[pstricks] Involute curve

[Michael Sharpe]

I made some example code for drawing an involute to a (polyline  
approximation to ) a given curve. The file is at

http://math.ucsd.edu/~msharpe/involute.tex

I am not completely satisfied with the code, as it has some add hoc  
features, and I was unable to keep track of the radius for the  
successive curves by means of a Postscript variable, rather than on  
the stack. If you have any suggestions for improvement, I'd be happy  
to receive them.

Michael