title: Cartopy plotting points incorrectly with Orthographic projection
body: <p>I am trying to plot map points using Cartopy with Anaconda Python but am getting some strange failures with the transform. In my simple example, I am trying to plot 3 points but they are getting doubled.</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import cartopy.crs as ccrs
  
  lons = [214.5, 2.7, 197.5]                                                                                               
  lats = [35, 36, 37.]
  
  ax = plt.axes(projection=ccrs.Orthographic(
      central_longitude=0,
  central_latitude=90))
  # plot lat/lon points                                                                                                         
  ax.plot(lons, lats, 'ro',
          transform=ccrs.Geodetic())
  # plot north pole for reference                                                                                               
  ax.plot([0], [90], 'b^',
      transform=ccrs.Geodetic())
  # add coastlines for reference                                                                                                
  ax.coastlines(resolution='50m')
  ax.set_global()
  
  plt.show()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/Whuct.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Whuct.png" alt="Plot output"></a></p>
  
  <p>Tested with: </p>
  
  <p><code>cartopy==0.16.0</code> and <code>Cartopy-0.16.1.dev179-</code></p>
  
  <p><code>proj4==4.9.3</code>, <code>proj4==5.0.1</code>, <code>proj4==5.0.2</code></p>
  
  <p>My only hint was that with <code>Cartopy-0.16.1.dev179-</code> and <code>proj4==5.0.1</code>, I got this <code>UserWarning</code>:</p>
  
  <pre><code>/Users/***/anaconda3/lib/python3.6/site-packages/cartopy/crs.py:1476: UserWarning: The Orthographic projection in Proj between 5.0.0 and 5.1.0 incorrectly transforms points. Use this projection with caution.
  </code></pre>
  
  <p>I opened an issue on <a href="https://github.com/SciTools/cartopy/issues/1172" rel="nofollow noreferrer">https://github.com/SciTools/cartopy/issues/1172</a> but the issue was closed.  Anyone know how to get cartopy working correctly with Orthographic projections?</p>