Can someone tell me what's wrong with my animation code?

Question

Can someone tell me what's wrong with my animation code?

I coded this program that will generate 40 png images, and an animated gif image.

The animation is supposed to be a sphere that is sliced into 5 segments, and the segments move left and right, but, as you will be able to see, it doesn't really work as I planned

(I only posted 12 frames of the gif, as 40 frames will be to big to post)

Can someone tell me how to correct it?

import matplotlib.pyplot as plt
from numpy import sin,cos,pi,outer,ones,size,linspace
from mpl_toolkits.mplot3d import axes3d

# Define the x, y, and z lists for the sphere:
x = 10*outer(cos(linspace(0, 2*pi)), sin(linspace(0, pi)))
y = 10*outer(sin(linspace(0, 2*pi)), sin(linspace(0, pi)))
z = 10*outer(ones(size(linspace(0, 2*pi))), cos(linspace(0, pi)))

for n in range(40):
    fig = plt.figure(figsize=(10, 10))
    ax = fig.add_subplot(111, projection='3d')
    ax.plot_surface(x, y, z, color = ('r'))
    ax.set_xticks([])
    ax.set_yticks([])
    ax.set_zticks([])
    ax.set_xlim(-10,10)
    ax.set_ylim(-10,10)
    ax.set_zlim(-10,10)
    plt.savefig(str(n)+'.png') #Save the image into a numbered png file
    print(str(n)+'.png completed.')
    plt.close()

    sign = 1
    for count in range(5): #Slice the sphere into 5 segments
        for num in range(len(z)//5*count,len(z)//5*(count+1)):
            z[num] += sign # Make the segments go positive and negative directions
            sign *= -1

from PIL import Image
images = []
# Open each png file and store in images list
for n in range(40):
    exec('a'+str(n)+'=Image.open("'+str(n)+'.png")')
    images.append(eval('a'+str(n)))
# Create an animated gif file:
images[0].save('ball.gif',
               save_all=True,
               append_images=images[1:],
               duration=100,
               loop=0)

Answer 1

The problem is that you are using the same array for all segments, so the plot will stay connected at some vertices. That just how the plotting function works, it does not know that you want to separate the parts.

You have to split the array before, then modify the parts separately.

At best this is done for x and y also, then you don't have to fiddle with the indices and that annoying inner for-loop:)

I prepared something for you to start with:

import matplotlib.pyplot as plt
from numpy import sin,cos,pi,outer,ones,size,linspace
from mpl_toolkits.mplot3d import axes3d
import numpy as np

# Define the x, y, and z lists for the sphere:
x = 10*outer(cos(linspace(0, 2*pi)), sin(linspace(0, pi)))
y = 10*outer(sin(linspace(0, 2*pi)), sin(linspace(0, pi)))

z = 10*outer(ones(size(linspace(0, 2*pi))), cos(linspace(0, pi)))

def split_and_array(a):
    return np.array(np.split(a, 5, axis=0))

x = split_and_array(x)
y = split_and_array(y)
z = split_and_array(z)

for n in range(40):
    fig = plt.figure(figsize=(10, 10))
    ax = fig.add_subplot(111, projection='3d')

    for k in range(5):
        ax.plot_surface(x[k], y[k], z[k], color = ('r'))

    ax.set_xticks([])
    ax.set_yticks([])
    ax.set_zticks([])
    ax.set_xlim(-10,10)
    ax.set_ylim(-10,10)
    ax.set_zlim(-10,10)
    plt.savefig(str(n)+'.png') #Save the image into a numbered png file
    print(str(n)+'.png completed.')
    plt.close()

    sign = 1
    for count in range(5): #Slice the sphere into 5 segments

        z[count] += sign # Make the segments go positive and negative directions
        sign *= -1