satellites.py

# Symphony of the Satellites
# https://hackpad.com/Symphony-of-the-Satellites-c0aGX4vfmTN

import math
import requests
import requests_cache
import ephem
import datetime
from math import degrees
import json
from calendar import timegm

requests_cache.install_cache('satellite', backend='memory', expire_after=300)

def chunks(l, n):
    """ Yield successive n-sized chunks from l"""
    for i in xrange(0, len(l), n):
        yield l[i:i+n]

def get_satellites(only_visible = True, now=None, lat=None, lng=None):
    SAT_BRIGHTEST = 'http://celestrak.com/NORAD/elements/visual.txt'
    SAT_GEO = 'http://celestrak.com/NORAD/elements/geo.txt'
    SAT_DEBRIS = 'http://celestrak.com/NORAD/elements/1999-025.txt'
    # Fetch the ~100 brightest satellites
    r = requests.get(SAT_BRIGHTEST)
    data = r.text.split('\r\n')
    # Split each into TLE
    if only_visible:
        for tle in chunks(data, 3):
            if len(tle) != 3:
                continue
            tle_data = get_location(tle, now=now, lat=lat, lng=lng)
            if tle_data['visible']:
                yield tle_data
    else:
        for tle in chunks(data, 3):
            if len(tle) != 3:
                continue
            yield get_location(tle, now = now)

def get_location(tle, now=None, lat=None, lng=None):
    """Compute the current location of the ISS"""
    now = now or datetime.datetime.utcnow()
    lat = lat or 37.7701
    lng = lng or -122.4664

    satellite = ephem.readtle(str(tle[0]), str(tle[1]), str(tle[2]))

    # Compute for current location
    observer = ephem.Observer()
    observer.lat = lat
    observer.lon = lng
    observer.elevation = 0
    observer.date = now
    satellite.compute(observer)
    lon = degrees(satellite.sublong)
    lat = degrees(satellite.sublat)

    # Return the relevant timestamp and data
    data = {'position': {'latitude': lat,
                         'longitude': lon},
            'visible': float(repr(satellite.alt)) > 0 and float(repr(satellite.alt)) < math.pi,
            'altitude': satellite.alt,
            'azimuth': satellite.az,
            'range': satellite.range,
            'velocity': satellite.range_velocity,
            'name': satellite.name}
    return data