Figures wider than \textwidth in document with different inside and outside margins

Question

I am using the ClassicThesis template. Infrequently, I want to include figures wider than the \textwidth or \linewidth. My current workaround is:

\begin{figure}
\centering
\hspace*{-2cm} 
\captionsetup{margin={-0pt,-2cm}}
\makebox[\textwidth][c]{\includegraphics[width=1.3\textwidth]{images/MyImage.pdf}}
 \caption{Here goes my caption}
  \label{fig:MyImage} 
\end{figure}

The problem is: I have to adjust the -2cm to +2cm depending if the pdf output is a 'left' or a 'right' side. This is because ClassicThesis uses a substantially larger outside margin. So, I would have to go through my entire document (once it is completed) and then eyeball whether it is a 'left' page or not and then adjust the -2cm or +2cm accordingly.

Is there a more elegant way of doing this?

And another question building on that, would this more elegant solution also work for my longtables? Currently, I use this:

{\small 
\setlength\LTleft{-40pt}
\setlength\LTright{-40pt}
\setlength\LTcapwidth{\linewidth}
\begin{longtable}{p{1.5cm}p{14 cm}}
\caption{My Caption} \\
\toprule
Column A & Column B  \\
\hline
\endfirsthead
\multicolumn{2}{@{}l}{\ldots continued}\\\hline
Column A & Column B \\\hline
\endhead % all the lines above this will be repeated on every page
\hline
\multicolumn{2}{r@{}}{continued \ldots}\\
\endfoot
\hline
\endlastfoot
Entry Column A & Entry Column B \
\end{longtable}%
\label{tab:MyTab}%
}

Answer 1

This creates a new environment, widefigure. It doesn't actually center the figure on the page, but figures on even and odd pages will line up.

You need to run it twice, since iffoddpage uses the aux file.

It appears one cannot change \LTleft or \LTright in the middle of a longtable.

\documentclass{book}
\usepackage{ClassicThesis}
\usepackage{ifoddpage}% \value{page} is not reliable
\newlength{\LRshift}
\setlength{\LRshift}{\dimexpr 0.5\oddsidemargin-0.5\evensidemargin}
\newsavebox{\widefigurebox}
\newenvironment{widefigure}[1][tbp]{\figure[#1]
  \begin{lrbox}{\widefigurebox}}%
{\end{lrbox}%
  \checkoddpage
  \ifoddpage \LRshift=-\LRshift \fi% local change
  \leavevmode\rlap{\hspace{\dimexpr \LRshift + 0.5\textwidth - 0.5\wd\widefigurebox}
    \usebox\widefigurebox}%
  \endfigure}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{lipsum}
\begin{document}
\begin{widefigure}
\begin{minipage}{1.3\textwidth}
\includegraphics[width=\linewidth]{example-image}
 \caption{Here goes my caption}
  \label{fig:MyImage} 
\end{minipage}%
\end{widefigure}
\lipsum[1-4]
\begin{widefigure}
\begin{minipage}{1.3\textwidth}
\includegraphics[width=\linewidth]{example-image}
 \caption{Here goes my caption}
  \label{fig:MyImage} 
\end{minipage}%
\end{widefigure}
\end{document}

Answer 2

With use of the changepage package:

\documentclass{article}
\usepackage{graphicx}
\usepackage{booktabs, longtable}           
\usepackage[strict]{changepage} % <---
%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\usepackage{lipsum}
\begin{document}
\section{Introduction}
\lipsum[1][1-4]
    \begin{figure}[ht]
\begin{adjustwidth}{}{\dimexpr-\marginparwidth-\marginparsep}
\includegraphics[width=\linewidth]{example-image-duck}
\caption{Image wich width is equal to \texttt{text width + marginparwidth + marginparsep}}
\end{adjustwidth}
    \end{figure}
\lipsum[1][5-8]
\begin{adjustwidth}{}{\dimexpr-\marginparwidth-\marginparsep}
\begin{longtable}{*{2}{p{\dimexpr0.5\linewidth-2\tabcolsep}}}
\caption{Long table wider than text width}\
    \toprule
\lipsum[66] &   \lipsum[66] \
    \midrule
\lipsum[66] &   \lipsum[66] \
    \bottomrule
\end{longtable}
\end{adjustwidth}
\lipsum[2]
\end{document}

Addedndum: Above proposed solution doesn't work well in two side document. In such cases a possible work around can be manualy split long table into two (and more, if necessary) parts, and each enclose in table float as is done in MWE below:

\documentclass[twoside]{article}
\usepackage{graphicx}
\usepackage{booktabs, longtable}
\usepackage[strict]{changepage} % <---
\usepackage[skip=1ex]{caption}
%---------------- Show page layout. Don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\usepackage{lipsum}% For dummy text. Don't use in a real document
\begin{document}
\section{Introduction}
\lipsum[1][1-2]
    \begin{figure}[ht]
\begin{adjustwidth}{}{\dimexpr-\marginparwidth-\marginparsep}
\includegraphics[width=\linewidth, height=0.5\linewidth]{example-image-duck}
\caption{Wide image}
\end{adjustwidth}
    \end{figure}
\lipsum[1][3-5]
\begin{table}[b]    % &lt;--- observe [b]

\begin{adjustwidth}{}{\dimexpr-\marginparwidth-\marginparsep} % <--- observe 
    \caption{Long table wider than text width}
    \label{tab:long}
\begin{tabular}{{2}{p{\dimexpr0.5\linewidth-2\tabcolsep}}}
    \toprule
\lipsum[66] &   \lipsum[66] \
    \midrule
\multicolumn{2}{r}{\footnotesize\textit{Continue on the next page}}
    \end{tabular}
\end{adjustwidth}
    \end{table}
%
    \begin{table}[t]    % <--- observe [t]
\begin{adjustwidth}{}{\dimexpr-\marginparwidth-\marginparsep} % <--- observe 
\ContinuedFloat
\caption[]{Long table wider than text width -- continued from previous page}
\begin{tabular}{{2}{p{\dimexpr0.5\linewidth-2\tabcolsep}}}
    \toprule
\lipsum[66] &   \lipsum[66] \
    \bottomrule
    \end{tabular}
\end{adjustwidth}
    \end{table}
\lipsum[2]
\end{document}

Answer 3

Sorry for being unspecific by answering as a comment, I ran out of characters to use. Now, as a full answer:

My challenge was that a long caption was still cut off according to the old \textwidth

I linked the other solution which inspired this workaround:

\documentclass[twoside]{article}
\usepackage{graphicx}
\usepackage{booktabs, longtable}
\usepackage[strict]{changepage} 
\usepackage[skip=1ex]{caption}
%---------------- Show page layout. Don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\usepackage{lipsum}% For dummy text. Don't use in a real document
\begin{figure}[ht]
\begin{adjustwidth}{}{\dimexpr-\marginparwidth-\marginparsep}
\sbox0{\includegraphics[width=\linewidth]{images/example-image-duck}}
\begin{minipage}{\wd0}
  \usebox0
  \caption{Here goes my very long caption that would usually be cut off right after reaching the width of \textwidth, but now it can be even longer and is neatly aligned with the overall text} \label{fig:IHaveToMakeSureToPutTheLabelRightInHereOtherwiseReferenesWontWork}
  \end{minipage}
\end{adjustwidth}
\end{figure}