title: pcolormesh with missing values?
body: <p>I have 3 1-D ndarrays: x, y, z</p>
  
  <p>and the following code:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  import scipy.interpolate as spinterp
  
  ## define data
  npoints = 50
  xreg = np.linspace(x.min(),x.max(),npoints)
  yreg = np.linspace(y.min(),y.max(),npoints)
  X,Y = np.meshgrid(xreg,yreg)
  Z = spinterp.griddata(np.vstack((x,y)).T,z,(X,Y),
                        method='linear').reshape(X.shape)
  
  ## plot
  plt.close()
  ax = plt.axes()
  col = ax.pcolormesh(X,Y,Z.T)
  plt.draw()
  </code></pre>
  
  <p>My plot comes out blank, and I suspect it is because the method='linear' interpolation comes out with nans. I've tried converting to a masked array, but to no avail - plot is still blank. Can you tell me what I am doing wrong? Thanks.</p>