Use pyongc dataframes with starlib from_dataframe()

Signed-off-by: Mattia Verga <[email protected]>

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[data]
 python-dateutil>=2.5.0
 pytz
 sphinx==1.7.2

skyfield/data/ongc.py

@@ -0,0 +1,29 @@
+from math import pi
+
+PANDAS_MESSAGE = """Skyfield needs Pandas to load the OpenNGC catalog
+
+To load the OpenNGC star catalog, Skyfield needs the Pandas data
+analysis toolkit.  Try installing it using your usual Python package
+installer, like "pip install pandas" or "conda install pandas".
+"""
+
+def load_dataframe(in_dataframe):
+    """Convert a dataframe from pyongc.data for import in skyfield."""
+    try:
+        from pandas import read_csv
+    except ImportError:
+        raise ImportError(PANDAS_MESSAGE)
+
+    df = in_dataframe[['name', 'ra', 'dec', 'parallax', 'pmra', 'pmdec']].copy()
+
+    df = df.assign(
+        ra_hours = df['ra'] * 180 / pi / 15.0,
+        dec_degrees = df['dec'] * 180 / pi,
+        epoch_year = 2000,
+    )
+
+    df.rename(columns = {'parallax':'parallax_mas',
+                         'pmra':'ra_mas_per_year',
+                         'pmdec':'dec_mas_per_year'}, inplace = True)
+
+    return df.set_index('name')

skyfield/tests/test_stars.py

@@ -1,8 +1,18 @@
+from pyongc import data
 from skyfield import api
-from skyfield.data.hipparcos import load_dataframe
+from skyfield.data import hipparcos, ongc
 
 def test_dataframe():
     with api.load.open('hip_main.dat.gz') as f:
-        df = load_dataframe(f)
+        df = hipparcos.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_dataframe_from_ongc():
+    ongc_data = data.all()
+    df = ongc.load_dataframe(ongc_data)
+    hercules = api.Star.from_dataframe(df.loc['NGC6205'])
+    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)'
+    )