Adding 2d graphics on 3d graphic 2

r=(%pi):-0.01:0;x=r.*cos(10*r);y=r.*sin(10*r);
deff('[z]=surf(x,y)','z=sin(x)*cos(y)');
t=%pi*(-10:10)/10;
fplot3d(t,t,surf,35,45,'X@Y@Z',[-12,2,3]);
        z=sin(x).*cos(y);
z=sin(x).*cos(y);
[x1,y1]=geom3d(x,y,z);
xpoly(x1,y1,'lines');
[x1,y1]=geom3d([0,0],[0,0],[5,0]);
xsegs(x1,y1);
xstring(x1(1),y1(1)," The point (0,0,0)');
xtitle('plot3d and use of xgeom ',' ',' ');