title: Interpolation over an irregular grid
body: <p>So, I have three numpy arrays which store latitude, longitude, and some property value on a grid -- that is, I have LAT(y,x), LON(y,x), and, say temperature T(y,x), for some limits of x and y.  The grid isn't necessarily regular -- in fact, it's tripolar.</p>
  
  <p>I then want to interpolate these property (temperature) values onto a bunch of different lat/lon points (stored as lat1(t), lon1(t), for about 10,000 t...) which do not fall on the actual grid points.  I've tried matplotlib.mlab.griddata, but that takes far too long (it's not really designed for what I'm doing, after all).  I've also tried scipy.interpolate.interp2d, but I get a MemoryError (my grids are about 400x400).</p>
  
  <p>Is there any sort of slick, preferably fast way of doing this?  I can't help but think the answer is something obvious...  Thanks!!</p>