First of all, I am just starting to learn Python. I have been struggling during the last hours trying to update the arrow properties in order to change them during a plot animation.
After thoroughly looking for an answer, I have checked that it is possible to change a circle patch center by modifying the attribute 'center' such as circle.center = new_coordinates. However, I don't find the way to extrapolate this mechanism to an arrow patch...
The code so far is:
import numpy as np, math, matplotlib.patches as patches
from matplotlib import pyplot as plt
from matplotlib import animation
# Create figure
fig = plt.figure()
ax = fig.gca()
# Axes labels and title are established
ax = fig.gca()
ax.set_xlabel('x')
ax.set_ylabel('y')
ax.set_ylim(-2,2)
ax.set_xlim(-2,2)
plt.gca().set_aspect('equal', adjustable='box')
x = np.linspace(-1,1,20)
y = np.linspace(-1,1,20)
dx = np.zeros(len(x))
dy = np.zeros(len(y))
for i in range(len(x)):
dx[i] = math.sin(x[i])
dy[i] = math.cos(y[i])
patch = patches.Arrow(x[0], y[0], dx[0], dy[0] )
def init():
ax.add_patch(patch)
return patch,
def animate(t):
patch.update(x[t], y[t], dx[t], dy[t]) # ERROR
return patch,
anim = animation.FuncAnimation(fig, animate,
init_func=init,
interval=20,
blit=False)
plt.show()
After trying several options, I thought that the function update could somehow take me closer to the solution. However, I get the error:
TypeError: update() takes 2 positional arguments but 5 were given
If I just add one more patch per step by defining the animate function as shown below, I get the result shown in the image attached.
def animate(t):
patch = plt.Arrow(x[t], y[t], dx[t], dy[t] )
ax.add_patch(patch)
return patch,
Wrong animation
I have tried to add a patch.delete statement and create a new patch as update mechanism but that results in an empty animation...
Add ax.clear() before ax.add_patch(patch) but will remove all elements from plot.
def animate(t):
ax.clear()
patch = plt.Arrow(x[t], y[t], dx[t], dy[t] )
ax.add_patch(patch)
return patch,
EDIT: removing one patch
using ax.patches.pop(index).
In your example is only one patch so you can use index=0
def animate(t):
ax.patches.pop(0)
patch = plt.Arrow(x[t], y[t], dx[t], dy[t] )
ax.add_patch(patch)
return patch,
using ax.patches.remove(object)
It needs global to get/set external patch with Arrow
def animate(t):
global patch
ax.patches.remove(patch)
patch = plt.Arrow(x[t], y[t], dx[t], dy[t] )
ax.add_patch(patch)
return patch,
BTW: to get list of properties which you can use with update()
print( patch.properties().keys() )
dict_keys(['aa', 'clip_path', 'patch_transform', 'edgecolor', 'path', 'verts', 'rasterized', 'linestyle', 'transform', 'picker', 'capstyle', 'children', 'antialiased', 'sketch_params', 'contains', 'snap', 'extents', 'figure', 'gid', 'zorder', 'transformed_clip_path_and_affine', 'clip_on', 'data_transform', 'alpha', 'hatch', 'axes', 'lw', 'path_effects', 'visible', 'label', 'ls', 'linewidth', 'agg_filter', 'ec', 'facecolor', 'fc', 'window_extent', 'animated', 'url', 'clip_box', 'joinstyle', 'fill'])
so you can use update to change color - `facecolor
def animate(t):
global patch
t %= 20 # get only 0-19 to loop animation and get color t/20 as 0.0-1.0
ax.patches.remove(patch)
patch = patches.Arrow(x[t], y[t], dx[t], dy[t])
patch.update({'facecolor': (t/20,t/20,t/20,1.0)})
ax.add_patch(patch)
return patch,
I found this by mimicking the code in patches.Arrow.__init__:
import numpy as np
import matplotlib.patches as patches
from matplotlib import pyplot as plt
from matplotlib import animation
import matplotlib.transforms as mtransforms
# Create figure
fig, ax = plt.subplots()
# Axes labels and title are established
ax.set_xlabel('x')
ax.set_ylabel('y')
ax.set_ylim(-2,2)
ax.set_xlim(-2,2)
ax.set_aspect('equal', adjustable='box')
N = 20
x = np.linspace(-1,1,N)
y = np.linspace(-1,1,N)
dx = np.sin(x)
dy = np.cos(y)
patch = patches.Arrow(x[0], y[0], dx[0], dy[0])
def init():
ax.add_patch(patch)
return patch,
def animate(t):
L = np.hypot(dx[t], dy[t])
if L != 0:
cx = float(dx[t]) / L
sx = float(dy[t]) / L
else:
# Account for division by zero
cx, sx = 0, 1
trans1 = mtransforms.Affine2D().scale(L, 1)
trans2 = mtransforms.Affine2D.from_values(cx, sx, -sx, cx, 0.0, 0.0)
trans3 = mtransforms.Affine2D().translate(x[t], y[t])
trans = trans1 + trans2 + trans3
patch._patch_transform = trans.frozen()
return patch,
anim = animation.FuncAnimation(fig, animate,
init_func=init,
interval=20,
frames=N,
blit=False)
plt.show()
