Matplotlib | Color Intersecting Lines | Programming Tutorial

Introduction

In this lab, we will learn how to change the colors of lines intersecting a rectangle using the .intersects_bbox function from Matplotlib. We will create a rectangle and generate random lines that intersect it. Then, we will change the color of the intersecting lines to red and the remaining lines to blue.

VM Tips

After the VM startup is done, click the top left corner to switch to the Notebook tab to access Jupyter Notebook for practice.

Sometimes, you may need to wait a few seconds for Jupyter Notebook to finish loading. The validation of operations cannot be automated because of limitations in Jupyter Notebook.

If you face issues during learning, feel free to ask Labby. Provide feedback after the session, and we will promptly resolve the problem for you.

Import the required libraries

We will import matplotlib.pyplot and numpy libraries to create the rectangle and generate random lines.

import matplotlib.pyplot as plt
import numpy as np

Set up the rectangle

We will define the position and dimensions of the rectangle using left, bottom, width, and height variables. Then, we will create the rectangle using Rectangle class and add it to the plot using add_patch method.

left, bottom, width, height = (-1, -1, 2, 2)
rect = plt.Rectangle((left, bottom), width, height,
                     facecolor="black", alpha=0.1)

fig, ax = plt.subplots()
ax.add_patch(rect)

Generate random lines

We will generate 12 random lines using numpy library and plot them using plot method. If a line intersects the rectangle, its color will be red, otherwise blue. We will use Path class to create a line and intersects_bbox method to check if it intersects the rectangle.

bbox = Bbox.from_bounds(left, bottom, width, height)

for i in range(12):
    vertices = (np.random.random((2, 2)) - 0.5) * 6.0
    path = Path(vertices)
    if path.intersects_bbox(bbox):
        color = 'r'
    else:
        color = 'b'
    ax.plot(vertices[:, 0], vertices[:, 1], color=color)

Display the plot

We will display the plot using show method.

plt.show()

Summary

In this lab, we learned how to change the colors of lines intersecting a rectangle using the .intersects_bbox function from Matplotlib. We created a rectangle and generated random lines that intersected it. Then, we changed the color of the intersecting lines to red and the remaining lines to blue.

Changing Line Colors of a Rectangle