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