How to Plot a Circle in Matplotlib

  1. matplotlib.patches.Circle() Method to Plot a Circle in Matplotlib
  2. Circle Equation to Plot a Circle in Matplotlib
  3. Scatter Plot of Points

To plot a circle in Matplotlib, we can use any of the following methods:

  • matplotlib.patches.Circle() method
  • Circle Equation
  • Scatter plot of points

matplotlib.patches.Circle() Method to Plot a Circle in Matplotlib

Syntax:

matplotlib.patches.Circle((x, y), r=5, **kwargs)

Where,(x, y) is the center of the circle and r is the radius with a default value of 5.

We need to add a circle to axes with the add_artist method as Circle is a subclass of Artist.

import matplotlib.pyplot as plt

figure, axes = plt.subplots()
draw_circle = plt.Circle((0.5, 0.5), 0.3)

axes.set_aspect(1)
axes.add_artist(draw_circle)
plt.title('Circle')
plt.show()

Plot circle with matplotlib.patches.Circle() method

To plot a circle without filling color, we should set the fill parameter to be False.

import matplotlib.pyplot as plt

figure, axes = plt.subplots()
draw_circle = plt.Circle((0.5, 0.5), 0.3,fill=False)

axes.set_aspect(1)
axes.add_artist(draw_circle)
plt.title('Circle')
plt.show()

Plot circle with matplotlib.patches.Circle() method without filling color

We can make the above code simpler by quickly plugging circle into an existing plot with the help of gcf() and gca() functions.

import matplotlib.pyplot as plt

figure, axes = plt.subplots()
draw_circle = plt.Circle((0.5, 0.5), 0.3,fill=False)

plt.gcf().gca().add_artist(draw_circle)
plt.title('Circle')
axes.set_aspect(1)
plt.show()

Plot circle simpler

Circle Equation to Plot a Circle in Matplotlib

Parametric Equation of Circle

The parametric equation of circle is x=r*cos(theta) and y=r*sin(theta).

import numpy as np
import matplotlib.pyplot as plt

theta = np.linspace(0, 2*np.pi, 100)

radius = 0.3

a = radius*np.cos(theta)
b = radius*np.sin(theta)

figure, axes = plt.subplots(1)

axes.plot(a, b)
axes.set_aspect(1)

plt.title('Circle using Parametric Equation')
plt.show()

plot circle with parametric equation of circle

Center-Radius Form of the Circle Equation

We can also plot circle using the center-radius form of the circle equation.

import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(-0.5, 0.5, 100)
y = np.linspace(-0.5, 0.5, 100)

a, b = np.meshgrid(x,y)

C = a**2+b**2-0.2

figure, axes = plt.subplots()

axes.contour(a,b,C,[0])
axes.set_aspect(1)

plt.show()

plot circle with general equation of circle

Scatter Plot of Points

We can also draw a circle in Matplotlib using scatter() method and adjust radius using s parameter. The area of the circle is pi/4*s.

import matplotlib.pyplot as plt

plt.scatter(0, 0, s=4000)
plt.title('Circle')

plt.xlim(-0.75,0.75)
plt.ylim(-0.75,0.75)

plt.show()

Plot circle with scatter plot