Implement get_predictions()

3 files changed, 48 insertions, 11 deletions

diff --git a/iss/predictions.py b/iss/predictions.py
index 7febe62..3c05ef2 100644
--- a/iss/predictions.py
+++ b/iss/predictions.py
@@ -1,24 +1,30 @@
 from skyfield.api import Topos, load
 
+from .utils import chunks
+
 
 class Predictions(object):
     ISS = "ISS (ZARYA)"
 
-    def __init__(self, lat, lng, altitude=30.0, tz="UTC", satellite=ISS):
+    def __init__(
+        self, lat, lng, altitude=30.0, tz="UTC", satellite=ISS, start=None, days=10
+    ):
         self.lat = lat
         self.lng = lng
         self.altitude = altitude
         self.tz = tz
         self.satellite = satellite
+        self.start = start
+        self.days = days
 
     def init_stations(self):
         stations_url = "http://celestrak.com/NORAD/elements/stations.txt"
         return load.tle_file(stations_url)
 
-    def get_next_days(self, days=10):
+    def get_next_days(self):
         ts = load.timescale()
-        t0 = ts.now()
-        t1 = ts.ut1_jd(t0.ut1 + days)
+        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):
@@ -31,13 +37,17 @@ class Predictions(object):
 
     def get_predictions(self):
         satellite = self.get_satellite()
-        t0, t1 = self.get_next_days(days=10)
+        t0, t1 = self.get_next_days()
         location = self.get_location()
 
-        t, events = satellite.find_events(
+        ts, _events = satellite.find_events(
             location, t0, t1, altitude_degrees=self.altitude
         )
 
-        for ti, event in zip(t, events):
-            name = ("rise above 30°", "culminate", "set below 30°")[event]
-            print(ti.utc_strftime("%Y %b %d %H:%M:%S"), name)
+        # 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]
diff --git a/iss/tests/test_predictions.py b/iss/tests/test_predictions.py
index b809885..27fc667 100644
--- a/iss/tests/test_predictions.py
+++ b/iss/tests/test_predictions.py
@@ -4,16 +4,40 @@ from ..predictions import Predictions
 
 
 def test_get_timescales():
-    p = Predictions(lat=32.0853, lng=34.7817, tz="Asia/Jerusalem")
     days = 5
-    t0, t1 = p.get_next_days(days=days)
+    p = Predictions(lat=32.0853, lng=34.7817, days=days)
+    t0, t1 = p.get_next_days()
     delta = t1.ut1 - t0.ut1
     assert delta == days
 
 
+def test_custom_start():
+    start = 2459117.245895914
+    p = Predictions(lat=32.0853, lng=34.7817, start=start)
+    t0, _t1 = p.get_next_days()
+    assert t0.ut1 == start
+
+
 def test_get_location():
     p = Predictions(lat=32.0853, lng=34.7817)
     tlv = Topos("32.0853 N", "34.7817 E")
     topos = p.get_location()
     assert topos.latitude.degrees == tlv.latitude.degrees
     assert topos.longitude.degrees == tlv.longitude.degrees
+
+
+def test_get_predictions():
+    start = 2459117.245895914
+
+    p = Predictions(lat=32.0853, lng=34.7817, tz="Asia/Jerusalem", start=start)
+    preds = p.get_predictions()
+    assert len(preds) == 17
+    assert preds[0] == [
+        "2020-09-24T21:31:09Z",
+        "2020-09-24T21:32:35Z",
+        "2020-09-24T21:34:02Z",
+    ]
+
+    p = Predictions(lat=32.0853, lng=34.7817, tz="Asia/Jerusalem", start=start, days=5)
+    preds = p.get_predictions()
+    assert len(preds) == 8
diff --git a/iss/utils.py b/iss/utils.py
new file mode 100644
index 0000000..f1a75c0
--- /dev/null
+++ b/iss/utils.py
@@ -0,0 +1,3 @@
+def chunks(l, n):
+    for i in range(0, len(l), n):
+        yield l[i : i + n]