anneau_gouttiere.tex

\documentclass{article}
\usepackage{pst-solides3d}
\begin{document}
\pagestyle{empty}
 
\newcommand\SectionJante{
   90 10 270{
      /Angle exch def
      R r sub Angle cos mul R add % y=(R-r)cos(A) + R
      R r sub Angle sin mul       % z=(R-r)sin(A)
   } for
   R h 2 div neg                  % (y=R, z=-h/2)
   R h 2 div neg h 6 div add      % (y=R, z=-h/2+h/6)
   270 -10 90 {
      /Angle exch def
      R r sub h 6 div sub Angle cos mul R add % y=(R-r-h/6)cos(A)+ R
      R r sub h 6 div sub Angle sin mul       % z=(R-r)-h/6sin(A)
   } for
   }
 
\begin{center}
\begin{pspicture}(-5,-4)(5,4)
\psframe*[linecolor=blue!20](-5,-4)(5,4)
\psset[pst-solides3d]{SphericalCoor,viewpoint=70 40 30,Decran=25,lightsrc=100 30 100}
\psSolid[object=anneau,section=\SectionJante,h=8,R=12,r=8]%
\end{pspicture}
\end{center}
 
\end{document}