[Tex/LaTex] Combining Surface plots with contour plots

gnuplotpgfplotspgfplotstabletikz-pgf

I am drawing a surface plot in pgfplots from some data file (working quite well).

Afterwards, I want to draw a contour plot on top of the surface plot, to simulate kind of a filled contour plot.

At the moment, I have to issues:

  • Some error during compilation: ! Package PGF Math Error: Could not parse input '' as a floating point number, sorry. The unreadable part was near ''..

  • The contour lines are connected in wrong ways instead of being interupted (in this example for the -50 isoline)

Since I've never worked with gnuplot or the contourplot options before, I have no idea how to get rid of the error.

The code:

\documentclass{standalone}
\usepackage{pgfplots,pgfplotstable}
\usepgfplotslibrary{colormaps}
\pgfplotsset{compat=newest}

\begin{filecontents}{min.txt}
f v p
3.400E1 0.500 -58.174
3.400E1 0.600 -36.901
3.400E1 0.700 -35.791
3.400E1 0.800 -65.193
3.600E1 0.500 -45.351
3.600E1 0.600 -36.959
3.600E1 0.700 -43.273
3.600E1 0.800 -78.534
3.800E1 0.500 -64.744
3.800E1 0.600 -42.736
3.800E1 0.700 -45.362
3.800E1 0.800 -80.150
\end{filecontents}

\begin{document}


\pgfplotsset{colormap/steep/.style={
 colormap={steep}{[1cm]rgb255(0cm)=(255,255,255) rgb255(27cm)=(255,255,254) rgb255(28cm)=(1,0,0) rgb255(42cm)=(0,0,0)
}}}

\begin{tikzpicture}
\begin{axis}[
             z buffer = sort,
             grid=major, 
             axis on top,
             colorbar,
             colormap/viridis,
             mesh/ordering=x varies,
             view={0}{90},  
             tick label style={/pgf/number format/fixed},
             enlargelimits=false,
             xlabel={$x$}, 
             ylabel={$y$}, 
            ]
  \pgfplotstableread{min.txt}\datatable
  % underlying surface plot
  \addplot3[
            mesh/rows=3, 
            surf,  
            shader = interp,         
           ] table [
                    x index = 1,
                    y  index= 0,
                    z index = 2,
                            ]   from \datatable {};
  % contour on top
  \pgfplotsset{contour/every contour label/.style = {
               sloped,
               transform shape,
               every node/.style={
                                 mapped color,
                                 fill=none,
                                },
              },}
  \addplot3[
            mesh/rows=3, 
            mesh/cols=4, 
            colormap/steep,
            contour gnuplot={
                             levels={-65,-50,-40,-35},
            },
            contour/label distance=130pt,
            samples=500,
            contour/labels over line,
           ] table [
                    x index = 1,
                    y  index= 0,
                    z index  = 2,
                   ]   from \datatable {};
\end{axis}
\end{tikzpicture}
\end{document}

Result, if the occurring errors are ignored:
enter image description here

For higher resolution input data, the problem gets even worse.
There seem to appear breaks in the contour lines in addition to the wrong connections. But this might be just a symptom of the same error…

enter image description here

Best Answer

The graphics issues (overlapping contours) are a follow-up issue of the compilation problems.

I enabled debug output and realized that they are due to z buffer=sort which appears to result in wrong output when used with contour gnuplot.

I removed z buffer=sort and all is fine. I will improve the robustness of pgfplots such that z buffer =sort will be ignored for contour plots.

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