How to fill in a shape composed of multiple curves?

Question

I'm attempting to fill in an area enclosed by four curves but can't seem to get the fill I want: I'm using fill_between() but that can only handle two lines at most. Here's the code I currently have:

fig,ax = plt.subplots()
x = np.arange(start = -80,stop = 80,step = 1e-3)
yArc = np.sqrt(80**2 - x**2) 
yLL = -2*x - 10
yRL = 2*x - 10
yTop = 0*x + 150
ax.fill_between(x,yArc,yTop,where = yArc<yTop,color = 'red',alpha = 0.8)
plt.show()

Here's the output: Region of Interest

Note: In case you can't see, there is a horizontal line just about where the free-throw line is.

What is ax ? how did you define it ? – Gustav Rasmussen Jun 11 '20 at 17:22 — Gustav Rasmussen, Jun 11 '20 at 17:22
fig, ax = plt.subplots() ? – Gustav Rasmussen Jun 11 '20 at 17:23 — Gustav Rasmussen, Jun 11 '20 at 17:23

score 0 · Accepted Answer · answered Jun 11 '20 at 17:47

You can use set operations between different filters to fill the central part first,

import numpy as np
import matplotlib.pyplot as plt

fig, ax = plt.subplots()
x = np.arange(start=-80, stop=80, step=1e-3)

yArc = np.sqrt(80 ** 2 - x ** 2)
yLL = -2 * x - 10
yRL = 2 * x - 10
yTop = 0 * x + 150

plt.plot(x, yArc, "r")
plt.plot(x, yLL, "b")
plt.plot(x, yRL, "g")
plt.plot(x, yTop, "k")

filt_1 = yArc < yTop
filt_2 = yArc > yLL
filt_3 = yArc > yRL
filt = filt_1 & filt_2 & filt_3

ax.fill_between(x, yArc, yTop, where=filt, color="orange", alpha=0.8)

plt.show()

Producing:

And finally fill the two remaining right triangles, see for example: matplotlib: use fill_between to make coloured triangles

Legend! I've been trying so many different complex solutions, thanks for the simple one haha. — PM25, Jun 11 '20 at 17:54
Nice :) If you found the answer useful, please consider to mark it as the accepted answer / upvote. — Gustav Rasmussen, Jun 11 '20 at 18:06

score 0 · Answer 2 · answered Jun 11 '20 at 18:00

The most obvious way to tackle this, is to create a bottom curve as the maximum of the three curves:

import numpy as np
import matplotlib.pyplot as plt

fig, ax = plt.subplots()
x = np.arange(start=-80, stop=80, step=1e-3)

yArc = np.sqrt(80 ** 2 - x ** 2)
yLL = -2 * x - 10
yRL = 2 * x - 10
yTop = 0 * x + 150

plt.plot(x, yArc, "r")
plt.plot(x, yLL, "b")
plt.plot(x, yRL, "g")
plt.plot(x, yTop, "k")

yBottom = np.max([yArc, yLL, yRL], axis=0)
ax.fill_between(x, yBottom, yTop, where=yBottom <= yTop, color="orange", alpha=0.8)

Is there any reason you prefer a more complicated solution that leaves out the triangle areas? — JohanC, Jun 14 '20 at 00:03

How to fill in a shape composed of multiple curves?

2 Answers2