Union or intersection of envelopes in different CRS

Before to compute the union or intersection of two or more envelopes (bounding boxes), all envelopes must be transformed to the same Coordinate Reference System (CRS). But the choice of a common CRS is not easy. We must verify that all envelopes are inside the domain of validity of the common CRS, which may require to choose a common CRS different than the CRS of all envelopes. Apache SIS can handle this task automatically.

Direct dependencies

Maven coordinates	Module info
`org.apache.sis.storage:sis-referencing`	`org.apache.sis.referencing`

Code example

Note that all geographic coordinates below express latitude before longitude.

import org.opengis.geometry.Envelope;
import org.opengis.referencing.crs.CoordinateReferenceSystem;
import org.opengis.referencing.operation.TransformException;
import org.opengis.util.FactoryException;
import org.apache.sis.referencing.CommonCRS;
import org.apache.sis.geometry.Envelopes;
import org.apache.sis.geometry.Envelope2D;

public class UnionOfEnvelopes {
    /**
     * Demo entry point.
     *
     * @param  args  ignored.
     * @throws FactoryException   if an error occurred while creating a Coordinate Reference System (CRS).
     * @throws TransformException if an error occurred while transforming coordinates to the target CRS.
     */
    public static void main(String[] args) throws FactoryException, TransformException {
        CoordinateReferenceSystem crs1 = CommonCRS.WGS84.universal(40, 10);     // 40°N 10°E
        CoordinateReferenceSystem crs2 = CommonCRS.WGS84.universal(40, 20);     // 40°N 20°E

        Envelope2D bbox1 = new Envelope2D(crs1, 500_000, 400_000, 100_000, 100_000);
        Envelope2D bbox2 = new Envelope2D(crs2, 400_000, 500_000, 100_000, 100_000);
        Envelope   union = Envelopes.union(bbox1, bbox2);

        System.out.println("First CRS:    " + crs1.getName());
        System.out.println("Second CRS:   " + crs2.getName());
        System.out.println("Selected CRS: " + union.getCoordinateReferenceSystem().getName());
        System.out.println("Union result: " + union);
    }
}

Output

First CRS:    EPSG:WGS 84 / UTM zone 32N
Second CRS:   EPSG:WGS 84 / UTM zone 34N
Selected CRS: EPSG:WGS 84
Union result: BOX(3.6184285185271796 9, 5.428225419697392 21)