How to annotate/highlight a 3d plot in MatPlotLib

Question

I would like to do something like this: http://matplotlib.sourceforge.net/_images/86cbd17f31.png in a 3d space. Basically I want to highlight a portion of a surface plot. Any suggestions?

Answer 1

edit3 (this replaces a very mis-guided previous answer)

updated again. See comment

You can modify the face colors of a surface plot if you drill down to the polygon collection that is generated by the plot. It does some magic shading and re-orders the list of colors depending on zorder so I had some trouble figuring out how to keep the assigned shading in the un-highlighted region yet still be able to index the region of interests. Here is a method that works. I hope you wanted shaded faces and not some kind of 3D semi-transparent columns. This could also be done, but I think it would be very difficult to tell what is highlighted and would be really tricky to define the zorder.

import matplotlib.pyplot as plt
from matplotlib import cm
from mpl_toolkits.mplot3d import Axes3D
import numpy as np
import mpl_toolkits.mplot3d.art3d as art3d
from matplotlib.patches import Rectangle, PathPatch

fig = plt.figure()
ax = fig.gca(projection='3d')
X = np.arange(-5, 5, 0.25)
Y = np.arange(-5, 5, 0.25)
X, Y = np.meshgrid(X, Y)
R = np.sqrt(X**2 + Y**2)
Z = np.sin(R)

xlo = X.min()
xhi = X.max()
ylo = Y.min()
yhi = Y.max()
zlo = -2
zhi = 2

surf = ax.plot_surface(X, Y, Z, rstride=1, cstride=1, linewidth=1, zorder=100)
cset = ax.contour(X, Y, Z, zdir='z', offset=zlo, alpha=0.0)

def highlight((xmin, xmax),(ymin, ymax)):
    # draw highlight on xz plane
    p1 = Rectangle((ymin,zlo),(ymax-ymin),(zhi-zlo), color='y', alpha=0.5, zorder=0)
    ax.add_patch(p1)
    art3d.pathpatch_2d_to_3d(p1, z=xlo, zdir='x')

    # draw highlight on yz plane
    p2 = Rectangle((xmin,zlo),(xmax-xmin),(zhi-zlo), color='y', alpha=0.5, zorder=0)
    ax.add_patch(p2)
    art3d.pathpatch_2d_to_3d(p2, z=yhi, zdir='y')

    # define a region to highlight
    highlight = (X>xmin)&(X<xmax)&(Y>ymin)&(Y<ymax)
    coll = ax.collections[0]
    # get the original color shading (if you want to keep that effect)
    colors = coll._facecolors_original
    #colors = coll.get_facecolors()
    # they are stored as a list for some reason so get the flat indicies
    for idx in np.where(highlight[:-1,:-1].flat)[0]:
        # and modifly one-by-one
        color = colors[idx][:]
        colors[idx][0] = color[2]  # swap red with blue
        colors[idx][3] = color[0]
        colors[idx][4] = .2  #change alpha
    # re-set the face colors
    coll.set_facecolors(colors)

highlight((-3,0),(-3,1))

ax.set_xlim3d(xlo, xhi)
ax.set_ylim3d(ylo, yhi)
ax.set_zlim3d(zlo, zhi)

plt.show()