Create Filled Polygon with Matplotlib

Introduction

In this lab, we will learn how to create a filled polygon using Matplotlib in Python. We will use the Koch snowflake as an example polygon.

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Import Libraries

Before we start, let's import the necessary libraries.

import matplotlib.pyplot as plt
import numpy as np

Define the Koch Snowflake Function

Next, we will define a function to generate the Koch snowflake. The function takes two parameters: the recursion depth and the scale factor.

def koch_snowflake(order, scale=10):
    """
    Return two lists x, y of point coordinates of the Koch snowflake.

    Parameters
    ----------
    order : int
        The recursion depth.
    scale : float
        The extent of the snowflake (edge length of the base triangle).
    """
    def _koch_snowflake_complex(order):
        if order == 0:
            ## initial triangle
            angles = np.array([0, 120, 240]) + 90
            return scale / np.sqrt(3) * np.exp(np.deg2rad(angles) * 1j)
        else:
            ZR = 0.5 - 0.5j * np.sqrt(3) / 3

            p1 = _koch_snowflake_complex(order - 1)  ## start points
            p2 = np.roll(p1, shift=-1)  ## end points
            dp = p2 - p1  ## connection vectors

            new_points = np.empty(len(p1) * 4, dtype=np.complex128)
            new_points[::4] = p1
            new_points[1::4] = p1 + dp / 3
            new_points[2::4] = p1 + dp * ZR
            new_points[3::4] = p1 + dp / 3 * 2
            return new_points

    points = _koch_snowflake_complex(order)
    x, y = points.real, points.imag
    return x, y

Generate a Filled Polygon

Now, we can generate a filled polygon using the fill() function. We will use the Koch snowflake function to generate the coordinates for the polygon.

x, y = koch_snowflake(order=5)

plt.figure(figsize=(8, 8))
plt.axis('equal')
plt.fill(x, y)
plt.show()

Customize the Polygon

We can customize the colors and linewidth of the polygon using keyword arguments in the fill() function.

x, y = koch_snowflake(order=2)

fig, (ax1, ax2, ax3) = plt.subplots(1, 3, figsize=(9, 3),
                                    subplot_kw={'aspect': 'equal'})
ax1.fill(x, y)
ax2.fill(x, y, facecolor='lightsalmon', edgecolor='orangered', linewidth=3)
ax3.fill(x, y, facecolor='none', edgecolor='purple', linewidth=3)

plt.show()

Summary

In this lab, we learned how to create a filled polygon using Matplotlib in Python. We used the Koch snowflake as an example polygon and demonstrated how to customize the polygon with different colors and linewidths.