4.8. Graphical input#

Matplotlib provides extensive options to interact with figures. One of the most helpful (and also the most basic) is plt.ginput. It lets the user click on a number of points on the figure, and then returns these coordinates. For instance, these instructions:

import matplotlib.pyplot as plt

plt.plot([0.0, 1.0, -1.0, 2.0, 0.5, 0.0])
points = plt.ginput(10)  # 10 points

generate Fig. 4.3 and let the user click a maximum of 10 points.

plt.ginput -width:wider

Fig. 4.3 Clicking and retrieving coordinates using plt.ginput.#

  • Left-click adds a point (red cross);

  • Right-click removes the last added point;

  • Middle-click stops and returns the current points.

Points are returned as a list of (x, y) tuples.

[(0.44858870967741926, 0.003571428571428781),
 (1.1693548387096775, 0.42321428571428577),
 (2.089717741935484, 0.6107142857142862),
 (3.5756048387096775, 0.8339285714285718)]