#http://www.mathcurve.com/surfaces/bour/bour.shtml
vertices = D1:100 D2:100
t = from 0 to (PI*4) D1
r = from 0 to 2 D2
a = rand2(1, 10)
x = a*(r*cos(t) - r*r*cos(2*t)/2)
y = a*(r*sin(t) - r*r*sin(2*t)/2)
z = 4*a/3*pow(r, 1.5)*cos(1.5*t)
