Allows Apache SIS to use Proj.4 for now (GDAL later) through Java Native Interface (JNI). This feature is provided in a separated module sis-gdal. It is aimed mostly to people who need a map projection not yet defined in Apache SIS, or who need to reproduce the exact same numerical results than Proj.4. Note that Proj.4 do not provide information on coordinate operation accuracy or domain of validity.
CRS backed by Proj.4 can be created by using a definition string like "Proj4::+init=epsg:3395 +over". Warning: despite the "epsg" word, coordinate reference systems created by "+init=epsg:" syntax in Proj.4 are not necessarily compliant with EPSG definitions. In particular, the axis order is often different. Units of measurement may also differ.