Gnuplot is an open source plotting program which has support for contours and the like. It runs on most different OSs. You can access the functions of this program via Chart::Graph and a plugin, Chart::Graph::Gnuplot directly from perl, producing image file output for further use.

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain