GeoPandas Spatial Join with random samples

Question

I have a geopandas DataFrame with Polygon geometry and another one with POINT geometry. I'd like to do a spatial join between them and randomly select a set of points that are within certain distance or close to the polygon.

Here's some sample data:

https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=2c3c5863af9fe855491e4ef71f21a64b

Criteria:

Select n randomly sampled points from top m nearest points between gpd2.geometry (Point) to each gpd1.geometry (Polygon).

import geopandas as gpd
import numpy as np

gpd_merged = gpd.sjoin(
                       gpd1, # polygon geometry
                       gpd2, # point geometry (randomly sample and join) 
                       how = 'left',
                       distance_col = "distances"
                      )

Can you also provide those points as you did with polygons ? — Taras
– Taras ♦, Commented Jun 15, 2022 at 7:42
Welcome to gis.stackexchange! Please note that a good question on this site is expected to show some degree of research on your part, i.e. what you have tried and - if applicable - code so far. For more info, you can check our faq. — underdark
– underdark, Commented Jun 15, 2022 at 18:50

user2856 · Accepted Answer · 2022-07-25 13:10:47Z

The following will randomly sample n points within a specified distance of each poly.

It uses gpd.sjoin_nearest to assign all points to the closest polygon within a certain distance, then groupby and sample to randomly select the desired number of points per polygon.

import geopandas as gpd

gdf_points = gpd.read_file(points)
gdf_poly = gpd.read_file(polys)

max_distance = 0.1
n_points = 3

gdf_randomsample = gpd.sjoin_nearest(
    gdf_points,       # point geometry
    gdf_poly,         # polygon geometry
    how='inner',      # drop points outside max_distance
    max_distance=max_distance
).groupby("id_right").sample(n=n_points)

Here's an example with your polygons (the buffer represents the specified max distance):

But note that the little polygon "ID" 2 gets no points assigned to it as all points are closer to the other polygons.

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