com.vividsolutions.jts.geom.util

Class GeometryTransformer


  • public class GeometryTransformer
extends Object
    A framework for processes which transform an input Geometry into an output Geometry, possibly changing its structure and type(s). This class is a framework for implementing subclasses which perform transformations on various different Geometry subclasses. It provides an easy way of applying specific transformations to given geometry types, while allowing unhandled types to be simply copied. Also, the framework ensures that if subcomponents change type the parent geometries types change appropriately to maintain valid structure. Subclasses will override whichever transformX methods they need to to handle particular Geometry types.

    A typically usage would be a transformation class that transforms Polygons into Polygons, LineStrings or Points, depending on the geometry of the input (For instance, a simplification operation). This class would likely need to override the #transformMultiPolygon(MultiPolygon, Geometry)transformMultiPolygon method to ensure that if input Polygons change type the result is a GeometryCollection, not a MultiPolygon.

    The default behaviour of this class is simply to recursively transform each Geometry component into an identical object by deep copying down to the level of, but not including, coordinates.

    All transformX methods may return null, to avoid creating empty or invalid geometry objects. This will be handled correctly by the transformer. transformXXX methods should always return valid geometry - if they cannot do this they should return null (for instance, it may not be possible for a transformLineString implementation to return at least two points - in this case, it should return null). The #transform(Geometry)transform method itself will always return a non-null Geometry object (but this may be empty).

    See Also:
    GeometryEditor

    • Constructor Detail

      • GeometryTransformer

        public GeometryTransformer()

    • Method Detail

      • getInputGeometry

        public Geometry getInputGeometry()
        Utility function to make input geometry available
        Returns:
        the input geometry

      • createCoordinateSequence

        protected final CoordinateSequence createCoordinateSequence(Coordinate[] coords)
        Convenience method which provides standard way of creating a CoordinateSequence
        Parameters:
        coords - the coordinate array to copy
        Returns:
        a coordinate sequence for the array

      • transformCoordinates

        protected CoordinateSequence transformCoordinates(CoordinateSequence coords,
                                                  Geometry parent)
        Transforms a CoordinateSequence. This method should always return a valid coordinate list for the desired result type. (E.g. a coordinate list for a LineString must have 0 or at least 2 points). If this is not possible, return an empty sequence - this will be pruned out.
        Parameters:
        coords - the coordinates to transform
        parent - the parent geometry
        Returns:
        the transformed coordinates

      • transformLinearRing

        protected Geometry transformLinearRing(LinearRing geom,
                                       Geometry parent)
        Transforms a LinearRing. The transformation of a LinearRing may result in a coordinate sequence which does not form a structurally valid ring (i.e. a degnerate ring of 3 or fewer points). In this case a LineString is returned. Subclasses may wish to override this method and check for this situation (e.g. a subclass may choose to eliminate degenerate linear rings)
        Parameters:
        geom - the ring to simplify
        parent - the parent geometry
        Returns:
        a LinearRing if the transformation resulted in a structurally valid ring