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Make get_observer_look work on oblate earth #87

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Make get_observer_look work on oblate earth #87

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894d731
Factorize `get_observer_look` method and function
mraspaud Nov 12, 2021
6785eed
Fixing style errors.
stickler-ci Nov 12, 2021
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54 changes: 10 additions & 44 deletions pyorbital/orbital.py
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Original file line number Diff line number Diff line change
Expand Up @@ -103,42 +103,39 @@ def get_observer_look(sat_lon, sat_lat, sat_alt, utc_time, lon, lat, alt):
(pos_x, pos_y, pos_z), (vel_x, vel_y, vel_z) = astronomy.observer_position(
utc_time, sat_lon, sat_lat, sat_alt)

az_, el_ = get_observer_look_from_cartesian_position(utc_time, lon, lat, alt, pos_x, pos_y, pos_z)

return az_, el_


def get_observer_look_from_cartesian_position(utc_time, lon, lat, alt, pos_x, pos_y, pos_z):
(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

# Azimuth is undefined when elevation is 90 degrees, 180 (pi) will be returned.
az_ = np.arctan2(-top_e, top_s) + np.pi
az_ = np.mod(az_, 2 * np.pi) # Needed on some platforms

rg_ = np.sqrt(rx * rx + ry * ry + rz * rz)

top_z_divided_by_rg_ = top_z / rg_

# Due to rounding top_z can be larger than rg_ (when el_ ~ 90).
top_z_divided_by_rg_ = top_z_divided_by_rg_.clip(max=1)
el_ = np.arcsin(top_z_divided_by_rg_)

return np.rad2deg(az_), np.rad2deg(el_)
az_, el_ = np.rad2deg(az_), np.rad2deg(el_)
return az_, el_


class Orbital(object):
Expand Down Expand Up @@ -254,40 +251,9 @@ def get_observer_look(self, utc_time, lon, lat, alt):
"""

utc_time = dt2np(utc_time)
(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_)
(pos_x, pos_y, pos_z), (vel_x, vel_y, vel_z) = self.get_position(utc_time, normalize=False)

return np.rad2deg(az_), np.rad2deg(el_)
return get_observer_look_from_cartesian_position(utc_time, lon, lat, alt, pos_x, pos_y, pos_z)

def get_orbit_number(self, utc_time, tbus_style=False, as_float=False):
"""Calculate orbit number at specified time.
Expand Down