import random
import unittest
from functools import partial
from itertools import islice
import pytest
from shapely.geometry import MultiPolygon, Point
from shapely.ops import unary_union
def halton(base):
"""Returns an iterator over an infinite Halton sequence"""
def value(index):
result = 0.0
f = 1.0 / base
i = index
while i > 0:
result += f * (i % base)
i = i // base
f = f / base
return result
i = 1
while i > 0:
yield value(i)
i += 1
class UnionTestCase(unittest.TestCase):
def test_unary_union_partial(self):
# Use a partial function to make 100 points uniformly distributed
# in a 40x40 box centered on 0,0.
r = partial(random.uniform, -20.0, 20.0)
points = [Point(r(), r()) for i in range(100)]
# Buffer the points, producing 100 polygon spots
spots = [p.buffer(2.5) for p in points]
# Perform a cascaded union of the polygon spots, dissolving them
# into a collection of polygon patches
u = unary_union(spots)
assert u.geom_type in ("Polygon", "MultiPolygon")
def setUp(self):
# Instead of random points, use deterministic, pseudo-random Halton
# sequences for repeatability sake.
self.coords = zip(
list(islice(halton(5), 20, 120)),
list(islice(halton(7), 20, 120)),
)
def test_unary_union(self):
patches = [Point(xy).buffer(0.05) for xy in self.coords]
u = unary_union(patches)
assert u.geom_type == "MultiPolygon"
assert u.area == pytest.approx(0.718572540569)
def test_unary_union_multi(self):
# Test of multipart input based on comment by @schwehr at
# https://github.com/shapely/shapely/issues/47#issuecomment-21809308
patches = MultiPolygon([Point(xy).buffer(0.05) for xy in self.coords])
assert unary_union(patches).area == pytest.approx(0.71857254056)
assert unary_union([patches, patches]).area == pytest.approx(0.71857254056)