convert Array of polygons to Multipolygon

Question

I have an array of Polygons. I need to convert the array in to Multipolygon.

["POLYGON ((-93.8153401599999 31.6253224010001, -93.8154545089999 31.613245482, -93.8256952309999 31.6133096470001, -93.8239846819999 31.6142335050001, -93.822649241 31.614534889, -93.819589744 31.6141266810001, -93.8187199179999 31.6145615630001, -93.818796329 31.6166099970001, -93.8191396409999 31.616805696, -93.822160944 31.6185287610001, -93.8259606669999 31.6195415540001, -93.827173805 31.6202834370001, -93.826861 31.621054014, -93.826721397 31.6210996090001, -93.825838469 31.621387795, -93.823763302 31.620645804, -93.8224278609999 31.620880388, -93.8207344099999 31.6214468590001, -93.817712918 31.621645233, -93.8171636009999 31.6218779230001, -93.8170138 31.622175612, -93.816896795 31.622408104, -93.816843193 31.622514901, -93.8172703129999 31.623758464, -93.817027909 31.6250143240001, -93.816942408 31.624910524, -93.8153401599999 31.6253224010001))", "POLYGON ((-93.827875499 31.6135011530001, -93.8276549939999 31.6133218590001, -93.830593683 31.613340276, -93.827860513 31.616556659, -93.825911348 31.6159317660001, -93.825861447 31.615915767, -93.826296355 31.6149087000001, -93.8272805829999 31.614407122, -93.827341685 31.6143140250001, -93.827875499 31.6135011530001))"]

I am using the following code to convert the Multipolygons using Apache Sedona

select FID,ST_Multi(ST_GeomFromText(collect_list(polygon))) polygon_list group by 1

I am getting the error like "org.apache.spark.sql.catalyst.util.GenericArrayData cannot be cast to org.apache.spark.unsafe.types.UTF8String" .How can I overcome this issue ? is the same thing can be achieved using Geopandas or shapely?

score 1 · Answer 1 · answered Sep 05 '22 at 13:27

a MultiPolygon is just a list of Polygon, so you need to reconstruct every Polygon in a list and then pass it to MultiPolygon.

With the format of the string you gave, I got it to work like that :

from shapely.geometry import Polygon, MultiPolygon

poly_string = ["POLYGON ((-93.8153401599999 31.6253224010001, -93.8154545089999 31.613245482, -93.8256952309999 31.6133096470001, -93.8239846819999 31.6142335050001, -93.822649241 31.614534889, -93.819589744 31.6141266810001, -93.8187199179999 31.6145615630001, -93.818796329 31.6166099970001, -93.8191396409999 31.616805696, -93.822160944 31.6185287610001, -93.8259606669999 31.6195415540001, -93.827173805 31.6202834370001, -93.826861 31.621054014, -93.826721397 31.6210996090001, -93.825838469 31.621387795, -93.823763302 31.620645804, -93.8224278609999 31.620880388, -93.8207344099999 31.6214468590001, -93.817712918 31.621645233, -93.8171636009999 31.6218779230001, -93.8170138 31.622175612, -93.816896795 31.622408104, -93.816843193 31.622514901, -93.8172703129999 31.623758464, -93.817027909 31.6250143240001, -93.816942408 31.624910524, -93.8153401599999 31.6253224010001))", "POLYGON ((-93.827875499 31.6135011530001, -93.8276549939999 31.6133218590001, -93.830593683 31.613340276, -93.827860513 31.616556659, -93.825911348 31.6159317660001, -93.825861447 31.615915767, -93.826296355 31.6149087000001, -93.8272805829999 31.614407122, -93.827341685 31.6143140250001, -93.827875499 31.6135011530001))"]

polygons = []
for poly in  poly_string:
    coordinates = []
    for s in poly.split('('):
        if len(s.split(')')) > 1:
            for c in s.split(')')[0].split(','):
                coordinates.append((float(c.lstrip().split(' ')[0]),
                                    float(c.lstrip().split(' ')[1]))) 
            polygons.append(Polygon(coordinates))

multipoly = MultiPolygon(polygons)

The resulting MultiPolygon looks like that :

score 1 · Accepted Answer · answered Sep 06 '22 at 10:36

The answer given by @Antoine B is a very good attempt. But it won't work with the polygons that have hole(s) in them. There is another approach that works with such polygons, and the code is easier to comprehend.

from shapely.geometry import Polygon, MultiPolygon
from shapely import wkt
from shapely.wkt import loads

# List of strings representing polygons
poly_string = ["POLYGON ((-93.8153401599999 31.6253224010001, -93.8154545089999 31.613245482, -93.8256952309999 31.6133096470001, -93.8239846819999 31.6142335050001, -93.822649241 31.614534889, -93.819589744 31.6141266810001, -93.8187199179999 31.6145615630001, -93.818796329 31.6166099970001, -93.8191396409999 31.616805696, -93.822160944 31.6185287610001, -93.8259606669999 31.6195415540001, -93.827173805 31.6202834370001, -93.826861 31.621054014, -93.826721397 31.6210996090001, -93.825838469 31.621387795, -93.823763302 31.620645804, -93.8224278609999 31.620880388, -93.8207344099999 31.6214468590001, -93.817712918 31.621645233, -93.8171636009999 31.6218779230001, -93.8170138 31.622175612, -93.816896795 31.622408104, -93.816843193 31.622514901, -93.8172703129999 31.623758464, -93.817027909 31.6250143240001, -93.816942408 31.624910524, -93.8153401599999 31.6253224010001))", "POLYGON ((-93.827875499 31.6135011530001, -93.8276549939999 31.6133218590001, -93.830593683 31.613340276, -93.827860513 31.616556659, -93.825911348 31.6159317660001, -93.825861447 31.615915767, -93.826296355 31.6149087000001, -93.8272805829999 31.614407122, -93.827341685 31.6143140250001, -93.827875499 31.6135011530001))"]

# Create a list of polygons from the list of strings
all_pgons = [loads(pgon) for pgon in poly_string]

# Create the required multipolygon
multi_pgon = MultiPolygon(all_pgons)

This is a list of strings of polygons with holes.

# List of polygons with hole
poly_string = ['POLYGON ((1 2, 1 5, 4 4, 1 2), (1.2 3, 3 4, 1.3 4, 1.2 3))', 
               'POLYGON ((11 12, 11 15, 14 14, 11 12), (11.2 13, 13 14, 11.3 14, 11.2 13))']

The code above also works well in this case.

score 0 · Answer 3 · answered Sep 05 '22 at 19:22

0

I would try

select 
  FID, 
  ST_Multi(ST_Collect(ST_GeomFromText(polygon))) polygon_list 
group by 1

answered Sep 05 '22 at 19:22

Michael Entin

7,189
3
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ST_GeomFromText is not accepting generic array . – code_bug Sep 06 '22 at 08:28

convert Array of polygons to Multipolygon

3 Answers3