Create Polar Graphs with Python Matplotlib

Introduction

In this lab, you will learn how to create a polar graph and annotate it using Python Matplotlib library. A polar graph is a graph drawn using polar coordinates. It is useful for visualizing cyclic phenomena such as waves, seasons, and tides.

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Import Libraries

To get started, we first need to import the necessary libraries. In this case, we need numpy and matplotlib.

import matplotlib.pyplot as plt
import numpy as np

Create a Polar Graph

Next, we create a polar graph by defining the figure and specifying that it has a polar projection. We also define the radius and theta values to be used in plotting.

fig = plt.figure()
ax = fig.add_subplot(projection='polar')
r = np.arange(0, 1, 0.001)
theta = 2 * 2*np.pi * r
line, = ax.plot(theta, r, color='#ee8d18', lw=3)

Add Annotation

We can add an annotation to the polar graph by specifying the location of the annotation. In this case, we choose a specific point on the graph and annotate it.

ind = 800
thisr, thistheta = r[ind], theta[ind]
ax.plot([thistheta], [thisr], 'o')
ax.annotate('a polar annotation',
            xy=(thistheta, thisr),  ## theta, radius
            xytext=(0.05, 0.05),    ## fraction, fraction
            textcoords='figure fraction',
            arrowprops=dict(facecolor='black', shrink=0.05),
            horizontalalignment='left',
            verticalalignment='bottom',
            )

Display the Graph

We can now display the graph using plt.show().

plt.show()

Summary

In this lab, we learned how to create a polar graph and annotate it using Python Matplotlib library. We used numpy to define the radius and theta values and plt.annotate() to add an annotation to the graph. We also displayed the graph using plt.show().