%% 
%%  A DANTE-Edition example
%% 
%%  Example 16-03-5 on page 238.
%% 
%%  Copyright (C) 2011 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[]{article}
\pagestyle{empty}
\setlength\textwidth{129.70511pt}
\setlength\parindent{0pt}

\usepackage{pstricks,pst-node}\SpecialCoor
\makeatletter \def\nodeBetween(#1)(#2)#3{%
 \pst@getcoor{#1}\pst@tempa\pst@getcoor{#2}\pst@tempb
 \pnode(! \pst@tempa /YA exch \pst@number\psyunit div def
  /XA exch \pst@number\psxunit div def
  \pst@tempb /YB exch \pst@number\psyunit div def
  /XB exch \pst@number\psxunit div def
  XB XA add 2 div YB YA add 2 div){#3}}\makeatother

\begin{document}
\begin{pspicture}[showgrid](3,2)
\psline[linestyle=dashed]{o-o}(0.25,0.33)(2.333,2)
\nodeBetween(0.25,0.33)(2.333,2){centre}\pscircle*(centre){3pt}
\end{pspicture}
\end{document}