You have to be able to compile OpenCPN itself - Get the info at http://opencpn.org/ocpn/developers_manual
- go to the plugin subdirectory in your OpenCPN source tree
- git clone git://github.com/bdbcat/gradar_pi.git
Build as normally:
- cd ..
- cd build
- cmake ..
- cmake --build .
The plugin code is licensed under the terms of the GPL v2 or, at your will, later.