Well, as long as the polys are convex in nature (meaning that they cannot have indentations) then the process is still as I described above. Simply find the mode point (average) of the points, then utilize two of the points in order along with your mode point to extropolate the triangle. Of course if you have concave polys then its another story all together. In witch case take a visit to your local wikipedia and read up. Find the formula you like, and I'm sure we can help you with implementation http://en.wikipedia.org/wiki/Computational_geometry, http://en.wikipedia.org/wiki/Polygon_triangulation, http://en.wikipedia.org/wiki/Point_set_triangulation, or self balancing graph theory (LOL don't look that one up).