%% 
%%  Ein Beispiel der DANTE-Edition
%% 
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{190.324pt}
\setlength\parindent{0pt}
\StartShownPreambleCommands
\usepackage{pstricks,pst-node,pst-xkey}\SpecialCoor
\makeatletter
\define@boolkey[psset]{}[Pst@]{zeigeSP}[true]{}% Schwerpunkt markieren?
\psset{zeigeSP=true}                     % Vorgabe
\def\Schwerpunkt{\pst@object{Schwerpunkt}}
\def\Schwerpunkt@i(#1)(#2)(#3)#4{%
  \pst@getcoor{#1}\pst@tempA% Punkt A    % hole Kordinaten als x y
  \pst@getcoor{#2}\pst@tempB% Punkt B    %  "
  \pst@getcoor{#3}\pst@tempC% Punkt C    %  "
  \begin@SpecialObj                      % Parameter setzen
  \pnode(!%                              % setze Knoten
     \pst@tempA /YA exch \pst@number\psyunit div def
     /XA exch \pst@number\psxunit div def % x y in user Koordinaten
     \pst@tempB /YB exch \pst@number\psyunit div def
     /XB exch \pst@number\psxunit div def
     \pst@tempC /YC exch \pst@number\psyunit div def
     /XC exch \pst@number\psxunit div def
     XA XB XC add add 3.0 div            % xSP
     YA YB YC add add 3.0 div            % ySP
  ){#4}                                  % #5 = Knotenname
  \ifPst@zeigeSP\qdisk(#4){2pt}\fi% markieren?
  \end@SpecialObj%
  \ignorespaces}
\makeatother
\StopShownPreambleCommands
\begin{document}
\begin{pspicture}[showgrid](4,4)  \psset{linewidth=2pt}
  \pspolygon[linecolor=red](0,0)(2,4)(4,0)%
  \Schwerpunkt[zeigeSP,linecolor=red](0,0)(2,4)(4,0){SP1}%
  \pnode(0,0){A}\pnode(0,4){B}\pnode(4,2){C}%
  \pspolygon[linecolor=blue](A)(B)(C)%
  \Schwerpunkt(A)(B)(C){SP2}%
  {\psset{linecolor=blue}\qdisk(SP2){2pt}}
  \ncline[linewidth=0.2pt]{<->}{SP1}{SP2}%
\end{pspicture}
\end{document}
