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When trying to enforce rasterization of a Poly3DCollection object in Matplotlib, I get the following error message (and I can confirm no rasterization is applied):

/usr/lib/python3/dist-packages/matplotlib/artist.py:788: UserWarning: Rasterization of '<mpl_toolkits.mplot3d.art3d.Poly3DCollection object at 0x2b49e8faeba8>' will be ignored
  warnings.warn("Rasterization of '%s' will be ignored" % self)

It is possible to rasterize the entire figure, but it is obviously preferable to only rasterize some objects, while keeping items like axes, labels, key, text, etc. as vector graphics.

I have tried using the following syntax in my code:

  • ax.add_collection3d(Poly3DCollection(polygons, rasterized=True), zs='z')
  • c = Poly3DCollection(polygons) and then c.set_rasterized(True)

According to this post, it is possible to rasterize a PolyCollection (without the 3D bit) object.

Any suggestions?

Here is an MWE:

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

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

ax.set_xlim([0, 4])
ax.set_ylim([0, 4])
ax.set_zlim([0, 4])

polygons = [[(3, 1, 1), (1, 3, 1), (1, 1, 3)]]

ax.add_collection3d(Poly3DCollection(polygons, facecolors='r', rasterized=True), zs='z')

plt.show()
PhilippVerpoort
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  • I don't know for sure but suspect that this is impossible by design. How would you handle, for example, a rotation of the viewing angle that is not a multiple of 90 degrees, if the 3d object being viewed has been rasterized (into cubes?)? – Paul Brodersen Dec 14 '17 at 18:29
  • @Paul Rasterization is only meant for export. There is nothing rasterized on screen so you can still rotate your plot as usual. – ImportanceOfBeingErnest Dec 14 '17 at 20:06
  • Oh, I assumed that it would be handled as e.g. in gimp, where when you rasterize an object, it is actually converted to a bitmap, AFAIK. Thanks for the clarification, @ImportanceOfBeingErnest – Paul Brodersen Dec 15 '17 at 15:44
  • @Paul You are completely right. The point is, rasterization in matplotlib will only affect the exported file. In the exported pdf you'll see the shape is bitmap-like (see screenshot in my answer below). Since you cannot rotate the plot once it is in pdf format, this is all perfectly fine. – ImportanceOfBeingErnest Dec 15 '17 at 16:05

1 Answers1

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First note that rasterization is only useful for exporting in a vector graphics, like pdf. I am assuming that this is what you are talking about here, so I suppose you would call something like plt.savefig("some.pdf") at the end.

I think someone just forgot to allow rasterizations for 3D objects.

A fix would be to go into the matplotlib source code, locate 

python\lib\site-packages\mpl_toolkits\mplot3d\art3d.py

In the imports section add 

from matplotlib.artist import allow_rasterization

and further down inside Poly3DCollection find its draw method (In my case it's at line 709) and add @allow_rasterization. It should then look like

@allow_rasterization
def draw(self, renderer):
    return Collection.draw(self, renderer)

If then running the above code, plus saving it to pdf, the triangle is rasterized. Screenshot of pdf:

enter image description here

ImportanceOfBeingErnest
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