Line colour of 3D parametric curve in python's matplotlib.pyplot

Question

I've been googling quite some time with no success ... maybe my keywords are just lousy. Anyway, suppose I have three 1D numpy.ndarrays of the same length I'd like to plot them in 3D as a trajectory. Moreover, I'd like to be able to do either of the following things:

1. Change the colour of the line as a function of z
2. Change the colour of the line as a function of time (i.e. the index in the arrays)

This demo has an example of making such a curve:

import matplotlib as mpl from mpl_toolkits.mplot3d import Axes3D import numpy as np import matplotlib.pyplot as plt  fig = plt.figure() ax = fig.gca(projection='3d') theta = np.linspace(-4 * np.pi, 4 * np.pi, 100) z = np.linspace(-2, 2, 100) r = z**2 + 1 x = r * np.sin(theta) y = r * np.cos(theta) ax.plot(x, y, z)  plt.show() 

But how do I achieve 1 or 2? Solutions to only one or the other are welcome! Thanks in advance.

Answer 1

As with normal 2d plots, you cannot have a gradient of color along an ordinary line. However, you can do it with scatter:

import matplotlib as mpl from mpl_toolkits.mplot3d import Axes3D import numpy as np import matplotlib.pyplot as plt  fig = plt.figure() ax = fig.gca(projection='3d') theta = np.linspace(-4 * np.pi, 4 * np.pi, 100) z = np.linspace(-2, 2, 100) r = z**2 + 1 x = r * np.sin(theta) y = r * np.cos(theta)  #1 colored by value of `z` ax.scatter(x, y, z, c = plt.cm.jet(z/max(z)))   #2 colored by index (same in this example since z is a linspace too) N = len(z) ax.scatter(x, y, z, c = plt.cm.jet(np.linspace(0,1,N)))  plt.show() 

---

I liked @Junuxx's hack so I applied it here:

for i in xrange(N-1):     ax.plot(x[i:i+2], y[i:i+2], z[i:i+2], color=plt.cm.jet(255*i/N)) 

Answer 2

You can plot every line segment separately, as shown below. This just loops over 6 predefined colors, since @askewchan's answer already demonstrates well how to use a colormap.

cols = 'rgbcmy'  for i in range(len(x)-1):     ax.plot(x[i:i+2], y[i:i+2], z[i:i+2], color=cols[i%6])