Class LineDissolver


  • public class LineDissolver
    extends java.lang.Object
    Dissolves the linear components from a collection of Geometrys into a set of maximal-length Linestrings in which every unique segment appears once only. The output linestrings run between node vertices of the input, which are vertices which have either degree 1, or degree 3 or greater.

    Use cases for dissolving linear components include generalization (in particular, simplifying polygonal coverages), and visualization (in particular, avoiding symbology conflicts when depicting shared polygon boundaries).

    This class does not node the input lines. If there are line segments crossing in the input, they will still cross in the output.

    • Constructor Detail

      • LineDissolver

        public LineDissolver()
    • Method Detail

      • dissolve

        public static Geometry dissolve​(Geometry g)
        Dissolves the linear components in a geometry.
        Parameters:
        g - the geometry to dissolve
        Returns:
        the dissolved lines
      • add

        public void add​(Geometry geometry)
        Adds a Geometry to be dissolved. Any number of geometries may be added by calling this method multiple times. Any type of Geometry may be added. The constituent linework will be extracted to be dissolved.
        Parameters:
        geometry - geometry to be line-merged
      • add

        public void add​(java.util.Collection geometries)
        Adds a collection of Geometries to be processed. May be called multiple times. Any dimension of Geometry may be added; the constituent linework will be extracted.
        Parameters:
        geometries - the geometries to be line-merged
      • add

        private void add​(LineString lineString)
      • getResult

        public Geometry getResult()
        Gets the dissolved result as a MultiLineString.
        Returns:
        the dissolved lines
      • computeResult

        private void computeResult()
      • process

        private void process​(HalfEdge e)
      • buildLines

        private void buildLines()
        For each edge in stack (which must originate at a node) extracts the line it initiates.
      • updateRingStartEdge

        private void updateRingStartEdge​(DissolveHalfEdge e)
        Updates the tracked ringStartEdge if the given edge has a lower origin (using the standard Coordinate ordering). Identifying the lowest starting node meets two goals:
        • It ensures that isolated input rings are created using the original node and orientation
        • For isolated rings formed from multiple input linestrings, it provides a canonical node and orientation for the output (rather than essentially random, and thus hard to test).
        Parameters:
        e -
      • buildLine

        private void buildLine​(HalfEdge eStart)
        Builds a line starting from the given edge. The start edge origin is a node (valence = 1 or >= 3), unless it is part of a pure ring. A pure ring has no other incident lines. In this case the start edge may occur anywhere on the ring. The line is built up to the next node encountered, or until the start edge is re-encountered (which happens if the edges form a ring).
        Parameters:
        eStart -
      • buildRing

        private void buildRing​(HalfEdge eStartRing)
      • stackEdges

        private void stackEdges​(HalfEdge node)
        Adds edges around this node to the stack.
        Parameters:
        node -