GNUPLOT_CONTOUR, a FreeFem++ script which writes FreeFem++ data to files that Gnuplot can use to create a contour plot.
It's hard enough to figure out how to get FreeFem++ to index the correct data and write it out. It's more than hard enough to try to figure out how to get Gnuplot to try to contour data that is not on a rectangular grid. Thus, I am not surprised that, at the moment, the contour plot that results doesn't make much sense to me.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
You can go up one level to the FreeFem++ web page.