Positioning pgfplots axis in tikzpicture

Question

I want to put a pgfplots plot beside several other pdf images that I import into my document, but I can't figure out how to position the pgfplots axis in the larger tikzpicture:

\documentclass{article}

\usepackage{graphicx}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}

\begin{document}
\begin{figure*}

  \begin{center}
    \begin{tikzpicture}

       \node[anchor=south west] (img) at (0,0) 
            {\includegraphics[width=0.3\linewidth]{1.pdf}};
       \node[anchor=south west] 
            at (0.01\linewidth,0.01\linewidth) {a};        

       \node[anchor=south west] (img) at (0.33\linewidth,0) 
            {\includegraphics[width=0.3\linewidth]{1.pdf}};
       \node[anchor=south west] 
            at (0.34\linewidth,0.01\linewidth) {b}; 

       \begin{axis}[width=0.45\linewidth, yticklabels={}]
         \addplot [const plot, fill=red] 
                  table [x index=0, y index=1]
                  {hist.txt}
         \closedcycle;  
       \end{axis}

    \end{tikzpicture}
  \end{center}

  \caption{\label{detdemo}An example of my output}
\end{figure*}
\end{document}

here is the example output:

The axis seems to begin from the (0,0) of the tikzpicture.

I wanted to see how I can position this axis after the second picture? Such that its bottom left corner is on (0.66\linewidth,0).

Answer 1

You can define the coordinate for the lower left corner of the axis with the at key,

at={(0.66\linewidth,0)}

Add this to the axis options.

\documentclass{article}

\usepackage{graphicx}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}

\begin{document}
\begin{figure*}

  \begin{center}
    \begin{tikzpicture}

       \node[anchor=south west] (img) at (0,0) 
            {\includegraphics[width=0.3\linewidth]{example-image-a}};
       \node[anchor=south west] 
            at (0.01\linewidth,0.01\linewidth) {a};        

       \node[anchor=south west] (img) at (0.33\linewidth,0) 
            {\includegraphics[width=0.3\linewidth]{example-image-b}};
       \node[anchor=south west] 
            at (0.34\linewidth,0.01\linewidth) {b}; 

       \begin{axis}[width=0.45\linewidth, yticklabels={},at={(0.66\linewidth,0)}]
         \addplot [const plot, fill=red] 
                  {x}
         \closedcycle;  
       \end{axis}

    \end{tikzpicture}
  \end{center}

  \caption{\label{detdemo}An example of my output}
\end{figure*}
\end{document}

Answer 2

As a quick hack, you can either use a scope with a proper xshift or put the axis inside another node.

\documentclass{article}

\usepackage{graphicx}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}
\usetikzlibrary{positioning}

\begin{document}
\begin{figure*}

  \begin{center}
    \begin{tikzpicture}

       \node[anchor=south west] (img1) at (0,0)
            {\includegraphics[width=0.3\linewidth]{example-image-a}};
       \node[anchor=south west]
            at (0.01\linewidth,0.01\linewidth) {a};

       \node[anchor=south west] (img2) at (0.33\linewidth,0)
            {\includegraphics[width=0.3\linewidth]{example-image-b}};
       \node[anchor=south west]
            at (0.34\linewidth,0.01\linewidth) {b};
       \begin{scope}[xshift=0.66\linewidth] 
       \begin{axis}[width=0.45\linewidth, yticklabels={}]
         \addplot [const plot, fill=red]
                  {x}       %% I changed this change it back
         \closedcycle;
       \end{axis}
       \end{scope}

    \end{tikzpicture}
  \end{center}

  \caption{\label{detdemo}An example of my output comes here}
\end{figure*}
\end{document}

But it will be better if you use another tikzpicture environment IMO.