%@AUTEUR: Juergen Gilg
\psset{SphericalCoor,viewpoint=50 50 20,lightsrc=25 37 17,Decran=40,unit=0.75}
\begin{pspicture}(-5,-1)(3,15)

 \pstVerb{
 /torsion {
 2 dict begin
 /M defpoint3d % on récupère les coordonnées
 /AngleTorsion M 20 mul 3 -2 roll pop pop def
 % on tourne de 10 degrés à chaque niveau
 M 0 0 AngleTorsion rotateOpoint3d
 end} def}%

  \psSolid[object=grille,
    base=-9 9 -9 9,
    fillcolor=yellow,
    ngrid=24 24,
    ](0,0,0)
 \psSolid[object=cone,r=8,h=10,ngrid=36 24,
% base=1.5 0 1.5 1.5 0 1.5 -1.5 1.5 -1.5 0 -1.5 -1.5 0 -1.5 1.5 -1.5,
 transform=torsion,
 fillcolor=lightgray,
 incolor=lightgray,
 hollow,
 opacity=0.6
 ]%
 \end{pspicture}