def _find_next_pass(self, start_date):
def elevation(delta_seconds):
return self._elevation_at(start_date +
dt.timedelta(seconds=delta_seconds))
start_elevation = self._elevation_at(start_date)
period_s = orbital_period(self.predictor.mean_motion) * 60
# Find date for maximum elevation within the next orbital period
# NOTE: This is the most expensive operation
res_tca = minimize_scalar(
lambda t: -elevation(t),
bounds=(0, period_s),
method=minimize_scalar_bounded_alt,
options=dict(xatol=self.tolerance_s),
)
t_tca = res_tca.x
tca = start_date + dt.timedelta(seconds=t_tca)
max_elevation = -res_tca.fun
if max_elevation < self.max_elevation_gt:
return False, None, tca, start_date + dt.timedelta(
seconds=period_s), max_elevation
# Find AOS
try:
if self.aos_at < start_elevation:
# AOS is past the start date
t_left = -period_s / 2
else:
t_left = 0
t_aos = root_scalar(
lambda t: elevation(t) - self.aos_at,
bracket=(t_left, t_tca),
xtol=self.tolerance_s,
).root
except ValueError as e:
raise PropagationError(
"Could not find AOS of pass with TCA {}".format(tca)) from e
# Ensure location is visible at AOS by adding atol
aos = start_date + dt.timedelta(seconds=t_aos + self.tolerance_s)
# LOS must be between TCA and half the next period
try:
t_los = root_scalar(
lambda t: elevation(t) - self.aos_at,
bracket=(t_tca, t_tca + period_s / 2),
xtol=self.tolerance_s,
).root
except ValueError as e:
raise PropagationError(
"Could not find LOS of pass with AOS {} and TCA {}".format(
aos, tca)) from e
else:
los = start_date + dt.timedelta(seconds=t_los)
return True, aos, tca, los, max_elevation
def _find_nearest_ascending(self, descending_date):
for candidate in self._sample_points(descending_date):
if self.is_ascending(candidate):
return candidate
else:
logger.error('Could not find an ascending pass over %s start date: %s - TLE: %s',
self.location, descending_date, self.propagator.tle)
raise PropagationError('Can not find an ascending phase')