Before building jeo a few upstream libraries must first be built and installed in the local maven repository.
Build the jeo branch of the proj4j repository.
git clone https://github.com/jdeolive/proj4j.git
cd proj4j
git checkout jeo
mvn install
jeo requires the protoc program. On OSX, it is best to build it from source with configure && make && sudo make install.
git clone https://github.com/jdeolive/jeo
cd jeo
mvn install