Align axis of separate plots in pgfplots

Question

I am preparing a talk using plots generated in pgfplots' axis-environment. I want the plots' axes to be of the exact same size and position. Unfortunately, plots with different axis- and plot-labels differ in size and produce small "jumps" when flipping through the pages of the presentation. In the code below, I illustrate the problem. The axes have the same size, but due to the different labels, their horizontal position shifts. If one comments the varwidthoption, one can see, that the same thing happens in the vertical direction.

\documentclass[crop,10pt,
varwidth=250pt
]{standalone}
\usepackage[english]{babel}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}
\begin{document}

\begin{tikzpicture}
  \begin{axis}[
  width=200pt,
  heigth=200pt,
  xmin=0,xmax=1,ymin=0,ymax=1,
  xlabel=xlabel,
  ylabel=ylabel,
  scale only axis
  ]
  \addplot coordinates{ 
  (0.1,0.1)
  (0.9,0.9)
  };
  \end{axis}
\end{tikzpicture}
\begin{tikzpicture}
  \begin{axis}[
  width=200pt,
  heigth=200pt,
  xmin=0,xmax=100,ymin=0,ymax=100,
  xlabel=x$_l^a$bel,
  ylabel=y$_l^a$bel,
  scale only axis,
  ]
  \addplot coordinates{ 
  (10,10)
  (90,90)
  };
  \end{axis}
\end{tikzpicture}

\end{document}

Is there a way to produce separate plots with axes of exact same size and position?

Answer 1

I think section 4.20 The Picture’s Size: Bounding Box and Clipping of the pgfplots manual (v1.10) might be of use, you can use the overlay style specification to exclude parts from the bounding box, thus aligning only the axes themselves, regardless of the size of the labels.

\documentclass{article}
\usepackage[english]{babel}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}
\begin{document}
\begin{center}
\begin{tikzpicture}
  \begin{axis}[
    width=200pt,
    height=200pt,
    xmin=0,xmax=1,ymin=0,ymax=1,
    xlabel=xlabel,
    ylabel=ylabel,
    ylabel style={overlay},
    yticklabel style={overlay},
    xlabel style={overlay},
    xticklabel style={overlay},
    scale only axis
    ]
    \addplot coordinates{
      (0.1,0.1)
        (0.9,0.9)
    };
\end{axis}
\end{tikzpicture}
\end{center}
\vspace*{4em}
\begin{center}
\begin{tikzpicture}
\begin{axis}[
  width=200pt,
  height=200pt,
  xmin=0,xmax=100,ymin=0,ymax=100,
  xlabel=x$_l^a$bel,
  ylabel=y$_l^a$bel,
  ylabel style={overlay},
  yticklabel style={overlay},
  xlabel style={overlay},
  xticklabel style={overlay},
  scale only axis,
  ]
  \addplot coordinates{
    (10,10)
      (90,90)
  };
\end{axis}
\end{tikzpicture}
\end{center}
\end{document}

Answer 2

Thanks to @hugovdberg I was able to find a solution. One can use the calc library to define coordinates relative to the plot's axis and then use \path[use as bounding box] (first coordinate) rectangle (second coordinate); to create the bounding box. The following code will produce the desired result. The bounding box is drawn for illustration.

\documentclass[10pt]{beamer}
\usepackage[english]{babel}
\usepackage{pgfplots}
\usetikzlibrary{calc}
\pgfplotsset{compat=1.9}
\begin{document}
\begin{frame}
\begin{tikzpicture}
  \begin{axis}[
  width=150pt,
  height=150pt,
  xmin=0,xmax=1,ymin=0,ymax=1,
  xlabel=xlabel,
  ylabel=ylabel,
  scale only axis,
  ]
  \addplot coordinates{ 
  (0.1,0.1)
  (0.9,0.9)
  };
  \end{axis}
  \coordinate (topleft) at ($(current axis.north west) + (-1.3cm,0.3cm)$);
  \coordinate (bottomright) at ($(current axis.south east) + (0.4cm,-1cm)$);
  \path[use as bounding box,draw] (topleft) rectangle (bottomright);
\end{tikzpicture}
\end{frame}
\begin{frame}
\begin{tikzpicture}
  \begin{axis}[
  width=150pt,
  height=150pt,
  xmin=0,xmax=100,ymin=0,ymax=100,
  xlabel=x$_l^a$bel,
  ylabel=y$_l^a$bel,
  scale only axis,
  ]
  \addplot coordinates{ 
  (10,10)
  (90,90)
  };
  \end{axis}
  \coordinate (topleft) at ($(current axis.north west) + (-1.3cm,0.3cm)$);
  \coordinate (bottomright) at ($(current axis.south east) + (0.4cm,-1cm)$);
  \path[use as bounding box,draw] (topleft) rectangle (bottomright);
\end{tikzpicture}
\end{frame}
\end{document}