How to do Cartopy simple animations - python-3.x

Question

I am trying to create a simple animation using Cartopy. Basically just drawing a few lines in the map. So far I am trying the following:
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import matplotlib.animation as animation
import numpy as np
ax = plt.axes(projection=ccrs.Robinson())
ax.set_global()
ax.coastlines()
lons = 10 * np.arange(1, 10)
lats = 10 * np.arange(1, 10)
def animate(i):
plt.plot([lons[i-1], lons[i]], [lats[i-1], lats[i]], color='blue', transform=ccrs.PlateCarree())
return plt
anim = animation.FuncAnimation(plt.gcf(), animate, frames=np.arange(1, 8), init_func=None, interval=2000, blit=True)
plt.show()
Does anyone know why this is not working?

Answer 1

This is unrelated to cartopy, I would guess. The problem is that you cannot return pyplot from the animation function. (It's like instead of buying a book, you'd buy the whole book store and then wonder why you can't read a book store.)
The easiest solution is to turn blitting off:
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import numpy as np
fig, ax = plt.subplots()
lons = 10 * np.arange(1, 10)
lats = 10 * np.arange(1, 10)
def animate(i):
plt.plot([lons[i-1], lons[i]], [lats[i-1], lats[i]], color='blue')
anim = animation.FuncAnimation(plt.gcf(), animate, frames=np.arange(1, 8),
init_func=None, interval=200, blit=False)
plt.show()
If for some reason you need blitting (which would the case if the animation is too slow or consumes too much CPU), you need to return a list of the Line2D objects you want to draw.
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import numpy as np
fig, ax = plt.subplots()
lons = 10 * np.arange(1, 10)
lats = 10 * np.arange(1, 10)
lines = []
def animate(i):
line, = plt.plot([lons[i-1], lons[i]], [lats[i-1], lats[i]])
lines.append(line)
return lines
anim = animation.FuncAnimation(plt.gcf(), animate, frames=np.arange(1, 8),
interval=200, blit=True, repeat=False)
plt.xlim(0,100) #<- remove when using cartopy
plt.ylim(0,100)
plt.show()

Answer 2

The Warining is
The animation function must return a sequence of Artist objects
So just change the blit keyword from True to false and then save the animation into a gif file can solve this.
Otherwise, you can plot a sequence of Artist objects can then set the
blit=True as follows:
ax = plt.axes(projection=ccrs.Robinson())
ax.set_global()
ax.coastlines()
lons = 10 * np.arange(1, 10)
lats = 10 * np.arange(1, 10)
def animate(i):
line = ax.plot([lons[i-1], lons[i]], [lats[i-1], lats[i]], color='blue', transform=ccrs.PlateCarree())
return line
anim = animation.FuncAnimation(plt.gcf(), animate, frames=np.arange(1, 8), init_func=None, interval=200, blit=True)
anim.save('test.gif')
plt.show()
May these help you.