Package org.locationtech.jts.operation.union

Class UnaryUnionOp

  • public class UnaryUnionOp
extends Object
    Unions a Collection of Geometrys or a single Geometry (which may be a GeometryCollection) together. By using this special-purpose operation over a collection of geometries it is possible to take advantage of various optimizations to improve performance. Heterogeneous GeometryCollections are fully supported.

    The result obeys the following contract:

    • Unioning a set of Polygons has the effect of merging the areas (i.e. the same effect as iteratively unioning all individual polygons together).
    • Unioning a set of LineStrings has the effect of noding and dissolving the input linework. In this context "fully noded" means that there will be an endpoint or node in the result for every endpoint or line segment crossing in the input. "Dissolved" means that any duplicate (i.e. coincident) line segments or portions of line segments will be reduced to a single line segment in the result. This is consistent with the semantics of the Geometry.union(Geometry) operation. If merged linework is required, the LineMerger class can be used.
    • Unioning a set of Points has the effect of merging all identical points (producing a set with no duplicates).
    UnaryUnion always operates on the individual components of MultiGeometries. So it is possible to use it to "clean" invalid self-intersecting MultiPolygons (although the polygon components must all still be individually valid.)
    Author:
    mbdavis

    • Constructor Detail

      • UnaryUnionOp

        public UnaryUnionOp​(Collection geoms,
                    GeometryFactory geomFact)
        Constructs a unary union operation for a Collection of Geometrys.
        Parameters:
        geoms - a collection of geometries
        geomFact - the geometry factory to use if the collection is empty

      • UnaryUnionOp

        public UnaryUnionOp​(Collection geoms)
        Constructs a unary union operation for a Collection of Geometrys, using the GeometryFactory of the input geometries.
        Parameters:
        geoms - a collection of geometries

    • Method Detail

      • union

        public static Geometry union​(Collection geoms)
        Computes the geometric union of a Collection of Geometrys.
        Parameters:
        geoms - a collection of geometries
        Returns:
        the union of the geometries, or null if the input is empty

      • union

        public static Geometry union​(Collection geoms,
                             GeometryFactory geomFact)
        Computes the geometric union of a Collection of Geometrys. If no input geometries were provided but a GeometryFactory was provided, an empty GeometryCollection is returned.
        Parameters:
        geoms - a collection of geometries
        geomFact - the geometry factory to use if the collection is empty
        Returns:
        the union of the geometries, or an empty GEOMETRYCOLLECTION

      • union

        public static Geometry union​(Geometry geom)
        Constructs a unary union operation for a Geometry (which may be a GeometryCollection).
        Parameters:
        geom - a geometry to union
        Returns:
        the union of the elements of the geometry or an empty GEOMETRYCOLLECTION

      • setUnionFunction

        public void setUnionFunction​(UnionStrategy unionFun)

      • union

        public Geometry union()
        Gets the union of the input geometries.

        The result of empty input is determined as follows:

        1. If the input is empty and a dimension can be determined (i.e. an empty geometry is present), an empty atomic geometry of that dimension is returned.
        2. If no input geometries were provided but a GeometryFactory was provided, an empty GeometryCollection is returned.
        3. Otherwise, the return value is null.
        Returns:
        a Geometry containing the union, or an empty atomic geometry, or an empty GEOMETRYCOLLECTION, or null if no GeometryFactory was provided