#http://www.mathcurve.com/courbes3d/loxodromie/sphereloxodromie.shtml
vertices = D1:360 D2:100
u = from (-PI) to (PI) D1
v = from (-PI) to (PI) D2
r = 10
x = r*cos(u)/ch(v*u)
y = r*sin(u)/ch(v*u)
z = r*th(v*u)
