#http://www.mathcurve.com/surfaces/conederevolution/conederevolution.shtml
vertices = D1:100 D2:100
v = from (-2*PI) to (2*PI) D1
u = from (-PI) to (PI) D2
a = rand2(0, PI*0.45)
x = a*(cos(v) + cos(u))
z = a*(sin(u) + sin(v))
y = 2*a*cot(a)*cos((u-v)/2)
