Change figure numbering for appendix

Question

I want to "reset" the figure counting in my document when the appendix starts, and follow a different pattern than 1, 2, 3... Specifically, I want figures in the appendix to start with A.1, A.2 onward, instead of continuing on from the main document. How can I do this?

\documentclass[twoside]{article}

\usepackage{graphicx,dblfloatfix}


\usepackage{titlesec}% Allows customization of titles
\titleformat{\section}[block]{\large\scshape\centering{\Roman{section}.}}{}{1em}{} % Change the look of the section titles 

\begin{document}

\section{Introduction}
\subsection{Problem description}
Blah blah
\begin{figure}[!htb]
    \centering 
    \includegraphics{decon}
    \caption{Call this figure 1.}
\label{fig1} 
\end{figure}
\appendix
\section{Figures}

\begin{figure}[!htb]
    \centering 
    \includegraphics{decon}
    \caption{Call this figure A.1.}
\label{figa1} 
\end{figure}

\begin{figure}[!htb]
    \centering 
    \includegraphics{decon}
    \caption{Call this figure A.2.}
\label{figa2} 
\end{figure}

\end{document}

Answer 1

Redefine \thefigure when your appendices start, and set the figure counter to zero at the beginning of each appendix.

\documentclass{article}
\begin{document}
\begin{figure}
\centering\rule{1cm}{1cm}
\caption{This is a figure}
\end{figure}
\appendix
\renewcommand\thefigure{\thesection.\arabic{figure}}    
\section{A nice appendix}
\setcounter{figure}{0}    
\begin{figure}
\centering\rule{1cm}{1cm}
\caption{This is a figure in appendix A}
\end{figure}
\end{document}

Answer 2

You can use the chngcntr package which includes the command \counterwithin.

Using this as \counterwithin{figure}{section} changes the figure numbering from that point on so that the section number is included and resets the numbering of figures at the beginning each subsequent section. An example is:

\documentclass{article}

\usepackage{chngcntr}

\begin{document}

\section{Introduction}

\subsection{Problem description}

\begin{figure}[htp]
  \centering Figure
  \caption{Call this figure 1.}
  \label{fig1}
\end{figure}

\appendix
\counterwithin{figure}{section}

\section{Figures}

\begin{figure}[htp]
  \centering Figure
  \caption{Call this figure A.1.}
  \label{figa1}
\end{figure}

\begin{figure}[htp]
  \centering Figure
  \caption{Call this figure A.2.}
  \label{figa2}
\end{figure}

\end{document}

Answer 3

A simple way to prepend an A to your appendix figures and to have the counter reset is to paste the following two lines before your first figure of the appendix.

\renewcommand{\thefigure}{A\arabic{figure}}

\setcounter{figure}{0}

as illustrated here.

Answer 4

I added - hbAppendixPrefix to change prefix easily - equation numbering, too

\newcommand{\hbAppendixPrefix}{A}
%
\renewcommand{\thefigure}{\hbAppendixPrefix\arabic{figure}}
\setcounter{figure}{0}
\renewcommand{\thetable}{\hbAppendixPrefix\arabic{table}} 
\setcounter{table}{0}
\renewcommand{\theequation}{\hbAppendixPrefix\arabic{equation}} 
\setcounter{equation}{0}

Answer 5

This is the solution for everything which manages both figures and tables in appendix

\appendix
\appendixpage
\addappheadtotoc
\counterwithin{figure}{section}
\counterwithin{table}{section}

Answer 6

I can't comment yet due to low rep but I want to add a note that expands on the answer by @ian-thompson

If you want to add a prefix to all figures and tables in the appendix regardless of which section of the appendix it's in, you can use the code below. Ian's answer generates Figure A.1, A.2 etc in the first section of an appendix but then Figure B.1, B.2 in the next section. If you want static prefix, we remove "\thesection" from the renewcommand line.

\documentclass{article}
\begin{document}
\begin{figure}
\centering\rule{1cm}{1cm}
\caption{This is a figure}
\end{figure}
\appendix


% Change figure labelling
\renewcommand\thefigure{PrefixTextHere.\arabic{figure}}    
\setcounter{figure}{0}  

% Change table labelling
\renewcommand\thetable{PrefixTextHere.\arabic{figure}}    
\setcounter{table}{0}    

\begin{figure}
\centering\rule{1cm}{1cm}
\caption{This is a figure in appendix A}
\end{figure}
\end{document}

In relation to the OP's request the relevant lines to graft into the above would be:

\renewcommand\thefigure{A.\arabic{figure}}    
\renewcommand\thefigure{A.\arabic{figure}}   

Answer 7

A solution that doesn't break hyperref and doesn't require additional packages is as follows:

\documentclass{article}

\usepackage{hyperref}

\begin{document}

Text.

\begin{figure}
  \centering Figure.
  \caption{Main text figure.}
  \label{fig:one}
\end{figure}

This links to a figure in the main text: Fig.~\ref{fig:one}. But this links to a figure in the appendix: Fig.~\ref{fig:Aone}.

\cleardoublepage % just to show that the cross-references go to different places

\appendix

\counterwithin*{figure}{part}

\stepcounter{part}

\renewcommand{\thefigure}{A.\arabic{figure}}

This is the Appendix.

\begin{figure}
  \centering Appendix Figure.
  \caption{A figure in the Appendix.}
  \label{fig:Aone}
\end{figure}


\end{document}