Class BufferOp


  • public class BufferOp
    extends Object
    Computes the buffer of a geometry, for both positive and negative buffer distances.

    In GIS, the positive (or negative) buffer of a geometry is defined as the Minkowski sum (or difference) of the geometry with a circle of radius equal to the absolute value of the buffer distance. In the CAD/CAM world buffers are known as offset curves. In morphological analysis the operation of positive and negative buffering is referred to as erosion and dilation

    The buffer operation always returns a polygonal result. The negative or zero-distance buffer of lines and points is always an empty Polygon.

    Since true buffer curves may contain circular arcs, computed buffer polygons are only approximations to the true geometry. The user can control the accuracy of the approximation by specifying the number of linear segments used to approximate arcs. This is specified via BufferParameters.setQuadrantSegments(int) or setQuadrantSegments(int).

    The end cap style of a linear buffer may be specified. The following end cap styles are supported:

    The join style of the corners in a buffer may be specified. The following join styles are supported:

    The buffer algorithm may perform simplification on the input to increase performance. The simplification is performed a way that always increases the buffer area (so that the simplified input covers the original input). The degree of simplification can be specified, with a default used otherwise. Note that if the buffer distance is zero then so is the computed simplify tolerance, no matter what the simplify factor.

    Buffer results are always valid geometry. Given this, computing a zero-width buffer of an invalid polygonal geometry is an effective way to "validify" the geometry. Note however that in the case of self-intersecting "bow-tie" geometries, only the largest enclosed area will be retained.

    Version:
    1.7
    • Field Detail

      • CAP_ROUND

        public static final int CAP_ROUND
        Deprecated.
        use BufferParameters
        Specifies a round line buffer end cap style.
        See Also:
        Constant Field Values
      • CAP_BUTT

        public static final int CAP_BUTT
        Deprecated.
        use BufferParameters
        Specifies a butt (or flat) line buffer end cap style.
        See Also:
        Constant Field Values
      • CAP_FLAT

        public static final int CAP_FLAT
        Deprecated.
        use BufferParameters
        Specifies a butt (or flat) line buffer end cap style.
        See Also:
        Constant Field Values
      • CAP_SQUARE

        public static final int CAP_SQUARE
        Deprecated.
        use BufferParameters
        Specifies a square line buffer end cap style.
        See Also:
        Constant Field Values
    • Constructor Detail

      • BufferOp

        public BufferOp​(Geometry g)
        Initializes a buffer computation for the given geometry
        Parameters:
        g - the geometry to buffer
      • BufferOp

        public BufferOp​(Geometry g,
                        BufferParameters bufParams)
        Initializes a buffer computation for the given geometry with the given set of parameters
        Parameters:
        g - the geometry to buffer
        bufParams - the buffer parameters to use
    • Method Detail

      • bufferOp

        public static Geometry bufferOp​(Geometry g,
                                        double distance)
        Computes the buffer of a geometry for a given buffer distance.
        Parameters:
        g - the geometry to buffer
        distance - the buffer distance
        Returns:
        the buffer of the input geometry
      • bufferOp

        public static Geometry bufferOp​(Geometry g,
                                        double distance,
                                        BufferParameters params)
        Computes the buffer for a geometry for a given buffer distance and accuracy of approximation.
        Parameters:
        g - the geometry to buffer
        distance - the buffer distance
        params - the buffer parameters to use
        Returns:
        the buffer of the input geometry
      • bufferOp

        public static Geometry bufferOp​(Geometry g,
                                        double distance,
                                        int quadrantSegments)
        Computes the buffer for a geometry for a given buffer distance and accuracy of approximation.
        Parameters:
        g - the geometry to buffer
        distance - the buffer distance
        quadrantSegments - the number of segments used to approximate a quarter circle
        Returns:
        the buffer of the input geometry
      • bufferOp

        public static Geometry bufferOp​(Geometry g,
                                        double distance,
                                        int quadrantSegments,
                                        int endCapStyle)
        Computes the buffer for a geometry for a given buffer distance and accuracy of approximation.
        Parameters:
        g - the geometry to buffer
        distance - the buffer distance
        quadrantSegments - the number of segments used to approximate a quarter circle
        endCapStyle - the end cap style to use
        Returns:
        the buffer of the input geometry
      • bufferByZero

        public static Geometry bufferByZero​(Geometry geom,
                                            boolean isBothOrientations)
        Buffers a geometry with distance zero. The result can be computed using the maximum-signed-area orientation, or by combining both orientations.

        This can be used to fix an invalid polygonal geometry to be valid (i.e. with no self-intersections). For some uses (e.g. fixing the result of a simplification) a better result is produced by using only the max-area orientation. Other uses (e.g. fixing geometry) require both orientations to be used.

        This function is for INTERNAL use only.

        Parameters:
        geom - the polygonal geometry to buffer by zero
        isBothOrientations - true if both orientations of input rings should be used
        Returns:
        the buffered polygonal geometry
      • setQuadrantSegments

        public void setQuadrantSegments​(int quadrantSegments)
        Sets the number of line segments in a quarter-circle used to approximate angle fillets for round end caps and joins.
        Parameters:
        quadrantSegments - the number of segments in a fillet for a quadrant
      • getResultGeometry

        public Geometry getResultGeometry​(double distance)
        Returns the buffer computed for a geometry for a given buffer distance.
        Parameters:
        distance - the buffer distance
        Returns:
        the buffer of the input geometry