Testing shapely's simplify operation while preserving topology and resulting in an invalid geometry.

test.py

#!/usr/bin/env python

from json import loads

from shapely import speedups
speedups.available and speedups.enable()

from shapely.geometry import shape

from numpy import asarray
from matplotlib import pyplot as plt


def plot_polygon(g):
    a = asarray(g.exterior)
    plt.plot(a[:, 0], a[:, 1])


def plot_multipolygon(g):
    for g in g.geoms:
        plot_polygon(g)


def plot_geometry(g):
    if g.type == "MultiPolygon":
        plot_multipolygon(g)
    elif g.type == "Polygon":
        plot_polygon(g)


geom = shape(loads(open("test.json", "r").read()))

print "geom.is_valid: {0:s}".format(repr(geom.is_valid))

if not geom.is_valid:
    geom = geom.buffer(0.0)

print "geom.is_valid: {0:s}".format(repr(geom.is_valid))

plot_geometry(geom)
plt.show()
plt.clf()

geom = geom.simplify(0.05)
print "geom.is_valid: {0:s}".format(repr(geom.is_valid))

plot_geometry(geom)
plt.show()
plt.clf()