Proj4J

To include the core Proj4J library in a Gradle project, add the following implementation dependency:

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

To include the core Proj4J library in a Maven project, add the following dependency. Note that as of version 1.2.2, the core library does not include EPSG licensed files, so you may need to include the proj4j-epsg dependency as well for full functionality.

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

To include the EPSG dataset module in a Gradle project, add the following implementation dependency:

    implementation 'org.locationtech.proj4j:proj4j-epsg:{latest version}'

The proj4j-epsg module distributes a portion of the EPSG dataset. This artifact is released under the EPSG database distribution license. Use this dependency to ensure Proj4J can operate with standard EPSG definitions.

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

To include the GeoAPI wrapper module in a Gradle project, add the following implementation dependency:

    implementation 'org.locationtech.proj4j:proj4j-geoapi:{latest version}'

The proj4j-geoapi module provides wrappers to use Proj4J behind GeoAPI interfaces, which are Java interfaces derived from OGC/ISO standards.

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

If your application uses the GeoAPI (OpenGIS) standard, TransformWrapper2D provides a bridge between PROJ4J's CoordinateTransform and the MathTransform2D interface. It allows you to perform 2D coordinate transformations using standard GeoAPI methods.

Key characteristics:

• Dimensions: Always operates on 2D coordinates (Source: 2, Target: 2).
• Precision: Supports transformations using double[], float[], or Point2D objects.
• Shape Support: Can transform java.awt.Shape objects by transforming their control points.
• Inverse: Supports retrieving the inverse transformation via .inverse().

To perform a reverse transformation (from target CRS back to source CRS), call the .inverse() method. The result is cached after the first call to improve performance.

MathTransform2D inverseTransform = mathTransform.inverse();

The TransformWrapper2D class implements several transform methods to handle different data formats. Note that when using the same array for both source and destination (srcPts == dstPts), the implementation handles overlapping memory by creating a temporary copy if necessary to prevent data corruption.

// Transforming a single Point2D
Point2D srcPt = new Point2D.Double(x, y);
Point2D dstPt = new Point2D.Double();
mathTransform.transform(srcPt, dstPt);

// Transforming arrays of coordinates (double precision)
// srcOff and dstOff are the starting indices in the arrays
// numPts is the number of 2D coordinate pairs to transform
mathTransform.transform(srcPts, srcOff, dstPts, dstOff, numPts);

// Transforming arrays of coordinates (float precision)
mathTransform.transform(srcPts, srcOff, dstPts, dstOff, numPts);

You can transform a java.awt.Shape (like a Path2D) into a new shape in the target coordinate system. The implementation iterates through the shape's path segments (MOVETO, LINETO, QUADTO, CUBICTO) and transforms the control points.

Warning: This is a simple implementation that transforms control points; it does not check if straight lines should be converted to curves due to the transformation.

// Returns a new Shape representing the transformed geometry
Shape transformedShape = mathTransform.createTransformedShape(originalShape);