a = 1
b = 0
c = 0
f = lambda t: ((a*c*cos(t) - b*sin(t))/sqrt(a^2+b^2), (b*c*cos(t) + a*sin(t))/sqrt(a^2+b^2), cos(t)*sqrt(a^2+b^2))
t = Tachyon(camera_center=(0,0,0))
t.texture('t')
t.light((-20,-20,40), 0.2, (1,1,1))
t.parametric_plot(f,0,2*pi,'t',min_depth=6)
t.show()
