NuWa DetDesc

Notes from David on setting up the 2-1-3 configution via DetDesc XML and generation scripts.

• https://wiki.bnl.gov/dayabay-private/index.php?title=Configuring_2-1-3
• http://dayabay.ihep.ac.cn/tracs/dybsvn/ticket/1085
• http://dayabay.ihep.ac.cn/tracs/dybsvn/changeset/18806