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from skyfield.api import Topos, load
from .utils import chunks
ISS = "ISS (ZARYA)"
STATIONS_URL = "http://celestrak.com/NORAD/elements/stations.txt"
class Predictions(object):
def __init__(
self,
lat,
lng,
altitude=30.0,
tz="UTC",
satellite=ISS,
start=None,
days=10,
tle_file=None,
):
self.lat = lat
self.lng = lng
self.altitude = altitude
self.tz = tz
self.satellite = satellite
self.start = start
self.days = days
self.tle_file = tle_file.resolve().as_posix() if tle_file else STATIONS_URL
def init_stations(self):
return load.tle_file(self.tle_file)
def get_next_days(self):
ts = load.timescale()
t0 = ts.now() if not self.start else ts.ut1_jd(self.start)
t1 = ts.ut1_jd(t0.ut1 + self.days)
return t0, t1
def get_location(self):
return Topos(latitude_degrees=self.lat, longitude_degrees=self.lng)
def get_satellite(self):
satellites = self.init_stations()
by_name = {sat.name: sat for sat in satellites}
return by_name[self.satellite]
def get_prediction_events(self):
satellite = self.get_satellite()
t0, t1 = self.get_next_days()
location = self.get_location()
ts, _events = satellite.find_events(
location, t0, t1, altitude_degrees=self.altitude
)
# events are returned as 3-tuples of (rise, culminate, set)
# where rise/set are relative to given altitude
# docs mention the possibilibity of several culminations
# https://rhodesmill.org/skyfield/earth-satellites.html#finding-when-a-satellite-rises-and-sets
# but this doesn't seem to happen in our case
preds = chunks(ts, 3)
return [[t.utc_iso() for t in p] for p in preds]
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