I'm using the following script in order to calculate the Galactical Center (GC) position in galactical coordinates (in degrees) to celestial coordinates:
import healpy as hp
r = hp.Rotator(coord = ['G', 'C'], deg=True)
ri = hp.Rotator(coord = ['C', 'G'], deg=True)
gz, ga = 0., 0. # position of GC
gz_e, ga_e = r(gz, ga)
print gz_e, ga_e
zg, ag = ri(gz_e, ga_e)
print zg, ag
These are the results I get:
1.09730865695 -2.91715324734 # celestial
0.0 -1.57079632679 # back to galactical
First of all, the numbers are wrong in celestial as well as in galactical coordinates. There is a chance that I'm using the function wrong (which I hope), or something is wrong with the function itself. Does someone know what is going wrong?
Second: it seems, that I get the numbers in radian back, is that right?
deg refers only to the angles in rot, not to the Rotator itself. The Rotator needs theta (colatitude) and phi (longitude) in radians, see:
import healpy as hp
import numpy as np
r = hp.Rotator(coord = ['G', 'C'])
ri = hp.Rotator(coord = ['C', 'G'])
gz, ga = np.pi/2, 0. # position of GC
gz_e, ga_e = r(gz, ga)
print("Galactic center in Celestial Coordinates")
print(gz_e, ga_e)
zg, ag = ri(gz_e, ga_e)
print("Back to galactic coordinates")
print(zg, ag)
Output:
Galactic center in Celestial Coordinates
2.07582709512 -1.63354890767
Back to galactic coordinates
1.57079632679 -1.11022302489e-16