Problem viewing mplot3d figure

Community matplotlib-users
1

Hello all.

I'm attempting to use bar3d to plot a packing solution but from some
viewpoints the perspective is wrong (boxes seem overlapped), and with a
large number of boxes the plot is always incoherent.

(I'm using matplotlib 1.0.0 on fedora 14)

Does anyone know how to fix this?

Cheers,
Miguel

Example code:

···

-----------------------------------------------------------------------

import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

# setup figure
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.set_xlim3d(0, 10)
ax.set_ylim3d(0, 10)
ax.set_zlim3d(0, 10)

# boxes
x = [0,2,0,2,0]
y = [0,0,2,2,0]
z = [0,0,0,0,2]
dx = [2,2,2,2,3]
dy = [2,2,2,2,3]
dz = [2,2,2,2,3]
colors = ['b','b','b','b','g']

# draw
ax.bar3d(x, y, z, dx, dy, dz, color=colors, alpha=1.0)

# perspective
ax.view_init(azim=48.0, elev=20.0) # problem
#ax.view_init(azim=48.0, elev=45.0) # no problem

# show
plt.show()

2

Miguel,

This is a known issue with mplot3d. The issue is that the polygons are essentially abstracted 2-D objects that are using the same backend architecture as the core 2-D plotting software. I think your example script is probably the best example of the problem that I have seen and does a very good job of illustrating the problem.

The crux of the problem is that each polygon is assigned a z-order for layering, and this z-order is determined by (i think) the center-of-mass location of the polygon and how it relates the location of the centers of mass of the other objects. In most graphing situations, this is a good enough hack, but there are too many use-cases where it falls apart.

Because we are limited to a single z-order value for each object, and compositing is done through a 2-D rendering engine, this problem will likely not get solved any time soon, unfortunately. The fix would probably require a complete rewrite of the mpl drawing engine or maybe the utilization of OpenGL?

Sorry I can’t be more helpful in fixing your problem, it has been a aggravating issue for me as well. Thank you for your excellent example script.

Ben Root

···

On Mon, Nov 22, 2010 at 11:44 AM, Miguel Costa <migueldiascosta@…287…> wrote:

Hello all.

I’m attempting to use bar3d to plot a packing solution but from some

viewpoints the perspective is wrong (boxes seem overlapped), and with a

large number of boxes the plot is always incoherent.

(I’m using matplotlib 1.0.0 on fedora 14)

Does anyone know how to fix this?

Cheers,

Miguel

3

Thank you for your quick (and kind) reply.

I understand that matplotlib is originally 2d - I was hoping, with this new 3d toolkit, to ditch mayavi and use matplotlib for everything :), but that’s ok.

Thanks again,

Miguel

···

On Mon, Nov 22, 2010 at 5:56 PM, Benjamin Root <ben.root@…1304…> wrote:

Miguel,

This is a known issue with mplot3d. The issue is that the polygons are essentially abstracted 2-D objects that are using the same backend architecture as the core 2-D plotting software. I think your example script is probably the best example of the problem that I have seen and does a very good job of illustrating the problem.

The crux of the problem is that each polygon is assigned a z-order for layering, and this z-order is determined by (i think) the center-of-mass location of the polygon and how it relates the location of the centers of mass of the other objects. In most graphing situations, this is a good enough hack, but there are too many use-cases where it falls apart.

Because we are limited to a single z-order value for each object, and compositing is done through a 2-D rendering engine, this problem will likely not get solved any time soon, unfortunately. The fix would probably require a complete rewrite of the mpl drawing engine or maybe the utilization of OpenGL?

Sorry I can’t be more helpful in fixing your problem, it has been a aggravating issue for me as well. Thank you for your excellent example script.

Ben Root