def test_polar_motion_unsupported_dates():
msg = r'Tried to get polar motions for times {} IERS.*'
with pytest.warns(AstropyWarning, match=msg.format('before')):
get_polar_motion(Time('1900-01-01'))
with pytest.warns(AstropyWarning, match=msg.format('after')):
get_polar_motion(Time('2100-01-01'))
def cirs_to_gcrs(time):
# compute the polar motion p-matrix
xp, yp = get_polar_motion(time)
sp = erfa.sp00(*get_jd12(time, "tt"))
pmmat = erfa.pom00(xp, yp, sp)
# now determine the Earth Rotation Angle for the input obstime
# era00 accepts UT1, so we convert if need be
era = erfa.era00(*get_jd12(time, "ut1"))
# c2tcio expects a GCRS->CIRS matrix, but we just set that to an I-matrix
# because we're already in CIRS
return erfa.c2tcio(np.eye(3), era, pmmat)
def _polar_mot_matrix(obstime):
"""
Form the matrix of polar motion for a given date, IAU 2000.
The matrix operates in the sense V(TRS) = rpom * V(CIP), meaning that it is the final rotation when computing the
pointing direction to a celestial source.
Parameters
----------
obstime : Time
time at which the polar motion should be calculated.
Returns
-------
3x3 rotation matrix due to polar motion
"""
# compute the polar motion p-matrix
xp, yp = get_polar_motion(obstime)
sp = erfa.sp00(*get_jd12(obstime, 'tt'))
polar_mot_mat = erfa.pom00(xp, yp, sp)
return polar_mot_mat
from astropy.coordinates.builtin_frames.utils import get_polar_motion
from astropy.time import Time
import astropy.units as u
import numpy as np
import matplotlib.pyplot as plt
t = Time('2010-01-01T00:00') + np.linspace(0, 10 * 365, 5000) * u.day
xp, yp = get_polar_motion(t)
fig = plt.figure(figsize=(6, 5))
ax = fig.add_subplot(111, projection='3d')
ax.plot(np.rad2deg(xp) * 3600, np.rad2deg(yp) * 3600, t.mjd)
ax.set_xlabel(r'$x_p \,\,/\,\, \mathrm{as}$')
ax.set_ylabel(r'$y_p \,\,/\,\, \mathrm{as}$')
years = np.arange(2010, 2021, 1)
ticks = Time([f'{y}-01-01T00:00' for y in years])
ax.set_zticks(ticks.mjd)
ax.set_zticklabels(years.astype(str))
ax.view_init(elev=20, azim=45)
fig.tight_layout()
fig.savefig('build/polar_motion.pdf')