX column labels are swapped (oops). 2. This answer unconventionally maps yxz to uvw, more typically it is xyz to uvw 3. The last equation for G_b should be tan(b) = 90 - W/sqrt(u^2+v^2) Mar 30, 2018 at 14:52