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

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

On Sat, Jul 24, 2010 at 2:46 PM, arsbbr <ar...@gm...> wrote:

>
> Thank you for looking into it!
> It would be perfectly fine for me to merge the two objects, so that one
> surface_plot command will do it.
> Maybe someone can give me a hint how to accomplish that?
>
> I appreciate any tips.
>
>
>
> Benjamin Root-2 wrote:
> >
> > 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.
> >
>

Actually, looks like your problem was relatively simple.  The construction
of the top surface wasn't done quite right and the striding was causing
blocks to be skipped.  Try this:

phi_grid, r_grid = np.meshgrid(phi_a, r_2)
x_2 = 10 * np.cos(phi_grid) * r_grid
y_2 = 10 * np.sin(phi_grid) * r_grid
z_2 = 10 * np.ones([100,100])

The thing to keep in mind when creating a surface in 3d is that the data
needs to be considered as parameterizable in 2D and constructed as such.

I hope that helps,

Ben Root