Draw invisible axes with visible labels

Question

I was fiddling with how to plot raw signals to LaTeX and it turned out that there is no good solution (tikzexternalize, R+kniter, matlatb2tikz are cool but exhaust TeX memory if is really raw data)... Anyway, I decided to go with MATLAB right away and export the plots as PDFs without labels or ticks, which I intended to add/draw on to of the image. Now there's the problem:

How to draw an invisible frame and tick marks? I need the ticks for the ticklabels so hide axis is not an option. I feel that this is some pgfplot style-thing, which is totally out of my skills.

\documentclass{article}
\usepackage{pgfplots}

\pgfplotsset{compat=1.17}
\begin{document}
    \begin{figure}
        \begin{tikzpicture}
        \node[anchor=south west,inner sep=0cm] at (0,0) {\includegraphics[width=\textwidth]{constant-plot.png}};
        \begin{axis}[
                scale only axis,
                width = 9.65cm,
                height = 7.93cm,
                xshift=1.84cm,
                yshift=1.47cm,
                xmin=-0.1,
                xmax=1.1,
                ymin=0.05,
                ymax=0.7,
                ytick={0.2,0.4,...,0.6},
                color=green,
                every tick/.style={green}
                ]
        \end{axis}
        \end{tikzpicture}
    \end{figure}
\end{document}

I just took a png from pgfplots.net.

I have no idea if that is a proper way to link external graphics with Tex-based fonts/labeling but I don't see a different option.

Answer 1

Just add axis line style={opacity=0}.

\documentclass{article}
\usepackage{pgfplots}

\pgfplotsset{compat=1.17}
\begin{document}
    \begin{figure}
        \begin{tikzpicture}
        \node[anchor=south west,inner sep=0cm] at (0,0)
         {\includegraphics[width=\textwidth]{example-image-duck}};
        \begin{axis}[axis line style={opacity=0},
                scale only axis,
                width = 9.65cm,
                height = 7.93cm,
                xshift=1.84cm,
                yshift=1.47cm,
                xmin=-0.1,
                xmax=1.1,
                ymin=0.05,
                ymax=0.7,
                ytick={0.2,0.4,...,0.6},
                color=green,
                every tick/.style={green}
                ]
        \end{axis}
        \end{tikzpicture}
    \end{figure}
\end{document}

However, from your description you may be looking for 4.3.7 Using External Graphics as Plot Sources.

Answer 2

Disclaimer : My answer is more related to the problem of plotting large chunks of data than the technical resolution of the OP. If felt irrelevant, I will happily remove it.

For my thesis, I had quite a similar issue. I developped an overlay based on the matlab2tikz script, unfortunately I can not share it at the moment. However I can help you with the overall strategy I used.

The problem :

• The main issue with raw data is that you tend to overflow tikz or pgfplots capabilities
• However, you do not want matlab to plot the axis, legends or labels, otherwise you wouldn't ask this question.

The strategy :

• Let matlab do the heavy lifting and create the raw plot then remove hide the axis and associated graphics. For this operation, I used the export_fig package, which has the ability to export png plots without most flaws of the matlab printing process.

• Insert the printed image in a pgfplots axis using a graphics plot

  \addplot[] graphics[xmin=...,xmax=...,ymin=...,ymax=...] {path/to/your/picture};

as described in the pgfplots manual section 4.3.7 (v1.16)

With my custom script what I basically do is

1. Plot everything
2. Set all axis properties to manual
3. Hide the plot of the data and export it with matlab2tikz
4. Show the plot of the data, hide the axis and print with export_fig
5. Edit the latex document to add the \addplot graphics
6. Enjoy