[英]Count Points in Polygon and write result to (Geo)Dataframe
I want to count how many points there are per Polygon我想计算每个多边形有多少点
# Credits of this code go to: https://stackoverflow.com/questions/69642668/the-indices-of-the-two-geoseries-are-different-understanding-indices/69644010#69644010
import pandas as pd
import numpy as np
import geopandas as gpd
import shapely.geometry
import requests
# source some points and polygons
# fmt: off
dfp = pd.read_html("https://www.latlong.net/category/cities-235-15.html")[0]
dfp = gpd.GeoDataFrame(dfp, geometry=dfp.loc[:,["Longitude", "Latitude",]].apply(shapely.geometry.Point, axis=1))
res = requests.get("https://opendata.arcgis.com/datasets/69dc11c7386943b4ad8893c45648b1e1_0.geojson")
df_poly = gpd.GeoDataFrame.from_features(res.json())
# fmt: on
Now I sjoin
the two.现在我
sjoin
两个。 I use df_poly
first, in order to add the points dfp
to the GeoDataframe
df_poly
.我首先使用
df_poly
,以便将点dfp
添加到GeoDataframe
df_poly
。
df_poly.sjoin(dfp)
Now I want to count how many points
there are per polygon
.现在我想计算每个
polygon
有多少points
。 I thought我想
df_poly.sjoin(dfp).groupby('OBJECTID').count()
But that does not add a column
to the GeoDataframe
df_poly
with the count
of each group
.但这不会向
GeoDataframe
df_poly
添加一column
,其中GeoDataframe
每个group
的count
。
You need to add one of the columns from the output of count()
back into the original DataFrame using merge.您需要使用合并将
count()
的输出中的一列添加回原始 DataFrame。 I have used the geometry column and renamed it to n_points
:我使用了几何列并将其重命名为
n_points
:
df_poly.merge(
df_poly.sjoin(
dfp
).groupby(
'OBJECTID'
).count().geometry.rename(
'n_points'
).reset_index())
This is a follow on to this question The indices of the two GeoSeries are different - Understanding Indices这是这个问题的后续两个 GeoSeries 的索引不同 - 理解索引
gpd.sjoin(dfp, df_poly).groupby("index_right").size().rename("points")
can then be simply joined to the polygon GeoDataFrame to give how many points were foundgpd.sjoin(dfp, df_poly).groupby("index_right").size().rename("points")
然后可以简单地加入多边形GeoDataFrame以给出找到的点数how="left"
to ensure it's a left join, not an inner join.how="left"
以确保它是左连接,而不是内部连接。 Any polygons with no points with have NaN
you may want to fillna(0)
in this case.NaN
您可能想要fillna(0)
。import pandas as pd
import numpy as np
import geopandas as gpd
import shapely.geometry
import requests
# source some points and polygons
# fmt: off
dfp = pd.read_html("https://www.latlong.net/category/cities-235-15.html")[0]
dfp = pd.concat([dfp,dfp]).reset_index(drop=True)
dfp = gpd.GeoDataFrame(dfp, geometry=dfp.loc[:,["Longitude", "Latitude",]].apply(shapely.geometry.Point, axis=1))
res = requests.get("https://opendata.arcgis.com/datasets/69dc11c7386943b4ad8893c45648b1e1_0.geojson")
df_poly = gpd.GeoDataFrame.from_features(res.json())
# fmt: on
df_poly.join(
gpd.sjoin(dfp, df_poly).groupby("index_right").size().rename("points"),
how="left",
)
Building on the answere Fergus McClean provided, this can even be done in less code:基于 Fergus McClean 提供的答案,这甚至可以用更少的代码完成:
df_poly.merge(df_poly.sjoin(dfp).groupby('OBJECTID').size().rename('n_points').reset_index())
However, the method ( .join()
) proposed by Rob Raymond to combine the two dataframes
keeps the entries that have no count.然而,Rob Raymond 提出的方法 (
.join()
) 将两个dataframes
结合起来,保留了没有计数的条目。
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