matplotlib: fill circular sector between two curves in a polar plot

Question

So I have two curves theta1(r) and theta2(r), where r is uniformly spaced between some two numbers (1 and 330 in this case). How can I fill the radial segment between the two curves?

I have considered adapting this solution, but it does not seem useful out of the box. Provided solution relies on an inverse relation, r(theta), which would be ambiguous and thus inapplicable in my case.

Answer 1

One option is to make a Polygon of the circular sector

import matplotlib.pyplot as plt
from matplotlib.patches import Polygon
import numpy as np


fig, ax = plt.subplots(subplot_kw=dict(projection="polar"))

n = 330
r = np.arange(330)

# auto correlate random numbers (see comment below)
a = np.zeros(n) + np.add.accumulate(np.random.normal(0, np.pi / 180, size=n))
b = np.ones(n) * np.pi / 2 + np.add.accumulate(np.random.normal(0, np.pi / 180, size=n))

ax.plot(a, r)
ax.plot(b, r)

arc_theta = np.linspace(a[-1], b[-1], 101)
arc_r = np.ones_like(arc_theta) * 330

start = np.c_[a, r]
arc = np.c_[arc_theta, arc_r]
end = np.c_[b, r][::-1]

verts = np.concatenate([start, arc, end])

p = Polygon(verts, fc="purple", alpha=0.5)
ax.add_artist(p)

plt.show()

gives