CODEWITHSUNDEEP
pythonanimationmatplotlib
HKC72
HKC72

Reputation: 532

How to animate a Polygon (defined by arrays) with Python & Matplotlib

Good day !

Problem explanation: I want to animate a Polygon which values I receive from an array (in my simple example it is a moving sqaure). I want to keep the Polygon's x-and y-values mutable. Dont worry about what movement the Polygon does. It is just an example. Working with "set_xy()" like in the solution from 'animation to translate polygon using matplotlib' is wanted.

Goal -> in every animation frame I want to load the Polygon values from the arrays (P1x,P1y,P2x,P2y,...) and update the figure.

Question: In my code I still have problems to work with the patches. I'm trying to update the Polygon values with the index i. How do I have to define the patch? Does this have to be done bevor the animation call?

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

fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_xlim(-10,10)
ax.set_ylim(-10,10)

P1x=[0.0,0.5,1.0,1.5,2.0,2.5,3.0]
P1y=[0.0,0.0,0.0,0.0,0.0,0.0,0.0]
P2x=[1.0,1.5,2.0,2.5,3.0,3.5,4.0]
P2y=[0.0,0.0,0.0,0.0,0.0,0.0,0.0]
P3x=[1.0,1.5,2.0,2.5,3.0,3.5,4.0]
P3y=[1.0,1.0,1.0,1.0,1.0,1.0,1.0]
P4x=[0.0,0.5,1.0,1.5,2.0,2.5,3.0]
P4y=[1.0,1.0,1.0,1.0,1.0,1.0,1.0]

def init():
    return patch,

def animate(i):
    v = np.array([
                [P1x[i],  P1y[i]],  
                [P2x[i],  P2y[i]],  
                [P3x[i],  P3y[i]],
                [P4x[i],  P4y[i]]
                ])
    patch=patches.Polygon(v,closed=True, fc='r', ec='r')

    return patch,

ani = animation.FuncAnimation(fig, animate, np.arange(1, 5), init_func=init,
                              interval=1000, blit=True)
plt.show()

Thanks a lot for your help!

Upvotes: 0

Views: 727

Answers (1)

ImportanceOfBeingErnest
ImportanceOfBeingErnest

Reputation: 339340

Yes, you will need to create the Polygon first and add it to the axes. Inside the animating function you may use the patch's patch.set_xy() method to update the vertices of the polygon.

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

fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_xlim(-10,10)
ax.set_ylim(-10,10)

P1x=[0.0,0.5,1.0,1.5,2.0,2.5,3.0]
P1y=[0.0,0.0,0.0,0.0,0.0,0.0,0.0]
P2x=[1.0,1.5,2.0,2.5,3.0,3.5,4.0]
P2y=[0.0,0.0,0.0,0.0,0.0,0.0,0.0]
P3x=[1.0,1.5,2.0,2.5,3.0,3.5,4.0]
P3y=[1.0,1.0,1.0,1.0,1.0,1.0,1.0]
P4x=[0.0,0.5,1.0,1.5,2.0,2.5,3.0]
P4y=[1.0,1.0,1.0,1.0,1.0,1.0,1.0]

P = np.concatenate((np.array([P1x, P2x, P3x, P4x]).reshape(4,1,len(P1x)),
                    np.array([P1y, P2y, P3y, P4y]).reshape(4,1,len(P1x))), axis=1)

patch = patches.Polygon(P[:,:,0],closed=True, fc='r', ec='r')
ax.add_patch(patch)

def init():
    return patch,

def animate(i):
    patch.set_xy(P[:,:,i])
    return patch,

ani = animation.FuncAnimation(fig, animate, np.arange(P.shape[2]), init_func=init,
                              interval=1000, blit=True)
plt.show()

Upvotes: 2

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