> with(plots):with(plottools):
r:=cos(t):
x:=r*cos(s):y:=r*sin(s):z:=sqrt(1-r^2):
a:=plot3d([x,y,z],s=t..2*Pi-t,t=0..Pi/2,scaling=constrained):
b:=plot3d([x,y,-z],s=t..2*Pi-t,t=0..Pi/2,scaling=constrained):
c:=display(a,b):

> c;

> vrml(c,"d:/040/12/12-6.wrl",background_color=white):

>