def test_observing_earth_from_location_on_moon_with_time_vector():
# See the above test for a more thorough blow-by-blow test of this
# complete operation. Here, we simply run through it quickly and
# test only the end result, to see if the operation more thoroughly
# tested above will also work when given a time vector.
ts = load.timescale()
t = ts.utc(2019, 12, [13, 14])
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_ME_DE421')
pt = pc.build_latlon_degrees(frame, 26.3, 313.2)
eph = load('de421.bsp')
astrometric = (eph['moon'] + pt).at(t).observe(eph['earth'])
apparent = astrometric.apparent()
alt, az, distance = apparent.altaz()
want = (42.0019, 40.7411), (114.9380, 116.3859)
pair = alt.degrees, az.degrees
arcsecond = 1.0 / 3600.0
assert abs(np.array(want) - pair).max() < 12 * arcsecond
def test_rotating_vector_into_frame():
et_seconds = 259056665.1855896
ts = load.timescale()
t = ts.tdb_jd(T0 + et_seconds / 3600. / 24.0)
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
# Example from "moon_080317.tf" (the raw vector is taken from a
# tweaked version of the script in the file that uses "J2000"):
vector = ICRF(
np.array([
2.4798273371071659e+05, -2.6189996683651494e+05,
-1.2455830876097400e+05
]) / AU_KM)
vector.t = t
meter = 1e-3
frame = pc.build_frame_named('MOON_PA_DE421')
result = vector.frame_xyz(frame)
assert max(abs(result.km - [379908.634, 33385.003, -12516.8859])) < meter
relative_frame = pc.build_frame_named('MOON_ME_DE421')
result = vector.frame_xyz(relative_frame)
assert max(abs(result.km - [379892.825, 33510.118, -12661.5278])) < meter
def test_unloaded_bpc():
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
try:
pc.build_frame_named('MOON_PA_DE421')
except LookupError as e:
assert str(e) == ('you have not yet loaded a binary PCK file'
' that has a segment for frame 31006')
def test_frame_alias():
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
f1 = pc.build_frame_named('MOON_PA_DE421')
f2 = pc.build_frame_named('MOON_PA')
ts = load.timescale()
t = ts.tdb_jd(T0)
assert (f1.rotation_at(t) == f2.rotation_at(t)).all()
def moon_subsolar_point(t):
eph = load('de421.bsp')
sun = eph['sun']
moon = eph['moon']
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_ME_DE421')
place = moon + pc.build_latlon_degrees(frame, 90.0, 180.0)
sunpos = place.at(t).observe(sun).apparent()
lat, lon, dist = sunpos.altaz()
return lat.degrees, wrap180(lon.degrees), dist.km
def run():
rospy.init_node('sun_seeker_node', anonymous=True)
rospy.Subscriber('/clock', Clock, sim_time_callback)
pub = rospy.Publisher('/sun_seeker/vector', Vector3, queue_size=1)
rate = rospy.Rate(0.1)
eph = load('de421.bsp')
sun = eph['sun']
moon = eph['moon']
path = os.path.realpath(__file__)
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_ME_DE421')
place = moon + pc.build_latlon_degrees(frame, -86.79430, -21.18640)
sun_angle_msg = Vector3()
while not rospy.is_shutdown():
dt = datetime.fromtimestamp(sim_time)
dt_utc = dt.replace(tzinfo=pytz.UTC)
ts = load.timescale()
t = ts.from_datetime(dt_utc)
sunpos = place.at(t).observe(sun).apparent()
alt, az, distance = sunpos.altaz()
sun_angle_msg.x = 0.0
sun_angle_msg.y = alt.degrees
sun_angle_msg.z = az.degrees
if rospy.get_time() - last_msg_time < msg_timeout:
rospy.loginfo('Publishing vector: x = {0:.3f}, y = {1:.3f}, z = {2:.3f}'.format(sun_angle_msg.x, sun_angle_msg.y, sun_angle_msg.z))
pub.publish(sun_angle_msg)
else:
rospy.logwarn('Timeout {0:.1f} seconds: Is /clock publishing?'.format(msg_timeout))
rate.sleep()
def test_using_elevation_to_locate_center_of_moon():
# Test the `elevation_m` parameter by using it to offset a Moon
# surface location back to the Moon's center.
ts = load.timescale()
t = ts.utc(2020, 4, 23)
eph = load('de421.bsp')
a1 = eph['moon'].at(t)
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_ME_DE421')
place = pc.build_latlon_degrees(frame, 26.3, 313.2, -1737400)
a2 = (eph['moon'] + place).at(t)
mm = 1e-3
assert max(abs(a1.position.m - a2.position.m)) < mm
def test_horizons_position_of_latitude_longitude_on_moon():
