title: multiple objects on the same plot (MATPLOTLIB)
body: <p>SHORT QUESTION:
  I'd like to draw different shapes using winged egde strucutre, so I have one class that actually draw any winged eged and another to define a cube and other shapes. Now I want to draw 2 cubes on the same figure but I can't and I always get one cube in each figure.</p>
  
  <p>LONG QUESTION:
  I'd like to draw different shapes using winged egde strucutre, so I have:</p>
  
  <pre><code>class WEdge -&gt; wedge_instance = WEdge(vertices, faces) 
  </code></pre>
  
  <p>and then I have one class for each shape that I need to draw for example:</p>
  
  <pre><code>class Box -&gt; simplebox = Box(vertices, faces, translation, rotation)
  </code></pre>
  
  <p>In the WEdge class I actually plot the objects using the following code: </p>
  
  <pre><code>        ax = a3.Axes3D(pl.figure())
          for k in range(self.nFaces):
             currentColumn = self.faces[k,:]
             vtx = np.zeros([4,3])
             j = 0
             for i in currentColumn:
                 vtx[j] = self.vertices[i-1]
                 j = j +1
          tri = a3.art3d.Poly3DCollection([vtx])
          tri.set_color(colors.rgb2hex(sp.rand(3)))
          tri.set_edgecolor('b')
          ax.add_collection3d(tri)  
  </code></pre>
  
  <p>The problem is when I want to draw two cube in the same figure. I have tried many possible combinations of hold, gca and so on but in the end I get always one cube in Figure 1 and the other in Figure 2.</p>
  
  <p>Example: </p>
  
  <pre><code>&gt;&gt;&gt;Box(3,1,3, [0,1,0], np.eye(3))
  &gt;&gt;&gt; # hold, gca, timer...
  &gt;&gt;&gt;Box(3,1,3, [1,0,3], np.eye(3))
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/aSQ0g.png" alt="Box(3,1,3, [0,1,0], np.eye(3)"><img src="https://i.stack.imgur.com/e0GAr.png" alt="Box(3,1,3, [1,0,3], np.eye(3)"></p>