I just can't figure out how to get the spline surface fitting routine interpolate.bisplrep to work. Specifically, it only seems to work for very particular grid sizes, and gives useless results for most others. In the tutorial, a 20x20 grid is used, but there is no explination how 20x20 is chosen. Most of the other grid sizes I've tried dont' work (e.g 15x15, 16x16, 20x25, 25x20, 25x25). I bought a copy of Dierckx's book, but it contains no practical information on the usage of the FITPACK library. Nor does the web site for FITPACK [http://www.netlib.org/dierckx/index.html] contain any usage information. AFAICT, the FITPACK library (upon which the interpolate module is based) spline surface fitting routine is useless for real-world problems and only suitable for tutorial purposes. Of the 11 grids tried, only 4 produced reasonable results: 13x13, 17x17, 17x19, 20x20. If the goal were to pick a grid by hand to produce a nice graph, it wouldn't be an issue, but I need to be able to fit a surface to a set of points in an automated manner without requiring a human to adjust the grid sizes to get reasonable surface fit. In my application the grid points represent physical data points and it won't be possible to "add more points" to make the library happy, and discarding points is throwing away valuable data. Here's a web page with surface plots for various grid sizes: http://www.visi.com/~grante/scipy/interpolate.html -- Grant Edwards grante@visi.com