Below is the tclet you can use to investigate the iterative scheme described by Barry Lewis.
If you can't get the plugin working then you can download a wish script: 169.tcl
Button-1 -> start creation of points
Button3 -> dynamic zoom (down to start, up to stop)
Skip -> for prettier pictures
Expression -> use p and v to represent the point and a vertex, and a and b to combine them. If no points are created then there is an error in the expression.
$Id: 169-tcl.html,v 1.10 2000/10/19 23:05:14 sjg Exp $