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Plot the convex hull around a set of points as a shaded polygon.
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# -*- coding: utf-8 -*- | |
""" | |
Plot the convex hull around a set of points as a | |
shaded polygon. | |
@author: Nicolas Guarin Zapata and Kaiwen | |
@date: February 6, 2023 | |
""" | |
import numpy as np | |
from scipy.spatial import ConvexHull | |
import matplotlib.pyplot as plt | |
from matplotlib.patches import Polygon | |
m = 30 # number of points | |
points = np.random.rand(m, 2) # m random points in 2-D | |
plt.plot(points[:,0], points[:,1], 'o') | |
cent = np.mean(points, 0) | |
# ConvexHull won't work when m < dimension + 1 | |
if m < 2 + 1: # where 2 is dimension | |
# augment the points by sampling around existing points | |
# so that ConvexHull works again | |
r_eps = 0.005 # in what radius to sample | |
n = 50 # how many additional points to sample | |
points = np.concatenate([p + r_eps * np.random.randn(n, 2) for p in points]) | |
hull = ConvexHull(points) | |
pts = points[hull.vertices] # in 2-dimension context, guaranteed in counterclockwise | |
# Plot the polygon | |
k = 1.1 # how large is the polygon in terms of the size of the hull | |
color = 'green' | |
poly = Polygon(k*(pts - cent) + cent, | |
facecolor=color, alpha=0.2, capstyle='round') | |
plt.gca().add_patch(poly) | |
plt.savefig('convex.png') | |
# Above codes (lines 34, 35) can also be written in object-oriented interface as: | |
#fig, ax = plt.subplots() | |
#ax.add_patch(poly) | |
#fig.savefig('convex.png') | |
#plt.close(fig) |
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