How to make sweave copy generated graphics to a subfolder?

I would love to use some shell script based pdfcrop on all the graphics.pdf created from my Sweave report. Hence i'd be nice if all the graphics were stored to a subfolder instead of being dropped where all the latex stuff like .aux .log files (and so on) is located. If I just had to use the crop script on ALL files in a particular directory it would be much easier.

Here's my Sweave chunk:

\begin{figure}[htbp]
  \begin{center}
  <<fig=true,echo=false>>=
  print(mygraph)
  @
\caption{my graph}
\end{center}
\end{figure}

If I run the sweave code mygraph.pdf is stored in the same directory as the report.tex file itself.

Is there a way to store this file in an existing subfolder like /graphics ?

Solution

Insert this:

\SweaveOpts{prefix.string=foo/bar}

into your Sweave source file, preferably up the top in the preamble. The above line is taken from the Sweave FAQ, and indicates that the created figures will be stored in the subdirectory (of the directory where the Sweave source is) foo, and each image filename will begin with bar. This, and a whole lot more is discussed in the Sweave FAQ.