[Tex/LaTex] Image with axis

graphicspgfplotspgfplotstabletikz-pgf

I need to plot some data in a file (10000 records of 2 points each one) but PGFPlots is very very slow rendering it. So I'm trying to use MatLab to plot the data, capture the image without axis and in a tikzpicture render the image with axis.

Here is my test with an 96 x 96 PNG image:

enter image description here

\documentclass{article}

\usepackage{pgfplots}

\begin{document}
  \pgfdeclareimage[width=5cm]{fondo}{avatarMSM.png}
  \begin{tikzpicture}
    \draw node[anchor=south west] (nodoFondo) at (axis cs:0,0) {\pgfuseimage{fondo}};
    \begin{axis}[
        width=5cm,
        scale only axis,
        enlargelimits=false,
        xmin=0,
        xmax=96,
        ymin=0,
        ymax=96,
        axis equal=true
        ]

      \addplot[thick,blue] (0,0) -- (axis cs:96,96);
    \end{axis}
  \end{tikzpicture}
\end{document}

enter image description here

The result has white margins around the image and I can't fit the axis.

Best Answer

Since you are using pgfplots to generate the axis, you can use its built-in method \addplot graphics to align the axis on top of the graphics.

What you need is to define the lower-left and the upper-right corner of the axis -- if your image has a tight bounding box, that's all. If it does not have a tight bounding box, you may want to consult the pgfplots manual section "Using External Graphics as Plot Sources" for more information.

The result looks like this:

\documentclass{article}

\usepackage{pgfplots}

\begin{document}
  \begin{tikzpicture}
    \begin{axis}[
        axis on top,% ----
        width=5cm,
        scale only axis,
        enlargelimits=false,
        xmin=0,
        xmax=96,
        ymin=0,
        ymax=96,
        axis equal=true
        ]

      \addplot[thick,blue] graphics[xmin=0,ymin=0,xmax=96,ymax=96] {Dad64.png};
    \end{axis}
  \end{tikzpicture}
\end{document}

enter image description here

With this setup, you can rescale the axis -- and the \addplot graphics command will automatically rescale the graphics to fit between the designated coordinates.

The feature also supports 3d graphics + 3d axes (with much more input from your side, however).


To make the axis automatically resize to fit the picture while respecting the aspect ratio of the image, you should set axis equal image. Specifying a width or height for the axis will scale the axis and image. In addition to drawing an axis, you can also use this setup to place other TikZ nodes and paths using the image coordinate system. Coordinates specified using (axis cs:<x>,<y>) refer to the image coordinate system:

\documentclass{article}
\usepackage{pgfplots}


\begin{document}
\begin{tikzpicture}
\begin{axis}[enlargelimits=false, axis on top, axis equal image]
\addplot graphics [xmin=0,xmax=96,ymin=0,ymax=96] {Dad64};
\node at (axis cs:49,30) [
    circle,
    draw,
    red,
    thick,
    minimum size=3ex,
    pin={[pin edge=thick]-10:Nose}
] {};
\end{axis}
\end{tikzpicture}
\begin{tikzpicture}
\begin{axis}[enlargelimits=false, axis on top, axis equal image, width=6cm]
\addplot graphics [xmin=0,xmax=96,ymin=0,ymax=96] {Dad64};
\end{axis}
\end{tikzpicture}
\end{document}
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