def test_gei_gei():
# Test GEI loopback transformation using the 2017 revision to Franz & Harper 2002
t = Time('1996-08-28 16:46:00', scale='tt')
gei_j2000 = CartesianRepresentation([-5.7840451, -4.1082375, 1.9146822] * (6378.14*u.km))
gei_d = CartesianRepresentation([-5.7864918, -4.1039136, 1.9165612] * (6378.14*u.km))
old = SkyCoord(gei_j2000, frame=GeocentricEarthEquatorial(obstime=t))
new = old.transform_to(GeocentricEarthEquatorial(equinox=t, obstime=t)).cartesian
assert_quantity_allclose(new.xyz, gei_d.xyz)
def test_hme_gei_sunspice():
# Compare our HME->GEI transformation against SunSPICE
# "HAE" is equivalent to Astropy's Heliocentric Mean Ecliptic, and defaults to J2000.0
#
# IDL> coord = [1.d, 120.d, 10.d]
# IDL> convert_sunspice_lonlat, '2019-06-01', coord, 'HAE', 'GEI', /au, /degrees
# IDL> print, coord
# 1.8197210 95.230617 28.830109
old = SkyCoord(120*u.deg, 10*u.deg, 1*u.AU,
frame=HeliocentricMeanEcliptic(obstime='2019-06-01'))
new = old.transform_to(GeocentricEarthEquatorial)
assert_quantity_allclose(new.lon, Longitude(95.230617*u.deg), atol=0.01*u.arcsec, rtol=0)
assert_quantity_allclose(new.lat, 28.830109*u.deg, atol=0.05*u.arcsec, rtol=0)
assert_quantity_allclose(new.distance, 1.8197210*u.AU)
# Transform from HAE precessed to the mean ecliptic of date instead of J2000.0
# IDL> coord = [1.d, 120.d, 10.d]
# IDL> convert_sunspice_lonlat, '2019-06-01', coord, 'HAE', 'GEI', /au, /degrees, /precess
# IDL> print, coord
# 1.8217103 95.079030 28.827750
old = SkyCoord(120*u.deg, 10*u.deg, 1*u.AU,
frame=HeliocentricMeanEcliptic(obstime='2019-06-01', equinox='2019-06-01'))
new = old.transform_to(GeocentricEarthEquatorial(equinox=_J2000))
assert_quantity_allclose(new.lon, Longitude(95.079030*u.deg), atol=0.05*u.arcsec, rtol=0)
assert_quantity_allclose(new.lat, 28.827750*u.deg, atol=0.05*u.arcsec, rtol=0)
assert_quantity_allclose(new.distance, 1.8217103*u.AU)