\documentclass{article}
% translate with >> pdflatex -shell-escape <file>

% This file is used as unit test for pgfplots, copyright by Christian Feuersaenger.
% 
% See
%   http://pgfplots.sourceforge.net/pgfplots.pdf
% for pgfplots.
%
% Any required input files (for <plot table> or <plot file> or the table package) can be downloaded
% at
% http://www.ctan.org/tex-archive/graphics/pgf/contrib/pgfplots/doc/latex/
% and
% http://www.ctan.org/tex-archive/graphics/pgf/contrib/pgfplots/doc/latex/plotdata/

\usepackage{pgfplots}
\pgfplotsset{compat=1.4}

\usepgfplotslibrary{patchplots}

\pagestyle{empty}

\begin{document}
\pgfplotsset{show nodes/.style={nodes near coords=\coordindex,nodes near coords align={center}}}
	 \def\xA{0} \def\yA{0} % 1
	 \def\xB{3} \def\yB{1} % 5
	 \def\xC{6} \def\yC{1} % 2
	 \def\xD{6} \def\yD{3} % 6
	 \def\xE{5} \def\yE{5} % 3
	 \def\xF{2} \def\yF{6} % 7
	 \def\xG{-1}\def\yG{5} % 4
	 \def\xH{0} \def\yH{3} % 8

	 \def\xM{3} \def\yM{3.75} % new middle node
	 \let\xI=\xM \let\yI=\yM
\begin{tikzpicture}
	\begin{axis}[title={PGFPlots biquadratic (flat)},show nodes]
	\addplot[patch,patch type=biquadratic,point meta=explicit] coordinates {
		(\xA,\yA) [1] 
		(\xC,\yC) [0]
		(\xE,\yE) [0]
		(\xG,\yG) [0]
		(\xB,\yB) [0]
		(\xD,\yD) [0]
		(\xF,\yF) [0]
		(\xH,\yH) [0]
		(\xI,\yI) [0]
	};
	\end{axis}
	\end{tikzpicture}
\end{document}
