def itrs_pos_sun(self):
"""Determine unit vector pointing from given position to Sun in ITRS
The determination of the vector pointing from given position to Sun is based on Eq. 5.77 in
:cite:`subirana2013`.
Returns:
numpy.ndarray: unit vectors pointing from given position to Sun in ITRS and in unit of meters
"""
# Get Sun position vector in ITRS
eph = apriori.get(
"ephemerides",
time=self._time.tdb) # TODO: is self._time.tdb correct
# TODO:
# Actually the JPL ephemeris are given in the BCRS with Solar System barycenter as origin and not Earth mass
# center. So in principle the sun position vector has to be transformed from the BCRS to the GCRS. What are
# the consequences, if we do not consider these corrections?
earth_sun = eph.itrs(
"earth", "sun") # vector pointing from Earth to Sun mass center
# Determination of vector between given position and Sun
pos_sun = earth_sun - self.itrs_pos
pos_sun_unit = mathp.unit_vector(pos_sun)
# +DEBUG: Use same model as gLAB for determination of sun-earth vector
# glab_sun_earth = gnss.findsun(self._time.tdb)
# glab_pos_sun = glab_sun_earth - self.itrs_pos
# pos_sun_unit = mathp.unit_vector(glab_pos_sun)
# -DEBUG
return pos_sun_unit
def _itrs2yaw(self):
"""Transformation matrix from ITRS to yaw-steering reference system
The yaw-steering reference system given with x-axis lying in the Earth-Satellite-Sun plane, y-axis as the
normal vector of the Earth-Satellite-Sun plane and the z-axis pointing to the Earth's center.
Returns:
numpy.ndarray: transformation matrix with shape (num_obs, 3, 3).
"""
z_unit = -mathp.unit_vector(self.itrs_pos) # unit vector of z-axis
sat_sun_unit = self.itrs_pos_sun # unit vector pointing from satellite position to Sun
y_unit = mathp.unit_vector(np.cross(
z_unit, sat_sun_unit)) # unit vector of y-axis
x_unit = mathp.unit_vector(np.cross(y_unit,
z_unit)) # unit vector of x-axis
itrs2yaw = np.stack((x_unit, y_unit, z_unit), axis=1)
return itrs2yaw
def _itrs2acr(self):
"""Transformation matrix from ITRS to local orbital reference system given with along-track, cross-track and
radial.
Returns:
numpy.ndarray: transformation matrix with shape (num_obs, 3, 3).
"""
r_unit = mathp.unit_vector(
self.itrs_pos
) # unit vector of satellite position and in radial direction
v_unit = mathp.unit_vector(
self.itrs_vel) # unit vector of satellite velocity
c_unit = mathp.unit_vector(np.cross(
r_unit, v_unit)) # unit vector cross-track direction
a_unit = mathp.unit_vector(np.cross(
c_unit, r_unit)) # unit vector along-track direction
itrs2acr = np.stack((a_unit, c_unit, r_unit), axis=1)
return itrs2acr
def check_satellite_eclipse(dset):
"""Check if a satellite is an eclipse
TODO: Check if a better algorithm exists (e.g. based on beta angle).
Args:
dset(Dataset): Model data
"""
cos_gamma = np.einsum(
"ij,ij->i", mathp.unit_vector(dset.sat_posvel.itrs_pos),
dset.sat_posvel.itrs_pos_sun
) # TODO: dot product -> better solution dot() function in mathp
h = np.linalg.norm(dset.sat_posvel.itrs_pos,
axis=1) * np.sqrt(1.0 - cos_gamma**2)
satellites_in_eclipse = list()
for satellite in dset.unique("satellite"):
idx = dset.filter(satellite=satellite)
satellite_eclipse = np.logical_and(cos_gamma[idx] < 0,
h[idx] < constant.a)
if np.any(satellite_eclipse == True):
satellites_in_eclipse.append(satellite)
return satellites_in_eclipse
def get_line_of_sight(dset):
"""Get the Line of Sight vector from receiver to satellite in the ITRS.
"""
# TODO: Other solution dset.site_pos.convert_gcrs_to_itrs(dset.site_pos.direction)
return mathp.unit_vector(dset.sat_posvel.itrs_pos - dset.site_pos.itrs)
