CODEWITHSUNDEEP
pythonshapely
Rahul
Rahul

Reputation: 3386

How to extract Polygons from Multipolygons in Shapely?

I'm trying to extract the polygons from multipolygons in Shapely. I can transform a list of polygons into multipolygons using MultiPolygon from Shapely.

>>> Multi = MultiPolygon([shape(pol['geometry']) for pol in fiona.open('data.shp')])

And,

>>> Multi.wkt
'MULTIPOLYGON (((249744.2315302934148349 142798.1643468967231456, 250113.7910872535139788 142132.9571443685272243, 250062.6213024436729029 141973.7622582934272941, 249607.7787708004761953 141757.7120557629095856, 249367.7742475979903247 142304.6840291862317827, 249367.7742475979903247 142304.6840291862317827, 249744.2315302934148349 142798.1643468967231456)), 
               ((249175.7899173096520826 142292.5352640640921891, 249367.7742475979903247 142304.6840291862317827, 249607.7787708004761953 141757.7120557629095856, 249014.4539607730694115 141876.1348429077770561, 249175.7899173096520826 142292.5352640640921891)))'

Does anybody know how can I reverse the process i.e. given a multipolygon how can I convert it to separate polygons?

Upvotes: 29

Views: 68556

Answers (5)

pmav99
pmav99

Reputation: 2057

shapely.get_parts() docs is the fastest way:

>>> print(multipolygon)
<MULTIPOLYGON (((19.652 39.714, 19.652 39.714, 19.652 39.714, 19.652 39.714,...>

>>> shapely.get_num_geometries(mmm)
Out[186]: np.int32(5457)

>>> %timeit list(multipolygon.geoms)
32.5 ms ± 388 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
    runtime: 2.64 s

>>> %timeit shapely.get_parts(multipolygon)
1.9 ms ± 12.8 μs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)

Upvotes: 0

zabop
zabop

Reputation: 7852

To avoid Deprecation Warning when using this othwerwise ok answer, do:

Polygons = list(Multipolygon.geoms)

Upvotes: 33

Andoni Aranguren
Andoni Aranguren

Reputation: 71

As other have already noted from shapely 1.8 onwards iterating upon the Multipolygon class is deprecated. The following code will work in 1.8 but won't in 2.0.

for poly in multipolygon:
  print(poly)

The correct way of doing it since 2.0 as follows:

for poly in multipolygon.geoms:
  print(poly)

Also if you are not specifically iterating through the polygons it might have to do with other libraries being outdated and calling a shapely 2.0 version.

Upvotes: 1

Georgy
Georgy

Reputation: 13697

According to documentation on collections, which include such classes as MultiPoint, MultiLineString and MultiPolygon, their members can be "accessed via the geoms property or via the iterator protocol using in or list()":

from shapely.geometry import MultiPolygon, Polygon

multipolygon = MultiPolygon([Polygon([(0, 0), (1, 1), (1, 0)]),
                             Polygon([(0, 0), (1, 1), (0, 1)])])

polygons = list(multipolygon)
print(*polygons)
# POLYGON ((0 0, 1 1, 1 0, 0 0)) POLYGON ((0 0, 1 1, 0 1, 0 0))

polygons = list(multipolygon.geoms)
print(*polygons)
# POLYGON ((0 0, 1 1, 1 0, 0 0)) POLYGON ((0 0, 1 1, 0 1, 0 0))

for polygon in multipolygon:  # same for multipolygon.geoms
    print(polygon)
# POLYGON ((0 0, 1 1, 1 0, 0 0))
# POLYGON ((0 0, 1 1, 0 1, 0 0))

You can also extract individual geometries by their index:

print(multipolygon[0])
POLYGON ((0 0, 1 1, 1 0, 0 0))

Slicing them will give you a collection though:

print(multipolygon[:1])
MULTIPOLYGON (((0 0, 1 1, 1 0, 0 0)))

Upvotes: 22

Nbarjest
Nbarjest

Reputation: 761

Simply do 

Polygons = list(Multi)

This extracts the polygons and puts them in a list.

Upvotes: 38

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