# This test against HORIZON is low-precision, with agreement only
# within about 100m. This is a symptom of the fact that here we are
# using the recent high-accuracy MOON_ME frame, while HORIZONS says
# it is using the old "IAU_MOON". Alas, the NAIF presentation
# `23_lunar-earth_pck-fk.pdf` says that the worse-case agreement
# between the frames is 155m and is on average only 76m, so our low
# agreement here is reasonable.
#
# See the file `horizons/moon-from-moon-topos` for the HORIZONS
# result this test compares against.
ts = load.timescale()
t = ts.tdb_jd(2458827.5)
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_ME_DE421')
assert frame.center == 301
pt = pc.build_latlon_degrees(frame, 26.3, -46.8)
assert pt.center == 301
geometric = pt.at(t)
assert geometric.center == 301
# Note that the sign of these two vectors is flipped, since HORIZONS
# measured the other direction, from the surface to the center.
want = -1.043588965592271E-05, -3.340834944508400E-06, 3.848560523814720E-06
meter = 1.0 / AU_M
assert abs(geometric.position.au - want).max() < 101 * meter
want = 3.480953228580460E-07, -2.173626424774260E-06, -9.429610667799021E-07
assert abs(geometric.velocity.au_per_d - want).max() < 1.6e-10
def test_observing_earth_from_location_on_moon():
ts = load.timescale()
t = ts.utc(2019, 12, 13)
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_ME_DE421')
assert frame.center == 301
pt = pc.build_latlon_degrees(frame, 26.3, 313.2)
assert pt.center == 301
eph = load('de421.bsp')
astrometric = (eph['moon'] + pt).at(t).observe(eph['earth'])
# See the file `horizons/earth-from-moon-topos` for the HORIZONS
# source of the following `want` values.
ra, dec, distance = astrometric.radec()
want = 270.2590484, -22.8079717
arcsecond = 1.0 / 3600.0
assert abs(ra._degrees - want[0]) < 0.03 * arcsecond
assert abs(dec.degrees - want[1]) < 0.03 * arcsecond
# See the file `horizons/earth-from-moon-topos` for the HORIZONS
# source of these angles. TODO: Investigate how we descended from
# the brilliant sub-arcsecond precision of the previous result to a
# mere 12 arcseconds of agreement.
apparent = astrometric.apparent()
alt, az, distance = apparent.altaz()
want = 42.0019, 114.9380
pair = alt.degrees, az.degrees
assert abs(np.array(want) - pair).max() < 12 * arcsecond
def test_frame_rotation_matrices():
# To produce the following matrices:
#
# import numpy as np
# import spiceypy as spice
# from skyfield.constants import DAY_S
# spice.furnsh('moon_080317.tf')
# spice.furnsh('moon_pa_de421_1900-2050.bpc')
# g = np.vectorize(repr)
# print(g(spice.pxform('J2000', 'MOON_PA', (tdb - T0) * DAY_S)))
# print(g(spice.sxform('J2000', 'MOON_PA', (tdb - T0) * DAY_S)[3:6,:3]))
ts = load.timescale()
pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))
frame = pc.build_frame_named('MOON_PA_DE421')
assert frame._matrix is None # pure segment, with no rotation applied
# First, a moment when the angle W is nearly zero radians, so all of
# its precision is available to the trigonometry.
tdb = T0 - 11150
desired_rotation = [
[0.9994150897380264, 0.032310270603926675, 0.011203785852719871],
[-0.034157426811763446, 0.9272642685944782, 0.37284614304233643],
[0.0016578894811167893, -0.3730107540024127, 0.9278255379116378],
]
desired_rate = [
[
-9.091699265305538e-08, 2.4682369763316187e-06,
9.920226874449144e-07
],
[
-2.660127501349402e-06, -8.620891007588608e-08,
-2.930074158824601e-08
],
[
4.245963144600506e-10, -5.067878765502927e-10,
-2.045010122720299e-10
],
]
R = frame.rotation_at(ts.tdb_jd(tdb))
assert (R == desired_rotation).all() # Boom.
R2, Rv = frame.rotation_and_rate_at(ts.tdb_jd(tdb))
assert (R == R2).all()
if IS_32_BIT:
assert abs(Rv - desired_rate).max() < 3e-26
else:
assert (Rv == desired_rate).all() # Boom.
# Second, a moment when the angle W is more than 2500 radians.
tdb = T0
desired_rotation = [
[0.7840447406961362, 0.5582359944893811, 0.2713787372716964],
[-0.6203032939745002, 0.7203957219351799, 0.31024800934393754],
[-0.02230847532023746, -0.41158544468183367, 0.9110981032001678],
]
desired_rate = [
[
-1.6512401259577911e-06, 1.9173507906460613e-06,
8.265640603882371e-07
],
[
-2.0870970217531474e-06, -1.4860137438942676e-06,
-7.223743806558455e-07
],
[
-5.817943897465853e-10, -4.4636767256698343e-10,
-2.1589045361778893e-10
],
]
R = frame.rotation_at(ts.tdb_jd(tdb))
delta = abs(R - desired_rotation)
assert (delta < 2e-13).all() # a few digits are lost in large W radians?
R2, Rv = frame.rotation_and_rate_at(ts.tdb_jd(tdb))
assert (R == R2).all()
assert abs(Rv - desired_rate).max() < 4e-19 # About 13 digits precision.
# Finally, a frame which is defined by a constant rotation of
# another frame.
tdb = T0 - 11150
desired_rotation = [
[0.9994268420493244, 0.03186286343877705, 0.011434392191818011],
[-0.03382833397374688, 0.9272754001640859, 0.37284846261060917],
[0.0012771890522186643, -0.37302156798771835, 0.927821792481783],
]
desired_rate = [
[
-9.004087820606406e-08, 2.4682648578114788e-06,
9.920321321295625e-07
],
[
-2.660157295439155e-06, -8.539614878340816e-08,
-2.8974080519384074e-08
],
[
4.550211407392054e-10, -1.4469992803332584e-09,
-5.823780954758093e-10
],
]
frame = pc.build_frame_named('MOON_ME_DE421')
R = frame.rotation_at(ts.tdb_jd(tdb))
delta = abs(R - desired_rotation)
if IS_32_BIT:
assert abs(R - desired_rotation).max() < 2e-16
else:
assert (R == desired_rotation).all()
R2, Rv = frame.rotation_and_rate_at(ts.tdb_jd(tdb))
assert (R == R2).all()
if IS_32_BIT:
assert abs(Rv - desired_rate).max() < 2e-23
else:
assert (Rv == desired_rate).all()