Support the Military Grid Reference System (MGRS). The MGRS is the geocoordinate standard used by NATO militaries for locating points on the earth. It is based on the Universal Transverse Mercator (UTM) and the Universal Polar Stereographic (UPS) projections. Despite its name, MGRS is used not only for military purposes; it is used also for organizing Earth Observation data in directory trees for example.
MGRS can be used as an alternative to GeoHashCoder already available since Apache SIS 0.1. A MGRS advantage is that it uses rectangular coordinates in metres instead than degrees, and that it provides a way to divide the Earth in grid cells of the same size (except those that are on the border between two zones).