Add from_ongc() to starlib

Signed-off-by: Mattia Verga <mattia.verga@tiscali.it>

Author: mattiaverga

requirements.txt

@@ -7,6 +7,7 @@ numpy==1.15.4
 matplotlib==3.3.0
 pandas==1.0.0
 pyflakes==2.1.1
+pyongc
 python-dateutil>=2.5.0
 pytz
 sphinx==1.7.2

setup.py

@@ -60,4 +60,7 @@ def make_distribution(self):
         'numpy',
         'sgp4>=2.2',
         ],
+    extras_require={
+        'ongc': ['pyongc'],
+    },
 )

skyfield/starlib.py

@@ -106,6 +106,18 @@ def from_dataframe(cls, df):
             epoch=epoch,
         )
 
+    @classmethod
+    def from_ongc(cls, identifier):
+        from pyongc import ongc
+        deepsky = ongc.Dso(identifier)
+        return cls(
+            ra = Angle(radians=deepsky.rad_coords[0]),
+            dec = Angle(radians=deepsky.rad_coords[1]),
+            ra_mas_per_year = deepsky.pm_ra or 0,
+            dec_mas_per_year = deepsky.pm_dec or 0,
+            parallax_mas = deepsky.parallax or 0,
+        )
+
     def _observe_from_bcrs(self, observer):
         position, velocity = self._position_au, self._velocity_au_per_d
         t = observer.t

skyfield/tests/test_stars.py

@@ -6,3 +6,10 @@ def test_dataframe():
         df = load_dataframe(f)
     star = api.Star.from_dataframe(df)
     assert repr(star) == 'Star(ra shape=9933, dec shape=9933, ra_mas_per_year shape=9933, dec_mas_per_year shape=9933, parallax_mas shape=9933, epoch shape=9933)'
+
+def test_from_ongc():
+    hercules = api.Star.from_ongc('M13')
+    assert repr(hercules) == (
+        'Star(ra=250.42345833333337, dec=36.46130555555556, ra_mas_per_year=-3.18, '
+        'dec_mas_per_year=-2.56, parallax_mas=0.0813, epoch=2451545.0)'
+    )