def get_lonlatalt(self, utc_time):
"""Calculate sublon, sublat and altitude of satellite.
http://celestrak.com/columns/v02n03/
"""
(pos_x, pos_y, pos_z), (vel_x, vel_y, vel_z) = self.get_position(
utc_time, normalize=True)
lon = ((np.arctan2(pos_y * XKMPER, pos_x * XKMPER) - astronomy.gmst(utc_time))
% (2 * np.pi))
lon = np.where(lon > np.pi, lon - np.pi * 2, lon)
lon = np.where(lon <= -np.pi, lon + np.pi * 2, lon)
r = np.sqrt(pos_x ** 2 + pos_y ** 2)
lat = np.arctan2(pos_z, r)
e2 = F * (2 - F)
while True:
lat2 = lat
c = 1 / (np.sqrt(1 - e2 * (np.sin(lat2) ** 2)))
lat = np.arctan2(pos_z + c * e2 * np.sin(lat2), r)
if np.all(abs(lat - lat2) < 1e-10):
break
alt = r / np.cos(lat) - c
alt *= A
return np.rad2deg(lon), np.rad2deg(lat), alt
def __init__(self, tle):
self.epoch = tle.epoch
self.excentricity = tle.excentricity
self.inclination = np.deg2rad(tle.inclination)
self.right_ascension = np.deg2rad(tle.right_ascension)
self.arg_perigee = np.deg2rad(tle.arg_perigee)
self.mean_anomaly = np.deg2rad(tle.mean_anomaly)
self.mean_motion = tle.mean_motion * (np.pi * 2 / XMNPDA)
self.mean_motion_derivative = tle.mean_motion_derivative * \
np.pi * 2 / XMNPDA ** 2
self.mean_motion_sec_derivative = tle.mean_motion_sec_derivative * \
np.pi * 2 / XMNPDA ** 3
self.bstar = tle.bstar * AE
n_0 = self.mean_motion
k_e = XKE
k_2 = CK2
i_0 = self.inclination
e_0 = self.excentricity
a_1 = (k_e / n_0) ** (2.0 / 3)
delta_1 = ((3 / 2.0) * (k_2 / a_1**2) * ((3 * np.cos(i_0)**2 - 1) /
(1 - e_0**2)**(2.0 / 3)))
a_0 = a_1 * (1 - delta_1 / 3 - delta_1**2 - (134.0 / 81) * delta_1**3)
delta_0 = ((3 / 2.0) * (k_2 / a_0**2) * ((3 * np.cos(i_0)**2 - 1) /
(1 - e_0**2)**(2.0 / 3)))
# original mean motion
n_0pp = n_0 / (1 + delta_0)
self.original_mean_motion = n_0pp
# semi major axis
a_0pp = a_0 / (1 - delta_0)
self.semi_major_axis = a_0pp
self.period = np.pi * 2 / n_0pp
self.perigee = (a_0pp * (1 - e_0) / AE - AE) * XKMPER
self.right_ascension_lon = (self.right_ascension
- astronomy.gmst(self.epoch))
if self.right_ascension_lon > np.pi:
self.right_ascension_lon -= 2 * np.pi
def get_observer_look(self, utc_time, lon, lat, alt):
"""Calculate observers look angle to a satellite.
http://celestrak.com/columns/v02n02/
utc_time: Observation time (datetime object)
lon: Longitude of observer position on ground
lat: Latitude of observer position on ground
alt: Altitude above sea-level (geoid) of observer position on ground
Return: (Azimuth, Elevation)
"""
(pos_x, pos_y, pos_z), (vel_x, vel_y, vel_z) = self.get_position(
utc_time, normalize=False)
(opos_x, opos_y, opos_z), (ovel_x, ovel_y, ovel_z) = \
astronomy.observer_position(utc_time, lon, lat, alt)
lon = np.deg2rad(lon)
lat = np.deg2rad(lat)
theta = (astronomy.gmst(utc_time) + lon) % (2 * np.pi)
rx = pos_x - opos_x
ry = pos_y - opos_y
rz = pos_z - opos_z
sin_lat = np.sin(lat)
cos_lat = np.cos(lat)
sin_theta = np.sin(theta)
cos_theta = np.cos(theta)
top_s = sin_lat * cos_theta * rx + \
sin_lat * sin_theta * ry - cos_lat * rz
top_e = -sin_theta * rx + cos_theta * ry
top_z = cos_lat * cos_theta * rx + \
cos_lat * sin_theta * ry + sin_lat * rz
az_ = np.arctan(-top_e / top_s)
az_ = np.where(top_s > 0, az_ + np.pi, az_)
az_ = np.where(az_ < 0, az_ + 2 * np.pi, az_)
rg_ = np.sqrt(rx * rx + ry * ry + rz * rz)
el_ = np.arcsin(top_z / rg_)
return np.rad2deg(az_), np.rad2deg(el_)
