title: Matplotlib - Wrong overlapping when plotting two 3D surfaces on the same axes
body: <p>I am trying to plot two 3D surfaces on the same axes in matplotlib with the plot_surface command.</p>
  
  <pre><code>fig = plt.figure()
  fig.figsize = fig_size
  ax = fig.gca(projection='3d')
  
  surf = ax.plot_surface(X, Y, Exp_Fric_map, alpha = 1, rstride=1, cstride=1, cmap=cm.winter, linewidth=0.5, antialiased=True)
  surf = ax.plot_surface(X, Y, Fric_map, alpha = 1, rstride=1, cstride=1, cmap=cm.autumn,linewidth=0.5, antialiased=True)
  </code></pre>
  
  <p>The problem I have is that when viewing the plot, not always the correct surface is 'on top', for instance in the plot:</p>
  
  <p><img src="https://i.stack.imgur.com/OAUdA.png" alt="Example plot"></p>
  
  <p>in the back corner (200N, 2.5Hz on the axes) the blue-green surface is 'on top' when actually the yellow-red is closer to the viewer. If I rotate the plot:</p>
  
  <p><img src="https://i.stack.imgur.com/KvmlQ.png" alt="Second example plot"></p>
  
  <p>then things look ok now, the blue-green surface is underneath the yellow-red one at 200N and 2.5Hz (now on the left side). I have tried searching stackoverflow and Google but cannot find any similar problems with a solution.</p>
  
  <p>I am using Python 2.7.3, Numpy 1.6.1 and Matplotlib 1.1.1rc on Linux.</p>