#http://mathworld.wolfram.com/KuenSurface.html

vertices = D1:100 D2:100

u = from  (-PI*1.6) to (PI*1.6) D1
v = from (PI*0.01) to (PI*0.99) D2

a = sin(u)
b = cos(u)
c = sin(v)
d = cos(v)

t = 1 + u*u*c*c

x = 2*(b + u*a)*c/t
z = 2*(a + u*b)*c/t
y = ln[tan(v/2)] + 2*d/t

y = limit(y, -50, 50)
