I am trying to draw polygons on a map at arbitrary locations, including places that span the pole and the dateline. Conceptually, consider drawing instrument footprints for orbital measurements, where the corners of the footprints are known in lat/long (or cartesian). I have been able to get mid-latitude polygons to draw, but shapes spanning the pole come up blank.

Here is some code to show where I have gotten:

from matplotlib.patches import Polygon
import matplotlib.pyplot as plt
import cartopy.crs as ccrs

# /questions/73689586/
geodetic = ccrs.Geodetic()

# Define a polygon over the pole (long, lat)
points_north = [ (0,   75),
                 (270, 75),
                 (180, 75),
                 (90,  75), ]

# Mid-latitude polygon (long, lat)
points_mid = [ (10,  70),
               (30,  20),
               (60,  20),
               (80,  70), ]

# Create a PlateCarree projection
proj0 = ccrs.PlateCarree()
proj0._threshold /= 5.                 # /questions/59020032/
ax = plt.axes( projection = proj0 )

# Add the polygons to the plot
ax.add_patch( Polygon( points_north, alpha = 0.2, transform = geodetic ) )
ax.add_patch( Polygon( points_mid,   alpha = 0.2, transform = geodetic ) )

# Some window dressing
longlocs = list( range( -180, 181, 30 ) )
latlocs = [ -75, -60, -30, 0, 30, 60, 75 ]
ax.gridlines( xlocs = longlocs, ylocs = latlocs,
              draw_labels = True,  crs = proj0 )
ax.set_global()
ax.set_xlabel('Longitude')
ax.set_ylabel('Latitude')

# Show the plot
plt.show()

This produces the following map:

Polygon projections

The mid-latitude polygon draws as expected, but the north pole square does not. I would expect that polygon to be smeared across the entire north with scalloped edges, similar to what is shown in the rotated pole boxes example.

I have played around with RotatedPole but I really haven’t come close to a general solution that lets me plot arbitrary footprints.