overpic absolute positioning for local figure only

The options for absolute and relative positioning are evaluated at run time only. But this can be made more flexible.

The following example defines keys abs, percent, permille, rel=<number> that can be used in the optional argument of \begin{overpic}[...]. The latter option allows the specification of a different divisor than 100 (percent) or 1000 (permille). The number must be a positive integer.

The example is based on package overpic's examples overpic-abs.pdf and overpic-rel.pdf; golfer.eps comes from the examples of Ghostscript.

\documentclass{article}
\usepackage{overpic}

\makeatletter
\newcommand\OVP@calc@tmp{%
  \setlength{\unitlength}{\@tempdima}%
  \divide\@tempcnta by \unitlength
  \divide\@tempcntb by \unitlength
  \ifnum\count@=\z@\count@=10\fi
}%
\let\OVP@calc@abs=\OVP@calc@tmp

\renewcommand\OVP@calc@tmp{%  
  \ifnum\@tempcnta>\@tempcntb
    \divide\@tempcnta by \OVP@scale
    \setlength\unitlength{\@tempcnta sp}% 
    \@tempcnta=\OVP@scale
    \divide\@tempcntb by \unitlength
  \else
    \divide\@tempcntb by \OVP@scale
    \setlength\unitlength{\@tempcntb sp}%  
    \@tempcntb=\OVP@scale
    \divide\@tempcnta by \unitlength
  \fi
  \ifnum\count@=\z@
    \count@=\OVP@scale\divide\count@ by 10 %
  \fi
}%
\let\OVP@calc@rel\OVP@calc@tmp

\define@key{Gin}{abs}[]{%
  \let\OVP@calc\OVP@calc@abs
}
\define@key{Gin}{percent}[]{%
  \setkeys{Gin}{rel=100}%
}
\define@key{Gin}{permille}[]{%
  \setkeys{Gin}{rel=\@m}%
}
\define@key{Gin}{rel}{%
  \renewcommand{\OVP@scale}{#1}%
  \ifnum\OVP@scale>\z@
    \let\OVP@calc\OVP@calc@rel
  \else
    \PackageError{overpic}{Invalid number for option `rel'}\@ehc
  \fi
}
\makeatother

\begin{document}
  \begin{overpic}[
    scale=.25,
  ]{golfer.eps}
    \put(5,45){\huge \LaTeX}
    \put(55,10){\includegraphics[scale=.07]{golfer.eps}}
  \end{overpic}

  \begin{overpic}[
    scale=.25,
    rel=20,
  ]{golfer.eps}
    \put(1,9){\huge \LaTeX}
    \put(11,2){\includegraphics[scale=.07]{golfer.eps}}
  \end{overpic}

  \begin{overpic}[
    scale=.25,
    unit=1mm,
    abs,
  ]{golfer.eps}
    \put(3,28){\huge \LaTeX}
    \put(34,5){\includegraphics[scale=.07]{golfer.eps}}
  \end{overpic}
\end{document}