The Detector Framework module can be used to convert compact.xml files to other output formats including LCDD files for the SLIC detector simulation application.
Assuming that the entire trunk of LCSim was built successfully, then the Detector Framework jar can be executed from the command line as follows:
cd lcsim/trunk java -jar ./detector-framework/target/lcsim-detector-framework-3.1.7-bin.jar
This will show a GUI that allows you to select an input compact.xml file, a conversion format target, and the name of the output file.