Create a new compact detector description XML file by copying and modifying an existing one or authoring a new file. Checkout the LCDetectors project for the complete set of public compact detector descriptions. Otherwise, download them individually from http://www.lcsim.org/detectors.
Decide on a unique name for this detector which will be denoted as DETECTOR_NAME in these instructions.
Create a directory called DETECTOR_NAME.
Copy the compact.xml file to the directory.
In the new compact file, change the name field to your new detector name.
<info name="DETECTOR_NAME"/>
It is very important to change this tag. Otherwise, the detector conditions system will not recognize your new detector model.
Create a new file called detector.properties in the detector's directory, which should contain the following line.
name: DETECTOR_NAME
Make all the changes required to this compact description. Once you have a working compact description, it is advisable to permanently freeze this description and not make any more changes. If you want to change it later on, the best approach is to redo these instructions and create a new compact description and unique name.
Regenerate the LCDD file for your detector so events can be simulated.