Update test repr to match new ci/hip_main.dat.gz

requirements.txt

@@ -3,13 +3,12 @@ beautifulsoup4==4.6.0
 html5lib==1.0.1
 lxml==4.4.1
 mock==2.0.0
-numpy==1.14.2
-matplotlib==2.2.2
+numpy==1.15.4
+matplotlib==3.3.0
 pandas==0.23.3
 pyflakes==2.1.1
 python-dateutil>=2.5.0
 pytz
 sphinx==1.7.2
 https://github.com/brandon-rhodes/assay/archive/master.zip
-https://github.com/whiskie14142/spktype21/archive/master.zip
 -e .

skyfield/documentation/example-plots.rst

@@ -9,12 +9,170 @@ for producing images from Skyfield computations.
 For the moment there’s only example so far,
 for plotting the elevation of a satellite over time:
 
+Finder chart for comet NEOWISE
+==============================
+
 .. testsetup::
 
     import matplotlib
     matplotlib.use('Agg')  # to avoid “no display name” error on Travis CI
     del matplotlib
 
+.. testcode::
+
+    import numpy as np
+    import pandas as pd
+    from matplotlib import pyplot as plt
+
+    from skyfield import api
+    from skyfield.api import load
+    ts = load.timescale(builtin=True)
+    eph = load('de421.bsp')
+    sun = eph['sun']
+    earth = eph['earth']
+
+
+    # In[3]:
+
+
+    t_comet = ts.utc(2020, 7, range(17, 27))
+    t = t_comet[len(t_comet) // 2]  # middle date
+
+
+    # In[4]:
+
+
+    from skyfield.data import mpc
+
+    with load.open(mpc.COMET_URL) as f:
+        comets = mpc.load_comets_dataframe(f)
+
+    comets = comets.set_index('designation', drop=False)
+    row = comets.loc['C/2020 F3 (NEOWISE)']
+
+
+    # In[5]:
+
+
+    from skyfield.constants import GM_SUN_Pitjeva_2005_km3_s2 as GM_SUN
+
+    comet = sun + mpc.comet_orbit(row, ts, GM_SUN)
+    center = earth.at(t).observe(comet)
+
+
+    # In[6]:
+
+
+    from skyfield.api import Star
+    from skyfield.data import hipparcos
+
+
+    # In[53]:
+
+
+    from skyfield.projections import build_stereographic_projection
+    proj = build_stereographic_projection(center)
+
+
+    # In[54]:
+
+
+    with load.open(hipparcos.URL) as f:
+        stars = hipparcos.load_dataframe(f)
+
+
+    # In[55]:
+
+
+    star_positions = earth.at(t).observe(Star.from_dataframe(stars))
+    stars['x'], stars['y'] = proj(star_positions)
+
+
+    # In[56]:
+
+
+    limiting_magnitude = 6.5
+    bright_stars = (stars.magnitude <= limiting_magnitude)
+
+
+    # In[57]:
+
+
+    comet_x, comet_y = proj(earth.at(t_comet).observe(comet))
+
+
+    # In[98]:
+
+
+    # = 'https://raw.githubusercontent.com/Stellarium/stellarium/master/skycultures/western_SnT/constellationship.fab'
+    from skyfield.data.stellarium import parse_constellations
+
+    url = 'https://raw.githubusercontent.com/Stellarium/stellarium/master/skycultures/western_SnT/constellationship.fab'
+    with load.open(url) as f:
+        constellations = parse_constellations(f)
+
+    edges_star1 = [star1 for name, edges in constellations for star1, star2 in edges]
+    edges_star2 = [star2 for name, edges in constellations for star1, star2 in edges]
+
+    np.array([stars['x'].loc[edges_star1], stars['y'].loc[edges_star1]])
+    xy1 = stars[['x', 'y']].loc[edges_star1].values
+    xy2 = stars[['x', 'y']].loc[edges_star2].values
+    lines_xy = np.rollaxis(np.array([xy1, xy2]), 1)
+
+
+    # In[94]:
+
+
+    fig, ax = plt.subplots(figsize=[9, 9])
+
+    from matplotlib.collections import LineCollection
+    from skyfield.api import tau
+
+    field_of_view_degrees = 45.0
+
+    line_collection = LineCollection(lines_xy) #, color=['#0002'] * len(lines_xy))
+    ax.add_collection(line_collection)
+
+    marker_size = (0.5 + limiting_magnitude - stars.magnitude[bright_stars]) ** 2.0
+    ax.scatter(stars['x'][bright_stars], stars['y'][bright_stars], s=marker_size, color='k')
+    #ax.scatter(comet_x, comet_y, s=100, color='b')
+    #comet_color = '#f00'
+    #ax.plot(comet_x, comet_y, '+', c=comet_color, zorder=3)
+    ax.plot(comet_x, comet_y, '+', zorder=3)
+    offset = 0.002
+    for xi, yi, tstr in zip(comet_x, comet_y, t_comet.utc_strftime('%-m/%d')):
+        #text = ax.text(xi + offset, yi - offset, tstr, color=comet_color, ha='left', va='top', fontsize=12,
+        text = ax.text(xi + offset, yi - offset, tstr, ha='left', va='top', fontsize=12,
+               weight='bold')
+        text.set_alpha(0.3)
+
+    ax.set_title('Comet NEOWISE {} through {}'.format(
+        t_comet[0].utc_strftime('%Y %B %d'),
+        t_comet[-1].utc_strftime('%Y %B %d'),
+    ))
+    ax.set_aspect(1.0)
+    ax.xaxis.set_visible(False)
+    ax.yaxis.set_visible(False)
+
+    angle = (180.0 - field_of_view_degrees) / 720.0 * tau
+    limit = np.sin(angle) / (1.0 - np.cos(angle))
+    ax.set_xlim(-limit, limit)
+    ax.set_ylim(-limit, limit)
+
+    fig.savefig('neowise-finder-chart.png')
+
+
+
+.. image:: _static/neowise-finder-chart.png
+
+.. testcleanup::
+
+    import os
+    os.rename('neowise-finder-chart.png', '_static/neowise-finder-chart.png')
+
+Satellite altitude during re-entry
+==================================
+
 .. testcode::
 
     from matplotlib import pyplot as plt

skyfield/projections.py

@@ -43,8 +43,11 @@ def build_stereographic_projection(center):
     # https://math.stackexchange.com/questions/409217/
     p = center.position.au
     u = p / length_of(p)
-    c = u.mean(axis=1)
-    c = c / length_of(c)
+    if len(u.shape) > 1:
+        c = u.mean(axis=1)
+        c = c / length_of(c)
+    else:
+        c = u
     x_c, y_c, z_c = c
 
     def project(position):

skyfield/tests/test_stars.py

@@ -5,4 +5,4 @@ def test_dataframe():
     with api.load.open('hip_main.dat.gz') as f:
         df = load_dataframe(f)
     star = api.Star.from_dataframe(df)
-    assert repr(star) == 'Star(ra shape=214, dec shape=214, ra_mas_per_year shape=214, dec_mas_per_year shape=214, parallax_mas shape=214, epoch shape=214)'
+    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)'