Including GRSD a global radius-based surface descriptor

GRSD is developed by Zoltan-Marton, this was a old patch as part of his branch being included into the trunk.
I am not sure what confuses you there. Static functions is not something PCL-specific... just have a look at some article (like [this](http://www.tutorialspoint.com/cplusplus/cpp_static_members.htm)) to give yourself a refresher on the topic.