数学图形(2.17)pappus螺线

帕波斯(Pappus of Alexandria) 生于亚历山大,活跃于公元300—350前后.该螺线是一种绕在圆锥上的曲线.

#http://www.mathcurve.com/courbes3d/spiraleconic/pappus.shtml

vertices = 

t = from (-*PI) to (*PI)

r =
a = rand2(PI*0.2, PI*0.8)

x = r*sin(a)*t*cos(t)
z = r*sin(a)*t*sin(t)
y = r*cot(a)*t

另一种写法:

vertices = 

t = from (-*PI) to (*PI)

r =
a = rand2(PI*0.1, PI*0.9)

x = r*t*sin(a)*cos(t)
y = r*t*cos(a)
z = r*t*sin(a)*sin(t)