\documentclass[12pt]{article}% Manuel Luque 
\usepackage{pstricks}
\usepackage{pst-eucl}
\pagestyle{empty}

\begin{document}
\begin{center}
\psset{unit=2cm}
\pspicture(-2.5,-2)(2,2.5)
\pstTriangle(-2,-1){A}(1,2){B}(2,0){C}
% les médiatrices
{% encapsulation de modif paramètres
  \psset{linestyle=none, PointSymbolB=none}
  \pstMediatorAB[PointNameB={}]{A}{B}{K}{KP}\uput{50pt}[-45](KP){KP}
  \pstMediatorAB[PointNameB={}]{C}{A}{J}{JP}\uput{-50pt}[100](JP){JP}
  \pstMediatorAB[PosAngleA=75,PointNameB={}]{B}{C}{I}{IP}\uput{-5pt}[210](IP){IP}
}% fin
\pstInterLL[PointSymbol=square, PosAngle=-170]{I}{IP}{J}{JP}{O}
{% encapsulation de modif paramètres
  \psset{nodesep=-.8, linecolor=green}
  \pstLineAB{O}{I}\pstLineAB{O}{J}\pstLineAB{O}{K}
}% fin
\pstCircleOA[linecolor=red]{O}{A}
% pour que le symbol de O soit sur et non sous les droites
\psdot[dotstyle=square](O)
% les hauteurs et l'orthocentre
\pstProjection{B}{A}{C}{C'}
\pstProjection{B}{C}{A}{A'}
\pstProjection{A}{C}{B}{B'}
\psset{linecolor=blue}\ncline{A}{A'}\ncline{C}{C'}\ncline{B}{B'}
\pstInterLL[PointSymbol=square]{A}{A'}{B}{B'}{H}
% les médianes et le centre de gravité
\psset{linecolor=magenta}\ncline{A}{I}\ncline{C}{K}\ncline{B}{J}
\pstCGravABC[PointSymbol=square, PosAngle=95]{A}{B}{C}{G}
\endpspicture
\end{center}

\end{document}%

