Matplotlib contours with overlap control

contour_overlap.py

"""Contours with overlap control.

This script generates widely spaced black contours, with a gray patch in a
subregion where more finely-spaced colored contours are visible.  The gray
patch covers the black contours.
"""

import numpy as np
import matplotlib.mlab as mlab
from matplotlib.patches import Rectangle
import matplotlib.pyplot as plt

def xy(x1, x2, y1, y2, npts):
    x = np.linspace(x1, x2, npts)
    y = np.linspace(y1, y2, npts)
    X, Y = np.meshgrid(x, y)
    return X, Y

def z(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
    return 10.0 * (Z2 - Z1)

# Main script
npts = 250
X, Y = xy(-3,3,-2,2, npts)
Z = z(X, Y)

plt.close('all')

# Create a simple contour plot with labels using default colors.  The
# inline argument to clabel will control whether the labels are draw
# over the line segments of the contour, removing the lines beneath
# the label
plt.figure()
ax = plt.gca()
cs = plt.contour(X, Y, Z, colors='k', linewidths=3, zorder=1)
cs.clabel(inline=1, fontsize=10)
ax = plt.gca()
ax.set_title('Coarse/fine contours with overlap control')

# Rectangular box over subregion.  Left opacity at 0.95 so we can still see the
# covered contours underneath; in practice if full coverage is desired, simply
# omit the alpha parameter
rect = Rectangle((0,0), 2, 1.5, facecolor="#aaaaaa", alpha=0.95, zorder=5)
ax.add_patch(rect)

# Second patch of more finely spaced contours in a subregion (over box)
Xs, Ys = xy(0, 2, 0, 1.5, npts)
Zs = z(Xs, Ys)
cs2 = ax.contour(Xs, Ys, Zs, 15, zorder=10)

plt.show()