Class GeometryPrecisionReducer


  • public class GeometryPrecisionReducer
    extends java.lang.Object
    Reduces the precision of a Geometry according to the supplied PrecisionModel, ensuring that the result is valid (unless specified otherwise).

    By default the geometry precision model is not changed. This can be overridden by using setChangePrecisionModel(boolean).

    Topological Precision Reduction

    The default mode of operation ensures the reduced result is topologically valid (i.e. Geometry.isValid() is true). To ensure this polygonal geometry is reduced in a topologically valid fashion (technically, by using snap-rounding). Note that this may change polygonal geometry structure (e.g. two polygons separated by a distance below the specified precision will be merged into a single polygon). Duplicate vertices are removed. This mode is invoked by the static method reduce(Geometry, PrecisionModel).

    Normally, collapsed linear components (e.g. lines collapsing to a point) are not included in the result. This behavior can be changed by setting setRemoveCollapsedComponents(boolean) to false, or by using the static method reduceKeepCollapsed(Geometry, PrecisionModel).

    In general input must be valid geometry, or an IllegalArgumentException will be thrown. However if the invalidity is "mild" or very small then it may be eliminated by precision reduction.

    Pointwise Precision Reduction

    Alternatively, geometry can be reduced pointwise by using setPointwise(boolean). Linear and point geometry are always reduced pointwise (i.e. without further change to topology or structure), since this does not change validity. Invalid inputs are allowed. Duplicate vertices are preserved. Collapsed components are always included in the result. The result geometry may be invalid.

    This mode is invoked by the static method reducePointwise(Geometry, PrecisionModel).

    Version:
    1.12
    • Constructor Detail

      • GeometryPrecisionReducer

        public GeometryPrecisionReducer​(PrecisionModel pm)
    • Method Detail

      • reduce

        public static Geometry reduce​(Geometry g,
                                      PrecisionModel precModel)
        Reduces precision of a geometry, ensuring output geometry is valid. Collapsed linear and polygonal components are removed. Duplicate vertices are removed. The geometry precision model is not changed.

        Invalid input geometry may cause an error, unless the invalidity is below the scale of the precision reduction.

        Parameters:
        g - the geometry to reduce
        precModel - the precision model to use
        Returns:
        the reduced geometry
        Throws:
        java.lang.IllegalArgumentException - if the reduction fails due to invalid input geometry
      • reduceKeepCollapsed

        public static Geometry reduceKeepCollapsed​(Geometry geom,
                                                   PrecisionModel pm)
        Reduces precision of a geometry, ensuring output polygonal geometry is valid, and preserving collapsed linear elements. Duplicate vertices are removed. The geometry precision model is not changed.

        Invalid input geometry may cause an error, unless the invalidity is below the scale of the precision reduction.

        Parameters:
        g - the geometry to reduce
        precModel - the precision model to use
        Returns:
        the reduced geometry
        Throws:
        java.lang.IllegalArgumentException - if the reduction fails due to invalid input geometry
      • reducePointwise

        public static Geometry reducePointwise​(Geometry g,
                                               PrecisionModel precModel)
        Reduce precision of a geometry in a pointwise way. All input geometry elements are preserved in the output, including invalid polygons and collapsed polygons and linestrings. The output may not be valid, due to collapse or self-intersection. Duplicate vertices are not removed. The geometry precision model is not changed.

        Invalid input geometry is allowed.

        Parameters:
        g - the geometry to reduce
        precModel - the precision model to use
        Returns:
        the reduced geometry
      • setRemoveCollapsedComponents

        public void setRemoveCollapsedComponents​(boolean removeCollapsed)
        Sets whether the reduction will result in collapsed components being removed completely, or simply being collapsed to an (invalid) Geometry of the same type. The default is to remove collapsed components.
        Parameters:
        removeCollapsed - if true collapsed components will be removed
      • setChangePrecisionModel

        public void setChangePrecisionModel​(boolean changePrecisionModel)
        Sets whether the PrecisionModel of the new reduced Geometry will be changed to be the PrecisionModel supplied to specify the precision reduction.

        The default is to not change the precision model

        Parameters:
        changePrecisionModel - if true the precision model of the created Geometry will be the the precisionModel supplied in the constructor.
      • setPointwise

        public void setPointwise​(boolean isPointwise)
        Sets whether the precision reduction will be done in pointwise fashion only. Pointwise precision reduction reduces the precision of the individual coordinates only, but does not attempt to recreate valid topology. This is only relevant for geometries containing polygonal components.
        Parameters:
        isPointwise - if reduction should be done pointwise only
      • reduce

        public Geometry reduce​(Geometry geom)
        Reduces the precision of a geometry, according to the specified strategy of this reducer.
        Parameters:
        geom - the geometry to reduce
        Returns:
        the precision-reduced geometry
        Throws:
        java.lang.IllegalArgumentException - if the reduction fails due to invalid input geometry is invalid