Fit sidewaysfigure to page width including caption and source

Question

I'm trying to add a sidewaysfigure to my document, but when I set the width to \textwidth it comes out too wide.

This is my code:

\usepackage{rotating}

\begin{sidewaysfigure}
   \centering
   \begin{minipage}{\textwidth}
      \caption{The caption}
      \includegraphics[width=\textwidth]{img/diagramm_hs.png}\\
      \source{The source}
      \label{fig:diagramm_hs}
   \end{minipage}
\end{sidewaysfigure}

And here is the result:

As you can see, the image is wider than the textwidth (textwidth is as wide as the line in the header), especially with the caption and source.

How can I make the image as large as possible on the page while everything, including caption and source, remain in the textarea?

EDIT: The image dimensions are 1327x960 px. This is my documentclass:

\documentclass[
paper=A4,
fontsize=12pt,
BCOR12mm,
DIV14,
parskip=half*,
headsepline,
listof=totoc,
footinclude=false,
headinclude=true,
final
]{scrartcl}

Answer 1

First, the original \textwidth is lost using sidewaysfigure. Second, I needed to test if the total figure was too big. Finally, I needed the image height using [width=\textwidth] in order to determine what [height=] should be to compensate.

I tested \listoffigures to make sure only one caption showed up.

\documentclass{article}
\usepackage{showframe}
\usepackage[Export]{adjustbox}
\usepackage{rotating}
\usepackage{caption}
\captionsetup{justification=raggedright,
               singlelinecheck=false}

\newcommand{\source}[1]{\ttfamily #1}

\newsavebox{\tempbox}
\newlength{\tempdima}
\newlength{\tempdimb}
\newlength{\tempdimc}

\begin{document}
  \tempdima=\textwidth% inside \textwidth=\linewidth=\textheight
  \begin{sidewaysfigure}
  \textheight=\tempdima
  \settoheight{\tempdimb}{\includegraphics[width=\textwidth]{example-image-a}}% default height
  \savebox{\tempbox}{\begin{minipage}{\textwidth}
    \caption{The caption}
    \addtocounter{figure}{-1}% reset
    \rule{\textwidth}{\tempdimb}% same size but faster
    \par\source{The source}
    \end{minipage}}%
  \tempdima=\ht\tempbox\relax% can't get \dimexpr to work
  \advance\tempdima by \dp\tempbox\relax
  \tempdimc=\tempdimb
  \ifdim\textheight<\tempdima
    \advance\tempdimb by \textheight
    \advance\tempdimb by -\tempdima
  \fi
  \tempdima=\dimexpr \tempdimb*\textwidth/\tempdimc\relax% compute scaled width
  \hfil\begin{minipage}{\tempdima}
  \caption{The caption}
  \includegraphics[width=\textwidth]{example-image-a}\par
  \source{The source}
  \end{minipage}
  \end{sidewaysfigure}
\end{document}

Answer 2

As far as I can tell, you haven't provided any information yet about the natural size of the image (or of its natural height to width ratio), the dimensions of the textblock, or even of the document class you use. It's thus not possible to give very specific advice.

All I can think of suggesting is to set the image's width to \textwidth and its height to something like 0.7\textheight; see the screenshot below. Depending on the natural size of the image, you will probably have to adjust the factor 0.7; it may also be useful to set the option keepaspectratio.

\documentclass{report}
\usepackage{caption}
\captionsetup{justification=raggedright,
               singlelinecheck=false}
\usepackage{rotating}
\usepackage[showframe]{geometry}
\begin{document}    

\begin{sidewaysfigure}
   \caption{The caption}
   \label{fig:diagramm_hs}
   \includegraphics[width=\textwidth,
                    height=0.7\textheight,
                    %keepaspectratio  % may need to uncomment this option
                   ]{example-image-a}

   Quelle: The source
\end{sidewaysfigure}
\end{document}

Answer 3

Here is a code that works for me (not perfect but I can work with it):

\documentclass[a4paper,twoside]{article}
\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{rotating}
\usepackage[showframe ,lmargin=1.0783in,rmargin=1.3in,top=2.8cm,bottom=4.15cm]{geometry}
\setlength{\headheight}{40.9461pt}
\usepackage{fancyhdr}
\fancyhead[RE]{}
\fancyhead[RO]{\rightmark}
\fancyhead[LO]{}
\fancyhead[LE]{\leftmark}
\usepackage{hyperref}

