#http://www.2dcurves.com/sextic/sextick.html

vertices = D1:100 D2:100

u = from (-PI/2) to (PI/2)  D1
v = from 0 to (2*PI) D2

x = sin(u)
a = 0.618
n = a*pow_sign(cos(u), 2.5)

y = n*cos(v)
z = n*sin(v)
