Transparency for Poly3DCollection plot in matplotl

问题:

I am trying to draw some objects with the fabulous Matplotlib package for Python. These objects consist of points implemented with plt.scatter() and patches implemented with Poly3DCollection. I would like to have the patches with a slight transparency so that the points and edges behind the patches can be seen.

Here the code and plot I already generated. Seems I am almost there, just missing the feature of transparency. Interestingly, if I first plot the Ploy3DCollection and afterwards the scatter points, the points can be seen, but not the edges.

Anyone having a suggestion for me?

from matplotlib import pyplot as plt
from mpl_toolkits.mplot3d.art3d import Poly3DCollection

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

x = [0, 2, 1, 1]
y = [0, 0, 1, 0]
z = [0, 0, 0, 1]

vertices = [[0, 1, 2], [0, 1, 3], [0, 2, 3], [1, 2, 3]]

tupleList = zip(x, y, z)

poly3d = [[tupleList[vertices[ix][iy]] for iy in range(len(vertices[0]))] for ix in range(len(vertices))]
ax.scatter(x,y,z)
ax.add_collection3d(Poly3DCollection(poly3d, facecolors='w', linewidths=1, alpha=0.5))

plt.show()

回答1:

I made a slight modification to the OP code and got the transparency working. It appears that the facecolors argument of Poly3DCollection overrides the transparency argument, so the solution was to set the color in a separate call to either Poly3DCollection.set_color or Poly3DCollection.set_facecolor:

from matplotlib import pyplot as plt
from mpl_toolkits.mplot3d.art3d import Poly3DCollection

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

x = [0, 2, 1, 1]
y = [0, 0, 1, 0]
z = [0, 0, 0, 1]

vertices = [[0, 1, 2], [0, 1, 3], [0, 2, 3], [1, 2, 3]]

tupleList = zip(x, y, z)

poly3d = [[tupleList[vertices[ix][iy]] for iy in range(len(vertices[0]))] for ix in range(len(vertices))]
ax.scatter(x,y,z)
collection = Poly3DCollection(poly3d, linewidths=1, alpha=0.2)
face_color = [0.5, 0.5, 1] # alternative: matplotlib.colors.rgb2hex([0.5, 0.5, 1])
collection.set_facecolor(face_color)
ax.add_collection3d(collection)

plt.show()

Interestingly, if you explicitly set the edge color with collection.set_edgecolor('k'), the edges will also honor the transparency setting.

回答2:

I found a nice workaround: After plotting the data, do another plot on top with the same color and lighter line style. Instead of Poly3DCollection I use Line3DCollection, so no faces are plotted. The result looks very much as anticipated.

See below the new plot and the script creating it.

from matplotlib import pyplot as plt
from mpl_toolkits.mplot3d.art3d import Poly3DCollection, Line3DCollection

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

x = [0, 2, 1, 1]
y = [0, 0, 1, 0]
z = [0, 0, 0, 1]

vertices = [[0, 1, 2], [0, 1, 3], [0, 2, 3], [1, 2, 3]]

tupleList = zip(x, y, z)

poly3d = [[tupleList[vertices[ix][iy]] for iy in range(len(vertices[0]))] for ix in range(len(vertices))]
ax.scatter(x,y,z)
ax.add_collection3d(Poly3DCollection(poly3d, facecolors='w', linewidths=1, alpha=0.5))
ax.add_collection3d(Line3DCollection(poly3d, colors='k', linewidths=0.2, linestyles=':'))

plt.show()

回答3:

Thanks a lot Chilichiller and Julian. Your examples are very useful to me at present, because I am working on a little project about 3D representation of matrices with matplotlib, and Poly3DCollection seems suitable for the task.

A little note, that maybe can be useful to future readers. Running your examples in Python 3 gives TypeError: 'zip' object is not subscriptable.

The simplest solution is to wrap the return value of zip in a call to list() (as indicated by "Dive Into Python 3": http://www.diveintopython3.net/porting-code-to-python-3-with-2to3.html).

回答4:

This bug has been fixed in the new matplotlib. I'm running version 1.5.1.

You can see your version by running python, then doing:

import matplotlib
matplotlib.__version__

You can get matplotlib using pip. If you're on Ubuntu, run this from a terminal:

sudo apt-get install python-pip
sudo pip install matplotlib