How to add legend on matplotlib animations?-CodePudding

I have a animation of an orbit written in python. I want a legend that the label is a time "dt". This time updates (increases) along the orbit. For example, in the first frame of the gif the legend should be "dt", in the second, dt dt and so on. I tried something that didn't work. Maybe I'm not using the correct commands. The error that appearas: TypeError: __init__() got multiple values for argument 'frames' . Does someone know how to do this legend? The code is above.

fig = plt.figure()

plt.xlabel("x (km)")
plt.ylabel("y (km)")
plt.gca().set_aspect('equal')
ax = plt.axes()
ax.set_facecolor("black")
circle = Circle((0, 0), rs_sun, color='dimgrey')
plt.gca().add_patch(circle)
plt.axis([-(rs_sun / 2.0) / u1 , (rs_sun / 2.0) / u1 , -(rs_sun / 2.0) / u1 , (rs_sun / 2.0) / u1 ])

# Legend

dt = 0.01

leg = [ax.plot(loc = 2, prop={'size':6})]

def update(dt):
  for i in range(len(x)):
    lab = 'Time:' str(dt dt*i)
    leg[i].set_text(lab)
  return leg

# GIF

graph, = plt.plot([], [], color="gold", markersize=3)
    
plt.close() 

def animate(i):
    graph.set_data(x[:i], y[:i])
    return graph,

skipframes = int(len(x)/500)
if skipframes == 0:
    skipframes = 1

ani = FuncAnimation(fig, update, animate, frames=range(0,len(x),skipframes), interval=20)

CodePudding user response：

To update the labels in your legend you can use:

graph, = plt.plot([], [], color="gold",lw=5,markersize=3,label='Time: 0')
L=plt.legend(loc=1)
L.get_texts()[0].set_text(lab)

L.get_texts()[0].set_text(lab) should be called inside the update function to refresh the label at each iteration of the animation.

You can find a minimal example below to illustrate the process:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

fig,ax = plt.subplots()
dt = 0.01
N_frames=30
x=np.random.choice(100,size=N_frames,) #Create random trajectory
y=np.random.choice(100,size=N_frames,) #Create random trajectory
graph, = plt.plot([], [], color="gold",lw=5,markersize=3,label='Time: 0')
L=plt.legend(loc=1) #Define legend objects

def init():
    ax.set_xlim(0, 100)
    ax.set_ylim(0, 100)
    return graph,

def animate(i):
    lab = 'Time:' str(round(dt dt*i,2))
    graph.set_data(x[:i], y[:i])
    L.get_texts()[0].set_text(lab) #Update label each at frame

    return graph,

ani = animation.FuncAnimation(fig,animate,frames=np.arange(N_frames),init_func=init,interval=200)
plt.show()

And the output gives: