title: How do I generate a contour graph?
body: <p>How do I generate a contour graph like this:
  <a href="http://www.fz-juelich.de/vislab/software/gsharp/Gsharp/userguide/interpolate/ex6.gif" rel="nofollow noreferrer">contour http://www.fz-juelich.de/vislab/software/gsharp/Gsharp/userguide/interpolate/ex6.gif</a></p>
  
  <p>It's easy enough if the points are on a regular grid, but what if they aren't, like in my example? Is there a fairly simple algorithm to determine the color for each pixel?</p>