How to change the line formate in animation? [duplicate] - python-3.x

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Animate points with labels with matplotlib
(3 answers)
Closed 5 years ago.
I made this animation using matplotlib and it is working properly, however, i need to add some animated labels to be moving with its corresponding points.
The first label to be referring to the intersection point between the circle and the horizontal line from the centre of the ellipse and the other text label is to be in the middle of the inclined line annotating its length.
I tried some ideas but nothing worked properly. Any ideas?
screenshot
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
fig = plt.figure()
ax = fig.add_subplot(111, autoscale_on=True, xlim=(-6, 6), ylim=(-7, 17))
# ax.grid()
line, = ax.plot([], [], 'k', lw=1)
line2, = ax.plot([], [], 'k--', lw=1)
a,b = 3,2
x,y = list(),list()
x1 =np.array([item/10 for item in range(-30,31)])
y1 = np.sqrt(b**2 * (1-(x1**2 / a**2)))
x =list(x1)+[-item for item in list(x1)]
y =list(y1)+[-item for item in list(y1)]
plt.plot(x, y, 'k:')
plt.plot((0,0), (0,15), 'k--')
ax.annotate('$A$', xy=(0,15), xytext=(-10, 10),color='b',
textcoords='offset points')
ax.annotate('$O$', xy=(0,-1), xytext=(-10, 10),color='b',ha='center',
textcoords='offset points')
ax.annotate('$4a$', xy=(0,7), xytext=(-10, 10),color='b',ha='center',
textcoords='offset points', family='sans serif')
def animate(i):
thisx = [0, x[i]]
thisy = [15, y[i]]
xx = [x[i], 0]
yy = [y[i], 0]
line.set_data(thisx, thisy)
line2.set_data(xx, yy)
return line, line2
ani = animation.FuncAnimation(fig, animate, np.arange(0, len(x)), interval=20, blit=False)
ax.annotate('$P$', xy=(3,0), xytext=(0, 0),color='b',ha='center',
textcoords='offset points', family='sans serif', style='italic')
plt.show()
# ani.save('circular_motion.mp4', fps=20)
#
plt.close()

Answer 1

You can alter the annotation properties in the same way that you alter the line properties. Just store the Annotation object that is returned from the ax.annotation command and then update its position in the animate function. Note that the function set_position does not work properly, as was also noted in here, therefore you have to use the xy attribute.
Furthermore, I noticed that your animation runs faster when you y values are close to zero. You can fix that (if it needs fixing) by defining a vector of angles and computing the xy coordinates from that. I took the freedom to alter your code to show what I mean.
About the length of the inclined line, I annotated it here as L, as you don't state what the length of the distance OP is, but I guess that you can fill that in yourself.
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
fig = plt.figure()
ax = fig.add_subplot(111, autoscale_on=True, xlim=(-6, 6), ylim=(-7, 17))
# ax.grid()
line, = ax.plot([], [], 'k', lw=1)
line2, = ax.plot([], [], 'k--', lw=1)
a,b = 3,2
x,y = list(),list()
z = 15
phi = np.linspace(0,2*np.pi,100)
x = a * np.cos(phi)
y = -b * np.sin(phi)
plt.plot(x, y, 'k:')
plt.plot((0,0), (0,z), 'k--')
ax.annotate('$A$', xy=(0,15), xytext=(-10, 10),color='b',
textcoords='offset points')
ax.annotate('$O$', xy=(0,-1), xytext=(-10, 10),color='b',ha='center',
textcoords='offset points')
ax.annotate('$4a$', xy=(0,7), xytext=(-10, 10),color='b',ha='center',
textcoords='offset points', family='sans serif')
def animate(i):
thisx = [0, x[i]]
thisy = [z, y[i]]
xx = [x[i], 0]
yy = [y[i], 0]
line.set_data(thisx, thisy)
line2.set_data(xx, yy)
P.xy = (x[i]*1.05,y[i])
L.xy = ((x[i]/2)*1.05, z/2+y[i]/2)
return line, line2, P, L
ani = animation.FuncAnimation(fig, animate, np.arange(0, len(x)), interval=20, blit=False)
P = ax.annotate('$P$', xy=(a,0), xytext=(0, 0),color='b',ha='center',
textcoords='offset points', family='sans serif', style='italic')
L = ax.annotate('$L$', xy=(a/2,z/2), xytext=(0, 0),color='b',ha='center',
textcoords='offset points', family='sans serif', style='italic')
plt.show()
# ani.save('circular_motion.mp4', fps=20)
#
plt.close()
Hope this helps.