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I'm attempting to plot 3D line trajectories that evolve over time, and I would like the colors to change to show that passage of time (e.g. from light blue to dark blue). However, there is a distinct lack of tutorials for using matplotlib's Line3DCollection; this is the closest I could find, but all I'm getting is a white line.

Here's my code.

import matplotlib.pyplot as plot
from mpl_toolkits.mplot3d.axes3d import Axes3D
from mpl_toolkits.mplot3d.art3d import Line3DCollection
import numpy as np

# X has shape (3, n)
c = np.linspace(0, 1., num = X.shape[1])[::-1]
a = np.ones(shape = c.shape[0])
r = zip(a, c, c, a) # an attempt to make red vary from light to dark

# r, which contains n tuples of the form (r,g,b,a), looks something like this:
# [(1.0, 1.0, 1.0, 1.0), 
# (1.0, 0.99998283232330165, 0.99998283232330165, 1.0),
# (1.0, 0.9999656646466033, 0.9999656646466033, 1.0),
# (1.0, 0.99994849696990495, 0.99994849696990495, 1.0),
# ..., 
# (1.0, 1.7167676698312416e-05, 1.7167676698312416e-05, 1.0),
# (1.0, 0.0, 0.0, 1.0)]

fig = plot.figure()
ax = fig.gca(projection = '3d')

points = np.array([X[0], X[1], X[2]]).T.reshape(-1, 1, 3)
segs = np.concatenate([points[:-1], points[1:]], axis = 1)
lc = Line3DCollection(segs, colors = r)
ax.add_collection3d(lc)

ax.set_xlim(-0.45, 0.45)
ax.set_ylim(-0.4, 0.5)
ax.set_zlim(-0.45, 0.45)

plot.show()

However, here's what I get:

3d temporal color change plot

Just a bunch of white line segments, no shift in the color. What am I doing wrong? Thanks!

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Magsol
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2 Answers2

6

Your code works just fine, here's a bit of a sample. Basically, this is your code with a custom X set.

fig = plot.figure();
ax = fig.gca(projection = '3d')
X = [(0,0,0,1,0),(0,0,1,0,0),(0,1,0,0,0)]
points = np.array([X[0], X[1], X[2]]).T.reshape(-1, 1, 3)
r = [(1.0, 1.0, 1.0, 1.0), (1.0, 0.75, 0.75, 1.0), (1.0, 0.5, 0.5, 1.0), (1.0, 0.25, 0.25, 1.0), (1.0, 0.0, 0.0, 1.0)];

segs = np.concatenate([points[:-1], points[1:]], axis = 1)
ax.add_collection(Line3DCollection(segs,colors=list(r)))

plot.show()

And the plot looks like this:

enter image description here

PearsonArtPhoto
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  • Additional Matplotlib examples are *always* welcome :) Thank you again! – Magsol Feb 27 '14 at 22:09
  • This seems to be what I am searching for. just that I am not sure if your example works for the case that I read the points from Excel rows and I want the segments order be the same as the reading order. should anything change ? – FabioSpaghetti Jun 24 '19 at 07:31
1

Wow, so it turns out the problem was that X was actually not of shape (3, n), but rather something like (3, n^10), but I was only plotting n points, hence the color appeared to never change (and why r seems to have extremely small intervals...there were something like 58,000 points when I was plotting only 250).

So yes, it was a bug. Sorry about that; it works fine now.

Magsol
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  • With no disrespect intended, I'm voting to close this question as it's unlikely to help other readers. – Hooked Feb 27 '14 at 20:35
  • @Hooked: It is a valid code sample of how to do this, and there isn't really anything on the web that I can find. It might be useful, I'd be inclined to keep it around... – PearsonArtPhoto Feb 27 '14 at 20:37
  • @PearsonArtPhoto The question lacked value to future readers until you posted your example, which was at the same time as my comment. I'll retract the close vote. – Hooked Feb 27 '14 at 20:40