CODEWITHSUNDEEP
pythonmatplotlib
Bryce Thomas
Bryce Thomas

Reputation: 10799

matplotlib: how to plot concentric circles at a given set of radii

I would like to plot concentric circles at a given set of distances away from a source. The first thing I tried to do was draw an arc on polar plot, as this seemed like a logical substep:

import numpy as np
import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111, polar=True)
ax.plot([1.0,1.5], [5,5], color='r', linestyle='-')
plt.show()

The first problem I'm having is that this draws a straight line rather than an arc:

polar with straight line

So the subquestion might be how do I draw an arc, in this case a 360 degree arc, at a given radius on a polar plot?. On the other hand, there might be a better solution altogether, perhaps one that doesn't involve a polar plot. Ultimately, as per the title, my objective is to draw concentric circles at a set of radii around a centre source.

Upvotes: 3

Views: 7917

Answers (1)

CT Zhu
CT Zhu

Reputation: 54340

easy, use it to make shooting targets all the time.:

ax.plot(np.linspace(0, 2*np.pi, 100), np.ones(100)*5, color='r', linestyle='-')

Just think of how you define a circle in a polar axis? Need two things, angle and radius. Those are np.linspace(0, 2*np.pi, 100) and np.ones(100)*5 here. If you just need a arc, change the first argument to something less than 0 to 2pi. And change the 2nd argument accordingly.

enter image description here There are other ways to do this. plot() creates .lines.Line2D object objects, if you want .collections.PathCollection object instead of Line2D:

ax.scatter(1, 0, s=100000, facecolors='none')

Or you want to make patches:

ax.bar(0, 5, 2*np.pi, bottom=0.0, facecolor='None') #need to modified the edge lines or won't look right

Upvotes: 5

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