def teme_to_itrs_mat(time):
# Sidereal time, rotates from ITRS to mean equinox
# Use 1982 model for consistency with Vallado et al (2006)
# http://www.celestrak.com/publications/aiaa/2006-6753/AIAA-2006-6753.pdf
gst = erfa.gmst82(*get_jd12(time, 'ut1'))
# Polar Motion
# Do not include TIO locator s' because it is not used in Vallado 2006
xp, yp = get_polar_motion(time)
pmmat = erfa.pom00(xp, yp, 0)
# rotation matrix
# c2tcio expects a GCRS->CIRS matrix as it's first argument.
# Here, we just set that to an I-matrix, because we're already
# in TEME and the difference between TEME and CIRS is just the
# rotation by the sidereal time rather than the Earth Rotation Angle
return erfa.c2tcio(np.eye(3), gst, pmmat)
def _gmst82_angle(obstime):
"""
Universal Time to Greenwich mean sidereal time (IAU 1982 model).
Parameters
----------
obstime : Time
time at which the polar motion should be calculated.
Returns
-------
float
Greenwich mean sidereal time (radians)
"""
# Get GMST82 angle in rad
# noinspection PyArgumentList
gmst82 = erfa.gmst82(*get_jd12(obstime, "ut1")) * u.rad
return gmst82
# Mean obliquity
EPSA = erfa.obl80(DJMJD0, TT)
# Build the rotation matrix
RN = erfa.numat(EPSA, DPSI, DEPS)
# Combine the matrices: PN = N x P
RNPB = erfa.rxr(RN, RP)
print("NPB matrix, equinox based:")
pprint(RNPB)
# Equation of the equinoxes, including nutation correction
EE = erfa.eqeq94(DJMJD0, TT) + DDP80 * math.cos(EPSA)
# Greenwich apparent sidereal time (IAU 1982/1994).
GST = erfa.anp(erfa.gmst82(DJMJD0 + DATE, TUT) + EE)
print("GST = %.17f radians" % GST)
print(" = %.17f degrees" % math.degrees(GST))
print(" = %s%dd%dm%d.%ds" % erfa.a2af(6, GST))
print(" = %s%dh%dm%d.%ds" % erfa.a2tf(6, GST))
# Form celestial-terrestrial matrix (no polar motion yet).
##RC2TI = erfa.cr(RNPB)
##RC2TI = erfa.rz(GST, RC2TI)
RC2TI = erfa.rz(GST, RNPB)
print("celestial to terrestrial matrix (no polar motion)")
pprint(RC2TI)
# Polar motion matrix (TIRS->ITRS, IERS 1996).
RPOM = erfa.ir()
RPOM = erfa.rx(-YP, RPOM)
# Mean obliquity
EPSA = erfa.obl80(DJMJD0, TT)
# Build the rotation matrix
RN = erfa.numat(EPSA, DPSI, DEPS)
# Combine the matrices: PN = N x P
RNPB = erfa.rxr(RN, RP)
print("NPB matrix, equinox based:")
pprint(RNPB)
# Equation of the equinoxes, including nutation correction
EE = erfa.eqeq94(DJMJD0, TT) + DDP80 * math.cos(EPSA)
# Greenwich apparent sidereal time (IAU 1982/1994).
GST = erfa.anp(erfa.gmst82(DJMJD0+DATE, TUT) + EE)
print("GST = %.17f radians"%GST)
print(" = %.17f degrees"%math.degrees(GST))
print(" = %s%dd%dm%d.%ds"%erfa.a2af(6, GST))
print(" = %s%dh%dm%d.%ds"%erfa.a2tf(6, GST))
# Form celestial-terrestrial matrix (no polar motion yet).
##RC2TI = erfa.cr(RNPB)
##RC2TI = erfa.rz(GST, RC2TI)
RC2TI = erfa.rz(GST, RNPB)
print("celestial to terrestrial matrix (no polar motion)")
pprint(RC2TI)
# Polar motion matrix (TIRS->ITRS, IERS 1996).
RPOM = erfa.ir()
RPOM = erfa.rx(-YP, RPOM)