#http://www.mathcurve.com/surfaces/dini/dini.shtml

vertices = D1:100 D2:100

v = from (-PI) to (PI) D1
u = from (-PI) to (PI) D2

a = 10
k = rand2(0.5, 2)

x = a*cos(v)/ch(u)
z = a*sin(v)/ch(u)
y = a*(u - th(u) + k*v)