\usepackage{lipsum}

%For caption
\def\abcapskip{3.5mm}
\def\belcapskip{4mm}
\usepackage[aboveskip=\abcapskip,belowskip=\belcapskip]{caption}
\renewcommand{\captionfont}{\rmfamily}
\renewcommand{\captionlabelfont}{\bfseries\sffamily}
\captionsetup{labelsep=colon}
\usepackage{amsmath}
\numberwithin{figure}{section}
\renewcommand{\thesection}{\Roman{section}}
\renewcommand{\thefigure}{\thesection.\arabic{figure}}
\newcounter{nextfigure}
\newcommand*{\PhantomTheFigure}{\setcounter{nextfigure}{\value{figure}}\stepcounter{nextfigure}\Roman{section}.\roman{nextfigure}}
%For sidewaysfigure's height
\newsavebox{\capbox}
\newsavebox{\textbox}
\newlength{\swheight}
\newlength{\mywidth}
\newlength{\myheight}
\setlength{\mywidth}{\textwidth}
\setlength{\myheight}{\textheight}
\newcommand{\swcaption}[4][]{\gdef\FArg{#1}\gdef\SArg{#2}\gdef\TArg{#3}\gdef\FthArg{#4}\savebox\capbox{\vbox{{\bfseries\sffamily Figure\space\PhantomTheFigure:}\space\textrm#2}}\savebox\textbox{\vbox{#4}}\setlength{\swheight}{\mywidth}\ifx\SArg\empty\relax\else\addtolength{\swheight}{-\dimexpr\ht\capbox+\dp\capbox+\abcapskip+\belcapskip}\fi\ifx\FthArg\empty\relax\else\addtolength{\swheight}{-\dimexpr\ht\textbox+\dp\textbox}\fi}
\newcommand{\makeswcap}{\ifx\FArg\empty\captionof{figure}{\SArg}\else\captionof{figure}[\FArg]{\SArg}\fi\TArg}
\newcommand{\makeswtext}{\ifx\FArg\empty\relax\else\par\usebox{\textbox}\par\fi}


\begin{document}
\setlength{\mywidth}{\textwidth}
\setlength{\myheight}{\textheight}
\pagestyle{fancy}
\section{First example with caption below}
\lipsum[1-2]

{\color{red}Here comes the Sidewaysfigure~\ref{fig:A1} with the caption below the figure:}

\begin{sidewaysfigure}
  \swcaption[This is my short caption]{This is my extended caption that will use more than one row and its height will be automatically measured to be used for figure height adjustment}{\label{fig:A1}}{}
  \includegraphics[height=\swheight]{example-image-a}
  \makeswcap
\end{sidewaysfigure}

\clearpage
\subsection{Second example with caption below\ldots Plus text above}
\lipsum[1-2]

{\color{red}Here comes the Sidewaysfigure~\ref{fig:A2} with the caption below the figure and some text above:}

\begin{sidewaysfigure}
  \swcaption[This is my short caption]{This is my extended caption that will use more than one row and its height will be automatically measured to be used for figure height adjustment}{\label{fig:A2}}{Here is a text that will be added in this last sideways figure below the caption and the figure. Here is a text that will be added in this last sideways figure below the caption and the figure.}
  \makeswtext
  \includegraphics[height=\swheight]{example-image-b}
  \makeswcap
\end{sidewaysfigure}

\clearpage
\section{Second example with caption above}
\lipsum[1-2]

{\color{red}Here comes the Sidewaysfigure~\ref{fig:B1} with the caption above the figure:}

\begin{sidewaysfigure}
  \swcaption[This is my short caption]{This is my extended caption that will use more than one row and its height will be automatically measured to be used for figure height adjustment}{\label{fig:B1}}{}
  \makeswcap
  \includegraphics[height=\swheight]{example-image-b}
\end{sidewaysfigure}
\clearpage

\subsection{Second example with caption above\ldots Plus text}
\lipsum[1-2]

{\color{red}Here comes the Sidewaysfigure~\ref{fig:B2} with the caption above the figure and some text below}

\begin{sidewaysfigure}
  \swcaption[This is my short caption]{This is my extended caption that will use more than one row and its height will be automatically measured to be used for figure height adjustment}{\label{fig:B2}}{\vspace*{20pt}Here is a text that will be added in this last sideways figure below the caption and the figure}
\makeswcap
  \includegraphics[height=\swheight]{example-image-b}
\makeswtext
\end{sidewaysfigure}



\end{document}