BUG: Fix incorrect internal use of PlateCarree (Fixes #2377)

This replaces a couple of internal uses of PlateCarree() for lon/lat
coords with more proper geodetic CRS's on the same ellipse, which avoids
some precision problems. In the case of LambertConformal, this was
resulting in a traceback when creating a boundary on a spherical Earth
datum.

lib/cartopy/crs.py

@@ -1790,7 +1790,7 @@ def __init__(self, central_longitude=-96.0, central_latitude=39.0,
             lons[1:-1] = np.linspace(central_longitude - 180 + 0.001,
                                      central_longitude + 180 - 0.001, n)
 
-        points = self.transform_points(PlateCarree(globe=globe), lons, lats)
+        points = self.transform_points(self.as_geodetic(), lons, lats)
 
         self._boundary = sgeom.LinearRing(points)
         mins = np.min(points, axis=0)
@@ -1866,7 +1866,7 @@ def __init__(self, central_longitude=0.0, central_latitude=0.0,
         lon = central_longitude + 180
         sign = np.sign(central_latitude) or 1
         lat = -central_latitude + sign * 0.01
-        x, max_y = self.transform_point(lon, lat, PlateCarree(globe=globe))
+        x, max_y = self.transform_point(lon, lat, self.as_geodetic())
 
         coords = _ellipse_boundary(a * 1.9999, max_y - false_northing,
                                    false_easting, false_northing, 61)

lib/cartopy/tests/crs/test_lambert_conformal.py

@@ -38,6 +38,17 @@ def test_default_with_cutoff():
                               (-49788019.81831982, 30793476.08487709))
 
 
+def test_sphere():
+    """Test LambertConformal with spherical globe. (#2377)"""
+    globe = ccrs.Globe(ellipse='sphere')
+
+    # This would error creating a boundary
+    crs = ccrs.LambertConformal(globe=globe)
+
+    assert all(np.isfinite(x) for x in crs.x_limits)
+    assert all(np.isfinite(y) for y in crs.y_limits)
+
+
 def test_specific_lambert():
     # This projection comes from EPSG Projection 3034 - ETRS89 / ETRS-LCC.
     crs = ccrs.LambertConformal(central_longitude=10,