Define a circe that circumscribes a set of points (shapefile) in python

I have a shapefile of points, defined by X and Y coordinates, ad the ID feature. I have at least 3 different points with the same ID number.

I would like to define, for each ID, the shapefile of a circle that circumscribes the points.

How can this be done in python environment?

Answer

• there is a library that does it: https://pypi.org/project/miniball/
• it’s pretty forward to integrate in standard pandas pattern https://pandas.pydata.org/pandas-docs/stable/user_guide/groupby.html
• solution really reduces to this:

def circle(points):
    p, r = miniball.get_bounding_ball(np.array([points.x, points.y]).T)
    return shapely.geometry.Point(p).buffer(math.sqrt(r))

col = "group"
# generate circles around groups of points
gdf_c = cities.groupby(col, as_index=False).agg(geometry=("geometry", circle))

• with sample example and visualisation, circles do become distorted due to epsg:4326 projection limitations

full working example

import geopandas as gpd
import numpy as np
import shapely
import miniball
import math
import pandas as pd

cities = gpd.read_file(gpd.datasets.get_path("naturalearth_cities"))
world = gpd.read_file(gpd.datasets.get_path("naturalearth_lowres"))

# a semi-synthetic grouping of cities
world["size"] = world.groupby("continent")["pop_est"].apply(
    lambda d: pd.cut(d, 2, labels=list("ab"), duplicates="drop").astype(str)
)
cities = cities.sjoin(world.loc[:, ["continent", "iso_a3", "size", "geometry"]])
cities["group"] = cities["continent"] + cities["size"]


def circle(points):
    p, r = miniball.get_bounding_ball(np.array([points.x, points.y]).T)
    return shapely.geometry.Point(p).buffer(math.sqrt(r))

col = "group"
# generate circles around groups of points
gdf_c = cities.groupby(col, as_index=False).agg(geometry=("geometry", circle))

# visualize it
m = cities.explore(column=col, height=300, width=600, legend=False)
gdf_c.loc[~gdf_c["geometry"].is_empty].explore(
    m=m, column=col, marker_kwds={"radius": 20}, legend=False
)

output