How to overlay a controuf plot with a differently colored contour plot?

Question

(I've asked the same in MATLAB before)

I'd like to overlay for example a seismic-cmapped contourf-plot (or pcolor) with a grayscale contour-plot, but when I add the latter it also changes the previous colormap. How can this be fixed?

Answer 1

This answer is taken almost entirely from the contour demo example:

import numpy as np
import matplotlib.cm as cm
import matplotlib.mlab as mlab # for setting up the data
import matplotlib.pyplot as plt

# set up example data:
delta = 0.025
x = np.arange(-3.0, 3.0, delta)
y = np.arange(-2.0, 2.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = mlab.bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = mlab.bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
# difference of Gaussians
Z = 10.0 * (Z2 - Z1)

levels = 10

# plot the filled contour
# using a colormap (jet)
CF = plt.contourf(Z, levels,
                  extent=(-3,3,-2,2),cmap=cm.jet)

# plot the contour lines
# using gray scale
CL = plt.contour(Z, levels,
                 linewidths=2,
                 extent=(-3,3,-2,2),cmap=cm.gray)

# plot color bars for both contours (filled and lines)
CB = plt.colorbar(CL, extend='both')
CBI = plt.colorbar(CF, orientation='horizontal')

# Plotting the second colorbar makes 
# the original colorbar look a bit out of place,
# so let's improve its position.

l,b,w,h = plt.gca().get_position().bounds
ll,bb,ww,hh = CB.ax.get_position().bounds
CB.ax.set_position([ll, b, ww, h])

plt.show()

And you'll end up with this plot: