Alpha Shapes with GeoPandas GeoDataFrame

This example opens a shapefile with GeoPandas, and generates a new GeoDataFrame with the alpha shape as its only geometry. It then plots the geodataframe with cartopy.

 import os
 import matplotlib.pyplot as plt
 import cartopy.crs as ccrs
 import geopandas
 import alphashape

 try:
     DATA = os.path.abspath(os.path.join(os.path.dirname(__file__), 'data'))
 except NameError:
     DATA = os.path.abspath(os.path.join(os.path.dirname(os.getcwd()),
                                         'examples', 'data'))

 # Define input points
 gdf = geopandas.read_file(os.path.join(DATA, 'Public_Airports_March2018.shp'))

 # Generate the alpha shape
 alpha_shape = alphashape.alphashape(gdf)

 # Initialize plot
 ax = plt.axes(projection=ccrs.PlateCarree())

 # Plot input points
 gdf_proj = gdf.to_crs(ccrs.Robinson().proj4_init)
 ax.scatter([p.x for p in gdf_proj['geometry']],
            [p.y for p in gdf_proj['geometry']],
            transform=ccrs.Robinson())

 # Plot alpha shape
 ax.add_geometries(
     alpha_shape.to_crs(ccrs.Robinson().proj4_init)['geometry'],
     crs=ccrs.Robinson(), alpha=.2)

 plt.show()