To add a cursor to a curve in Matplotlib, we can take the following steps −
- Set the figure size and adjust the padding between and around the subplots.
- Create t and s data points using numpy.
- Create a figure and a set of subplots.
- Get the cursor class instance, to update the cursor points on the plot.
- In mouse_event, get the x and y data of the current position of the mouse.
- Get the x and y data points' indices.
- Set the x and y positions.
- Set the text position and redraw agg buffer and mouse event.
- Plot t and s data points using plot() method.
- Set some axis properties.
- To display the figure, use show() method.
Example
import matplotlib.pyplot as plt import numpy as np plt.rcParams["figure.figsize"] = [7.50, 3.50] plt.rcParams["figure.autolayout"] = True class CursorClass(object): def __init__(self, ax, x, y): self.ax = ax self.ly = ax.axvline(color='yellow', alpha=0.5) self.marker, = ax.plot([0], [0], marker="o", color="red", zorder=3) self.x = x self.y = y self.txt = ax.text(0.7, 0.9, '') def mouse_event(self, event): if event.inaxes: x, y = event.xdata, event.ydata indx = np.searchsorted(self.x, [x])[0] x = self.x[indx] y = self.y[indx] self.ly.set_xdata(x) self.marker.set_data([x], [y]) self.txt.set_text('x=%1.2f, y=%1.2f' % (x, y)) self.txt.set_position((x, y)) self.ax.figure.canvas.draw_idle() else: return t = np.arange(0.0, 1.0, 0.01) s = np.sin(2 * 2 * np.pi * t) fig, ax = plt.subplots() cursor = CursorClass(ax, t, s) cid = plt.connect('motion_notify_event', cursor.mouse_event) ax.plot(t, s, lw=2, color='green') plt.axis([0, 1, -1, 1]) plt.show()