Re: [Matplotlib-users] plot_surface shading and clipping error

[Benjamin R. <ben...@ou...>]

On Sat, Jul 24, 2010 at 7:18 AM, arsbbr <ar...@gm...> wrote:

>
> Hi,
> i'm trying to make a simple 3d plot of a cylinder with plot_surface.
> There are two problems in my output:
> 1) the shading, shading does not work on the cylindric shell and at the
> same
> time produces weird
> artifacts on the top cover.
> http://old.nabble.com/file/p29254649/cyl-shade-error.png
>
> 2) Sometimes, not reproducible, the inner back of the cylindric shell is
> plotted in front of the top cover. It seems, that it depends somehow on the
> order of the plot commands, so that switching the two plot command helps...
> but not all the time.
> http://old.nabble.com/file/p29254649/cyl-clip-error.png
>
> Am I doing something fundamentally wrong here?
>
> ##########################
> from mpl_toolkits.mplot3d import Axes3D
> import matplotlib.pyplot as plt
> import numpy as np
> from matplotlib import cm
> fig = plt.figure()
> ax = Axes3D(fig)
>
>
> # Cylindrical shell
> phi = np.linspace(0, 2 * np.pi, 100)
> r = np.ones(100)
> h = np.linspace(0, 1, 100)
>
>
> x = 10 * np.outer(np.cos(phi), r)
> y = 10 * np.outer(np.sin(phi), r)
> z = 10 * np.outer(np.ones(np.size(r)), h)
>
>
> # Top cover
> phi_a = np.linspace(0, 2 * np.pi, 100)
> h_2 = np.ones(100)
> r_2 = np.linspace(0, 1, 100)
>
> x_2 = 10 * np.outer(np.cos(phi), r_2)
> y_2 = 10 * np.outer(np.sin(phi), r_2)
> z_2 = 10 * np.ones([100,100])
>
> ax.plot_surface(x, y, z,  rstride=9, cstride=15, linewidth=1, alpha=1)
> ax.plot_surface(x_2, y_2, z_2,  rstride=5, cstride=20, linewidth=1,
> alpha=1)
>
> ax.set_xlabel('X')
> ax.set_ylabel('Y')
> ax.set_zlabel('Z')
>
> plt.show()
> ##########################
>
>
> I'm just a beginner and installed the Enthought Python Distribution 6.2-2,
> which unfortunately
> does not use the matplotlib version 1.0. Since I could not find the .egg
> install file on the matplotlib site I guess I'll have to wait until they
> update EPD.... self compiling is not a real option for me.
>
> Thanks any suggestions!
>
>
arsbbr,

The second problem you mention is a known issue with 3D axes and it is
largely due to issues with overlapping objects and trying to determine which
one gets displayed on top of the other in a 3D -> 2D environment (oh, how I
wish holographic displays were a reality!).  You will find that viewing an
object from certain angles will cause this issue, and then slightly moving
away from those angles will make everything right again.  Unfortunately, I
do not anticipate this issue being solved anytime soon, although it probably
should become a higher priority to me.

I think I have seen the first issue before, but I never fully explored it.
I think I just found my mini-project for the weekend!  I will let you know
what I find.

Ben Root