user2241910 user2241910 - 2 months ago 15x
Python Question

matplotlib ConnectionPatch for 3D subplots

Trying to draw a line connecting a point on a 3D subplot to another 3D subplot. In 2D this is easy to do using ConnectionPatch. I've tried to mimic the Arrow3D class from here without luck.

I'm happy for even just a work-around at this point. As an example, in the figure generated by the code below I would want to connect the two green dots.

def cylinder(r, n):
Returns the unit cylinder that corresponds to the curve r.
INPUTS: r - a vector of radii
n - number of coordinates to return for each element in r

OUTPUTS: x,y,z - coordinates of points

# ensure that r is a column vector
r = np.atleast_2d(r)
r_rows, r_cols = r.shape

if r_cols > r_rows:
r = r.T

# find points along x and y axes
points = np.linspace(0, 2*np.pi, n+1)
x = np.cos(points)*r
y = np.sin(points)*r

# find points along z axis
rpoints = np.atleast_2d(np.linspace(0, 1, len(r)))
z = np.ones((1, n+1))*rpoints.T

return x, y, z

# 3D example
fig = plt.figure()

# top figure
ax = fig.add_subplot(2,1,1, projection='3d')
x,y,z = cylinder(np.linspace(2,1,num=10), 40)
for i in range(len(z)):
ax.plot(x[i], y[i], z[i], 'c')
ax.plot([2], [0], [0],'go')

# bottom figure
ax2 = fig.add_subplot(2,1,2, projection='3d')
x,y,z = cylinder(np.linspace(0,1,num=10), 40)
for i in range(len(z)):
ax2.plot(x[i], y[i], z[i], 'r')
ax2.plot([1], [0], [1],'go')


I was trying to solve a very similar problem just tonight! Some of the code may be unnecessary but it will give you the main idea... ...I hope

Inspiration from: and other many and varied sources over the last two hours...

#! /usr/bin/env python

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D
from mpl_toolkits.mplot3d import proj3d
import matplotlib

N = 50
x = np.random.rand(N)
y = np.random.rand(N)
z = np.random.rand(N)

# point's to join
p1 = 10
p2 = 20

fig = plt.figure()

# a background axis to draw lines on
ax0 = plt.axes([0.,0.,1.,1.])

# use these to know how to transform the screen coords
dpi = ax0.figure.get_dpi()
height = ax0.figure.get_figheight() * dpi
width = ax0.figure.get_figwidth() * dpi

# first scatter plot
ax1 = plt.axes([0.05,0.05,0.9,0.425], projection='3d')
ax1.scatter(x, y, z)

# one point of interest
ax1.scatter(x[p1], y[p1], z[p1], s=100.)
x1, y1, _ = proj3d.proj_transform(x[p1], y[p1], z[p1], ax1.get_proj())
[x1,y1] = ax1.transData.transform((x1, y1))  # convert 2d space to screen space
# put them in screen space relative to ax0
x1 = x1/width
y1 = y1/height

# second scatter plot (same data)
ax2 = plt.axes([0.05,0.475,0.9,0.425], projection='3d')
ax2.scatter(x, y, z)

# another point of interest
ax2.scatter(x[p2], y[p2], z[p2], s=100.)
x2, y2, _ = proj3d.proj_transform(x[p2], y[p2], z[p2], ax2.get_proj())
[x2,y2] = ax2.transData.transform((x2, y2))  # convert 2d space to screen space
x2 = x2/width
y2 = y2/height

# set all these guys to invisible (needed?, smartest way?)
for item in [fig, ax1, ax2]:

# draw a line between the transformed points
# again, needed? I know it works...

transFigure = fig.transFigure.inverted()

coord1 = transFigure.transform(ax0.transData.transform([x1,y1]))
coord2 = transFigure.transform(ax0.transData.transform([x2,y2]))

line = matplotlib.lines.Line2D((coord1[0],coord2[0]),(coord1[1],coord2[1]),
fig.lines = line,