Centering inside sidewaysfigure with footnote

Question

I am using sidewaysfigure environment to rotate my figures. However, they are not centered in the middle of the page. I can't use \centering since I want that my footnote is "left aligned".

Here is a short example:

\documentclass[a4paper,12pt]{scrartcl}
\usepackage[ngerman]{babel}
\usepackage{amsthm}
\usepackage{mathtools}

\usepackage{rotating}
 \usepackage{float}


\begin{document}
\begin{sidewaysfigure}
\caption{Fill}
 \includegraphics[width=0.9\paperwidth]{example-image-c}
 \footnotesize 

 A long footnote
  \label{fig:fill}
\end{sidewaysfigure}
\end{document}

The output of my "real example" with the code mentioned in the comments:

The caption should be aligned in the same height as the footnote.

Answer 1

There are a number of ways to achieve centering, or to overcome \centering. Centering is achieved by setting \leftskip and \rightskip to \hfil (more of less). You can also center an image by adding \hfil to the left (and \par to the right), or \hfill before and after. One can overcome \centering using \parbox{\linewidth}{...} or \makebox[\linewidth][l]{...}.

BTW, inserting \hfil between subfigures has a nice effect too.

You also might consider using afterpage and pdflscape instead of sidewaysfigure (It displays the page so that the image is right-side-up.)

\documentclass[a4paper,12pt]{scrartcl}
\usepackage[ngerman]{babel}
\usepackage{amsthm}
\usepackage{mathtools}

\usepackage{rotating}
 \usepackage{float}
\usepackage[format=plain, justification=RaggedRight, singlelinecheck=false]{caption}
\usepackage{showframe}

\begin{document}
\begin{sidewaysfigure}
\caption{Fill}\label{fig:fill}
\hfil\includegraphics[width=0.8\linewidth]{example-image-c}% center inamge only

\footnotesize A long footnote
\end{sidewaysfigure}

\begin{sidewaysfigure}
\centering
\caption{Fill}\label{fig:fill}
\includegraphics[width=0.8\linewidth]{example-image-c}
\parbox{\linewidth}{\footnotesize A long footnote}% justify footnote
\end{sidewaysfigure}
\end{document}

Answer 2

Measure the image and use a suitably sized tabular:

\documentclass[a4paper,12pt]{scrartcl}
\usepackage[ngerman]{babel}
\usepackage{amsthm}
\usepackage{mathtools}
\usepackage{rotating}

\newsavebox{\imagebox}

\begin{document}

\begin{sidewaysfigure}
\centering
\caption{Fill}\label{fig:fill}

\sbox{\imagebox}{\includegraphics[width=0.9\paperwidth]{example-image-c}}
\begin{tabular}{@{}p{\wd\imagebox}@{}}
\usebox{\imagebox} \\
\footnotesize  A long footnote, long footnote, long footnote,
long footnote, long footnote, long footnote, long footnote,
long footnote, long footnote, long footnote, long footnote,
long footnote, long footnote
\end{tabular}
\end{sidewaysfigure}

\end{document}

Note that the \label refers to \caption, so it's best placed near it.

A different realization with the caption left aligned with respect to the image:

\documentclass[a4paper,12pt]{scrartcl}
\usepackage[ngerman]{babel}
\usepackage{amsthm}
\usepackage{mathtools}
\usepackage{rotating}
\usepackage{ragged2e}
\usepackage[
  format=plain,
  justification=RaggedRight,
  singlelinecheck=false
]{caption}

\newsavebox{\imagebox}

\begin{document}
\begin{sidewaysfigure}
\centering

\sbox{\imagebox}{\includegraphics[width=0.9\paperwidth]{example-image-c}}

\begin{minipage}{\wd\imagebox}
\caption{Fill}\label{fig:fill}

\usebox{\imagebox}

\footnotesize  A long footnote, long footnote, long footnote,
long footnote, long footnote, long footnote, long footnote,
long footnote, long footnote, long footnote, long footnote,
long footnote, long footnote

\end{minipage}
\end{sidewaysfigure}

\end{document}