Proj4J is a Java library for converting coordinates between different geospatial coordinate reference systems. It is designed to be compatible with proj.4 parameters and derives some of its implementation from the proj.4 sources.

Proj4J is a project in the LocationTech working group of the Eclipse Foundation.

Proj4J artifacts are available on maven central.

To include Proj4J in a Maven project, add a dependency block like the following:

<properties>
    <proj4j.version><latest version></proj4j.version>
</properties>
<dependency>
    <groupId>org.locationtech.proj4j</groupId>
    <artifactId>proj4j</artifactId>
    <version>${proj4j.version}</version>
</dependency>

where <latest version> refers to the version indicated by the badge above.

To include Proj4J in a Gradle project, add a dependency block like the following:

dependencies {
    implementation 'org.locationtech.proj4j:proj4j:<latest version>'
}

where <latest version> refers to the version indicated by the badge above.

The following examples give a quick intro on how to use Proj4J in common use cases.

CRSFactory crsFactory = new CRSFactory();
CoordinateReferenceSystem WGS84 = crsFactory.createFromName("epsg:4326");
CoordinateReferenceSystem UTM = crsFactory.createFromName("epsg:25833");

CRSFactory crsFactory = new CRSFactory();
CoordinateReferenceSystem WGS84 = crsFactory.createFromParameters("WGS84",
    "+proj=longlat +datum=WGS84 +no_defs");
CoordinateReferenceSystem UTM = crsFactory.createFromParameters("UTM",
    "+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs");

CoordinateTransformFactory ctFactory = new CoordinateTransformFactory();
CoordinateTransform wgsToUtm = ctFactory.createTransform(WGS84, UTM);
// `result` is an output parameter to `transform()`
ProjCoordinate result = new ProjCoordinate();
wgsToUtm.transform(new ProjCoordinate(lon, lat), result);

mvn clean install

mvn -Dmaven.test.skip=true -Pcentral clean package deploy

If you are interested in contributing to Proj4J please read the Contributing Guide.