def test_appendix_c_conversion_from_TEME_to_ITRF():
rTEME = array([5094.18016210, 6127.64465950, 6380.34453270])
vTEME = array([-4.746131487, 0.785818041, 5.531931288])
vTEME = vTEME * 24.0 * 60.0 * 60.0 # km/s to km/day
jd_utc = julian_date(2004, 4, 6, 7, 51, 28.386)
d_ut1 = -0.439961
jd_ut1 = jd_utc + d_ut1 / 86400.0
xp = -0.140682 * arcsecond
yp = 0.333309 * arcsecond
rITRF, vITRF = TEME_to_ITRF(jd_ut1, rTEME, vTEME, xp, yp)
epsilon = 5e-8 # Why not 1e-8, which would match all of their digits?
assert abs(-1033.47938300 - rITRF[0]) < epsilon
assert abs(+7901.29527540 - rITRF[1]) < epsilon
assert abs(+6380.35659580 - rITRF[2]) < epsilon
vITRF_per_second = vITRF / seconds_per_day
epsilon = 7e-8 # Why not 1e-9, which would match all of their digits?
assert abs(-3.225636520 - vITRF_per_second[0]) < epsilon
assert abs(-2.872451450 - vITRF_per_second[1]) < epsilon
assert abs(+5.531924446 - vITRF_per_second[2]) < epsilon
def find_closest_satellite(self, t, xyz, satlist):
a = SatrecArray([sat.model for sat in satlist])
# jd = np.array([t._utc_float()]) # skyfield 1.2x or so....
jd = np.array([t.whole + t.tai_fraction - t._leap_seconds() / DAY_S])
e, r, v = a.sgp4(jd, jd * 0.0)
r = r[:,0,:] # eliminate t axis since we only have one time
v = v[:,0,:]
r = r.T # move x,y,z to top level like Skyfield expects
v = v.T
ut1 = np.array([t.ut1])
r, v = TEME_to_ITRF(ut1, r, v)
r2=np.array(xyz)
r2.shape = 3, 1 # add extra dimension to stand in for time
# sep_a = angle_between(r, r2)
sep_d = length_of(r-r2)
i = np.argmin(sep_d)
closest_satellite = satlist[i]
# closest_angle = sep_a[i] / tau * 360.0
closest_distance = sep_d[i]
if False:
print("Position:",xyz,"at",t.utc_strftime(),":")
for idx,s in enumerate(sorted(satlist, key=lambda sat: sat.name)):
print(" %s: %8.2fkm %s"%(s.name,sep_d[idx],["","*"][i==idx]))
return closest_satellite, closest_distance
def TEME_to_GCRS(time, pos, vel):
"""Convert a position and velocity from TEME to GCRS coordinates, via ITRF
* TEME: True Equator, Mean Equinox (used in TLE format and in SGP4 theory)
* ITRF: International Terrestrial Reference Frame
* GCRS: Geocentric Celestial Reference System (returned by method satellite.at)
"""
pos, vel = TEME_to_ITRF(time.whole, pos, vel, 0.0, 0.0, time.ut1_fraction)
return ITRF_to_GCRS2(time, pos, vel)
def test_appendix_c_conversion_from_TEME_to_ITRF():
rTEME = array([5094.18016210, 6127.64465950, 6380.34453270])
vTEME = array([-4.746131487, 0.785818041, 5.531931288])
vTEME = vTEME * 24.0 * 60.0 * 60.0 # km/s to km/day
jd_ut1 = JulianDate(tt=(2004, 4, 6, 7, 51, 28.386 - 0.439961)).tt
xp = -0.140682 * arcsecond
yp = 0.333309 * arcsecond
rITRF, vITRF = TEME_to_ITRF(jd_ut1, rTEME, vTEME, xp, yp)
meter = 1e-3
assert abs(-1033.47938300 - rITRF[0]) < 0.1 * meter
assert abs(+7901.29527540 - rITRF[1]) < 0.1 * meter
assert abs(+6380.35659580 - rITRF[2]) < 0.1 * meter
vITRF_per_second = vITRF * second
assert abs(-3.225636520 - vITRF_per_second[0]) < 1e-4 * meter
assert abs(-2.872451450 - vITRF_per_second[1]) < 1e-4 * meter
assert abs(+5.531924446 - vITRF_per_second[2]) < 1e-4 * meter