Drawing Circles Of Variable Size And Position On A 2d Animation

I am working with matplotlib in Python 3.3. I have an animated 2d and 3d window, on which I draw points. These points represent objects, but it is not certain that they are actuall

Solution 1:

Drawing Collections is faster, so I modified the draw() function of the PathCollection object returned by scatter(). The new draw() uses transData to calculate the scale of every circle, it uses the size of every circle as diameter.

import pylab as pl
import numpy as np
from matplotlib.collections import Collection
from matplotlib import transforms
import matplotlib.animation as animation

fig = pl.figure()

N = 40
x, y = np.random.rand(2, N)
color = np.random.rand(N)
r = np.random.rand(N) * 0.05 + 0.05

c = pl.scatter(x, y, s=r, c=color, alpha=0.5, animated=True)
pl.gca().set_aspect("equal")

def draw(self, renderer):
    if self._sizes is not None:
        m = self.axes.transData.get_matrix()
        self._transforms = [
            transforms.Affine2D().scale(m[0, 0]*x, m[1, 1]*x)
            for x in self._sizes]
    return Collection.draw(self, renderer)

c.draw = lambda renderer:draw(c, renderer)

def update_loc(n):
    global x2, y2, x, y
    n = n % 50
    if n == 0:
        x2, y2 = np.random.rand(2, N)
    x += (x2 - x) * 0.1
    y += (y2 - y) * 0.1
    c.set_offsets(np.c_[x, y])
    return c,

ani = animation.FuncAnimation(fig, update_loc, 2500, interval=50, blit=True)

pl.show()

Here is a frame of the animation:

Solution 2:

Tcaswell wrote the answer in the comments above, so if you want to upvote this, upvote him too.

The fix was to use a circle: http://matplotlib.org/api/artist_api.html#matplotlib.patches.Circle. These work very different from the axis.plot and axis.scatter in the sens that to add them you have to do the following:

i = pyplot.Circle((item["x"],item["y"]), radius=item["inaccuracy"], fc='None'))
self.ax.add_patch(i)

And to remove them:

i.remove()

tcaswell also suggested that instead of removing every circle before drawing a new set of circles you can also just move and resize i. Which is indeed very possible: just change the radius and xy propertes of i. I have not tested this, but it is not hard to imagine that this will be faster then removing all existing circles and adding all new ones.