How to set set the marker size of a 3D scatter plot fixed to the axis?

Question

I've asked a similar question before (How to set a fixed/static size of circle marker on a scatter plot?), but now I wanna do it in 3D. How can I do that?

thanks

Answer 1

As in the 2D case, you need to draw the spheres yourself. If you want nicely shaped spheres this means to draw many patches and thus gets slow quite quickly.

Here's a basic way of doing it:

from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
import numpy as np

def plot_shere(ax, x, y, z, r, resolution=100, **kwargs):
    """ simple function to plot a sphere to a 3d axes """

    u = np.linspace(0, 2 * np.pi, resolution)
    v = np.linspace(0, np.pi, resolution)

    xx = r * np.outer(np.cos(u), np.sin(v)) + x
    yy = r * np.outer(np.sin(u), np.sin(v)) + y
    zz = r * np.outer(np.ones(np.size(u)), np.cos(v)) + z

    ax.plot_surface(xx, yy, zz,  rstride=4, cstride=4, **kwargs)

# create some random data (set seed to make it reproducable)
np.random.seed(0)
(x,y,z) = np.random.randint(0,10,(3,5))
r = np.random.randint(2,4,(5,))

# set up the figure
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

# loop through the data and plot the spheres
for p in zip(x,y,z,r):
    plot_shere(ax, *p, edgecolor='none', color=np.random.rand(3))

# set the axes limits and show the plot
ax.set_ylim([-4,14])
ax.set_xlim([-4,14])
ax.set_zlim([-4,14])
plt.show()

Result: