def main():
# Define the two coordinate systems with different ellipses.
wgs84 = ccrs.PlateCarree(globe=ccrs.Globe(datum='WGS84', ellipse='WGS84'))
sphere = ccrs.PlateCarree(
globe=ccrs.Globe(datum='WGS84', ellipse='sphere'))
# Define the coordinate system of the data we have from Natural Earth and
# acquire the 1:10m physical coastline shapefile.
geodetic = ccrs.Geodetic(globe=ccrs.Globe(datum='WGS84'))
dataset = cfeature.NaturalEarthFeature(category='physical',
name='coastline',
scale='10m')
# Create a Stamen map tiler instance, and use its CRS for the GeoAxes.
tiler = StamenTerrain()
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1, projection=tiler.crs)
ax.set_title('The effect of incorrectly referencing the Solomon Islands')
# Pick the area of interest. In our case, roughly the Solomon Islands, and
# get hold of the coastlines for that area.
extent = [155, 163, -11.5, -6]
ax.set_extent(extent, geodetic)
geoms = list(dataset.intersecting_geometries(extent))
# Add the Stamen aerial imagery at zoom level 7.
ax.add_image(tiler, 7)
# Transform the geodetic coordinates of the coastlines into the two
# projections of differing ellipses.
wgs84_geoms = [
geom_transform(transform_fn_factory(wgs84, geodetic), geom)
for geom in geoms
]
sphere_geoms = [
geom_transform(transform_fn_factory(sphere, geodetic), geom)
for geom in geoms
]
# Using these differently referenced geometries, assume that they are
# both referenced to WGS84.
ax.add_geometries(wgs84_geoms, wgs84, edgecolor='white', color='none')
ax.add_geometries(sphere_geoms, wgs84, edgecolor='gray', color='none')
# Create a legend for the coastlines.
legend_artists = [
Line([0], [0], color=color, linewidth=3) for color in ('white', 'gray')
]
legend_texts = ['Correct ellipse\n(WGS84)', 'Incorrect ellipse\n(sphere)']
legend = ax.legend(legend_artists,
legend_texts,
fancybox=True,
loc='lower left',
framealpha=0.75)
legend.legendPatch.set_facecolor('wheat')
# Create an inset GeoAxes showing the location of the Solomon Islands.
sub_ax = fig.add_axes([0.7, 0.625, 0.2, 0.2],
projection=ccrs.PlateCarree())
sub_ax.set_extent([110, 180, -50, 10], geodetic)
# Make a nice border around the inset axes.
effect = Stroke(linewidth=4, foreground='wheat', alpha=0.5)
sub_ax.outline_patch.set_path_effects([effect])
# Add the land, coastlines and the extent of the Solomon Islands.
sub_ax.add_feature(cfeature.LAND)
sub_ax.coastlines()
extent_box = sgeom.box(extent[0], extent[2], extent[1], extent[3])
sub_ax.add_geometries([extent_box],
ccrs.PlateCarree(),
color='none',
edgecolor='blue',
linewidth=2)
plt.show()
def main():
# Define the two coordinate systems with different ellipses.
wgs84 = ccrs.PlateCarree(globe=ccrs.Globe(datum='WGS84',
ellipse='WGS84'))
sphere = ccrs.PlateCarree(globe=ccrs.Globe(datum='WGS84',
ellipse='sphere'))
# Define the coordinate system of the data we have from Natural Earth and
# acquire the 1:10m physical coastline shapefile.
geodetic = ccrs.Geodetic(globe=ccrs.Globe(datum='WGS84'))
dataset = cfeature.NaturalEarthFeature(category='physical',
name='coastline',
scale='10m')
# Create a Stamen map tiler instance, and use its CRS for the GeoAxes.
tiler = StamenTerrain()
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1, projection=tiler.crs)
ax.set_title('The effect of incorrectly referencing the Solomon Islands')
# Pick the area of interest. In our case, roughly the Solomon Islands, and
# get hold of the coastlines for that area.
extent = [155, 163, -11.5, -6]
ax.set_extent(extent, geodetic)
geoms = list(dataset.intersecting_geometries(extent))
# Add the Stamen aerial imagery at zoom level 7.
ax.add_image(tiler, 7)
# Transform the geodetic coordinates of the coastlines into the two
# projections of differing ellipses.
wgs84_geoms = [geom_transform(transform_fn_factory(wgs84, geodetic),
geom) for geom in geoms]
sphere_geoms = [geom_transform(transform_fn_factory(sphere, geodetic),
geom) for geom in geoms]
# Using these differently referenced geometries, assume that they are
# both referenced to WGS84.
ax.add_geometries(wgs84_geoms, wgs84, edgecolor='white', facecolor='none')
ax.add_geometries(sphere_geoms, wgs84, edgecolor='gray', facecolor='none')
# Create a legend for the coastlines.
legend_artists = [Line([0], [0], color=color, linewidth=3)
for color in ('white', 'gray')]
legend_texts = ['Correct ellipse\n(WGS84)', 'Incorrect ellipse\n(sphere)']
legend = ax.legend(legend_artists, legend_texts, fancybox=True,
loc='lower left', framealpha=0.75)
legend.legendPatch.set_facecolor('wheat')
# Create an inset GeoAxes showing the location of the Solomon Islands.
sub_ax = fig.add_axes([0.7, 0.625, 0.2, 0.2],
projection=ccrs.PlateCarree())
sub_ax.set_extent([110, 180, -50, 10], geodetic)
# Make a nice border around the inset axes.
effect = Stroke(linewidth=4, foreground='wheat', alpha=0.5)
sub_ax.outline_patch.set_path_effects([effect])
# Add the land, coastlines and the extent of the Solomon Islands.
sub_ax.add_feature(cfeature.LAND)
sub_ax.coastlines()
extent_box = sgeom.box(extent[0], extent[2], extent[1], extent[3])
sub_ax.add_geometries([extent_box], ccrs.PlateCarree(), facecolor='none',
edgecolor='blue', linewidth=2)
plt.show()
