Split “include graphics” on two pages but keep same Figure number

Question

In my MWE below, I originally had the figures on one page, but then as I added more text, it became apparent that I had to split the figures across two pages. I wanted to keep the same Figure number for both figures (Figure 1). Is the best practice to use the \renewcommand{\thefigure}{1} command? Will I have a problem if I then try to reference part A and part B Figures in the document? Thanks for your help.

Here is my code:

\documentclass[11 pt]{book}
\usepackage[draft]{pgf}
\usepackage{lipsum}
\usepackage{float}

\begin{document}
\lipsum[1-2]
\begin{figure}[H]
\centering
\begin{pgfpicture}
    \pgftext{\pgfimage[width=13cm,height=7cm]{scratch.png}}
\end{pgfpicture}
\label{fig1_ptA}
\caption{This is the first figure.}
\end{figure}
\renewcommand{\thefigure}{1}
\begin{figure}[H]
\centering
\begin{pgfpicture}
    \pgftext{\pgfimage[width=13cm,height=7cm]{scratch.png}}
\end{pgfpicture}
\label{fig1_ptB}
\caption{This is the first figure (continued).}
\end{figure}

\end{document}

Answer 1

Package caption for such cases define macro \ContinuedFloat. To the float, which is continuation of the previous one, you only need add this macro after begin{figure}:

\documentclass[11 pt]{book}
\usepackage[draft]{pgf}
\usepackage{lipsum}
%\usepackage{float} % <-- not used
\usepackage{caption}% <-- added

\begin{document}
\lipsum[1-2]
    \begin{figure}[!b]
\centering
\begin{pgfpicture}
    \pgftext{\pgfimage[width=\linewidth,height=7cm]{scratch.png}}
\end{pgfpicture}
\caption{This is the first figure.} 
\label{fig1_ptA}    % <-- had to be after caption
\end{figure}
%
\begin{figure}[!t]
\ContinuedFloat     % <--- added
\centering
\begin{pgfpicture}
    \pgftext{\pgfimage[width=\linewidth,height=7cm]{scratch.png}}
\end{pgfpicture}
\caption{This is the first figure (continued).}
\label{fig1_ptB}    % <-- had to be after caption
    \end{figure}
\lipsum[3]

See Fig.~\ref{fig1_ptA} on page \pageref{fig1_ptA} and Fig.~\ref{fig1_ptB}  on page \pageref{fig1_ptB} \dots

\end{document}