数学图形(2.13)Spherical trochoid曲线

该曲线与上一节的herical cycloid球面外摆曲线 很相似,难道这是球面内摆曲线?

#http://www.mathcurve.com/courbes3d/cycloidspheric/trochoidspheric.shtml

vertices = 

t = from  to (*PI)

a = rand2(0.1, )
b = rand2(0.1, )
d = rand2(0.1, )

q = rand2(0.5, )
w = rand2(PI*0.1, PI*0.9)

s = sin(w)
c = cos(w)

x = (a - b*c + d*c*cos(q*t))*cos(t) + d*sin(t)*sin(q*t)
z = (a - b*c + d*c*cos(q*t))*sin(t) - d*cos(t)*sin(q*t)
y = s*(b - d*cos(q*t))