Real-time plotting of a custom turning marker - matplotlib

Question

Is it somehow possible to plot a custom marker (like this) interactively, but have it turn in real-time? It seems that the scatter graph does not grant any access to the markers.

Answer 1

You can create a custom marker with a FancyArrowPatch. Many styles and options are possible. Such a patch is not easy to update, but you could just remove the patch and create it again to create an animation.
The easiest way to create an animation is via plt.pause(), but that doesn't work in all environments. Another way is via FuncAnimation, which involves a few more lines, but makes controlling the animation easier.
Here is some example code to show the concepts:
import matplotlib.pyplot as plt
from matplotlib import patches
from matplotlib.collections import PatchCollection
from matplotlib import animation
import numpy as np
fig, ax = plt.subplots()
N = 50
x = np.random.uniform(-20, 20, (N, 2))
dx = np.random.uniform(-1, 1, (N, 2))
dx /= np.linalg.norm(dx, axis=1, keepdims=True)
colors = plt.cm.magma(np.random.uniform(0, 1, N))
arrow_style = "Simple,head_length=2,head_width=3,tail_width=1"
ax.set_xlim(-40, 40)
ax.set_ylim(-30, 30)
ax.set_aspect('equal')
old_arrows = None
def animate(i):
global old_arrows, x, dx
if old_arrows is not None:
old_arrows.remove()
x += dx
dx += np.random.uniform(-.1, .1, (N, 2))
dx /= np.linalg.norm(dx, axis=1, keepdims=True)
arrows = [patches.FancyArrowPatch((xi, yi), (xi + dxi * 10, yi + dyi * 10), arrowstyle=arrow_style)
for (xi, yi), (dxi, dyi) in zip(x, dx)]
old_arrows = ax.add_collection(PatchCollection(arrows, facecolors=colors))
return old_arrows,
ani = animation.FuncAnimation(fig, animate, np.arange(1, 200),
interval=25, repeat=False, blit=True)
plt.show()

Answer 2

I solved it by remove() and static variables like this:
class pltMarker:
def __init__(self, angle=None, pathString=None):
self.angle = angle or []
self.pathString = pathString or """simply make and svg, open in a text editor and copy the path XML string in here"""
self.path = parse_path( self.pathString )
self.path.vertices -= self.path.vertices.mean( axis=0 )
self.marker = mpl.markers.MarkerStyle( marker=self.path )
self.marker._transform = self.marker.get_transform().rotate_deg(angle)
def rotate(self, angle=0):
self.marker._transform = self.marker.get_transform().rotate_deg(angle)
def animate(k):
angle = ... # new angle
myPltMarker.rotate(angle)
animate.Scatter.remove()
animate.Scatter = plt.scatter(1, 0, marker=myPltMarker.marker, s=100)
return animate.Scatter,
angle = ...
myPltMarker = pltMarker(angle=angle)
animatePlt.Scatter = plt.scatter(1, 0, marker=myPltMarker.marker, s=100)
anm = animation.FuncAnimation(fig, animate, blit=False, interval=1)
plt.show()