%% syntaxe : vect1 vect2 angle3d
/angle3d {
4 dict begin
   normalize3d /vect2 defpoint3d
   normalize3d /vect1 defpoint3d
   /cosalpha vect1 vect2 scalprod3d def
   /sinalpha vect1 vect2 vectprod3d norme3d def
   sinalpha cosalpha atan
end
} def