Package org.locationtech.jts.operation.linemerge

Class LineSequencer

java.lang.Object
org.locationtech.jts.operation.linemerge.LineSequencer
public class LineSequencer extends Object
Builds a sequence from a set of LineStrings so that they are ordered end to end. A sequence is a complete non-repeating list of the linear components of the input. Each linestring is oriented so that identical endpoints are adjacent in the list.

A typical use case is to convert a set of unoriented geometric links from a linear network (e.g. such as block faces on a bus route) into a continuous oriented path through the network.

The input linestrings may form one or more connected sets. The input linestrings should be correctly noded, or the results may not be what is expected. The computed output is a single MultiLineString containing the ordered linestrings in the sequence.

The sequencing employs the classic Eulerian path graph algorithm. Since Eulerian paths are not uniquely determined, further rules are used to make the computed sequence preserve as much as possible of the input ordering. Within a connected subset of lines, the ordering rules are:

  • If there is degree-1 node which is the start node of an linestring, use that node as the start of the sequence
  • If there is a degree-1 node which is the end node of an linestring, use that node as the end of the sequence
  • If the sequence has no degree-1 nodes, use any node as the start
Note that not all arrangements of lines can be sequenced. For a connected set of edges in a graph, Euler's Theorem states that there is a sequence containing each edge once if and only if there are no more than 2 nodes of odd degree. If it is not possible to find a sequence, the isSequenceable() method will return false.
Version:
1.7

  • Field Details

    • graph

      private LineMergeGraph graph

    • factory

      private GeometryFactory factory

    • lineCount

      private int lineCount

    • isRun

      private boolean isRun

    • sequencedGeometry

      private Geometry sequencedGeometry

    • isSequenceable

      private boolean isSequenceable

  • Constructor Details

    • LineSequencer

      public LineSequencer()

  • Method Details

    • sequence

      public static Geometry sequence(Geometry geom)

    • isSequenced

      public static boolean isSequenced(Geometry geom)
      Tests whether a Geometry is sequenced correctly. LineStrings are trivially sequenced. MultiLineStrings are checked for correct sequencing. Otherwise, isSequenced is defined to be true for geometries that are not lineal.
      Parameters:
      geom - the geometry to test
      Returns:
      true if the geometry is sequenced or is not lineal

    • add

      public void add(Collection geometries)
      Adds a Collection of Geometrys to be sequenced. May be called multiple times. Any dimension of Geometry may be added; the constituent linework will be extracted.
      Parameters:
      geometries - a Collection of geometries to add

    • add

      public void add(Geometry geometry)
      Adds a Geometry to be sequenced. May be called multiple times. Any dimension of Geometry may be added; the constituent linework will be extracted.
      Parameters:
      geometry - the geometry to add

    • addLine

      private void addLine(LineString lineString)

    • isSequenceable

      public boolean isSequenceable()
      Tests whether the arrangement of linestrings has a valid sequence.
      Returns:
      true if a valid sequence exists.

    • getSequencedLineStrings

      public Geometry getSequencedLineStrings()
      Returns the LineString or MultiLineString built by the sequencing process, if one exists.
      Returns:
      the sequenced linestrings, or null if a valid sequence does not exist

    • computeSequence

      private void computeSequence()

    • findSequences

      private List findSequences()

    • hasSequence

      private boolean hasSequence(Subgraph graph)
      Tests whether a complete unique path exists in a graph using Euler's Theorem.
      Parameters:
      graph - the subgraph containing the edges
      Returns:
      true if a sequence exists

    • findSequence

      private List findSequence(Subgraph graph)

    • findUnvisitedBestOrientedDE

      private static DirectedEdge findUnvisitedBestOrientedDE(Node node)
      Finds an DirectedEdge for an unvisited edge (if any), choosing the dirEdge which preserves orientation, if possible.
      Parameters:
      node - the node to examine
      Returns:
      the dirEdge found, or null if none were unvisited

    • addReverseSubpath

      private void addReverseSubpath(DirectedEdge de, ListIterator lit, boolean expectedClosed)

    • findLowestDegreeNode

      private static Node findLowestDegreeNode(Subgraph graph)

    • orient

      private List orient(List seq)
      Computes a version of the sequence which is optimally oriented relative to the underlying geometry.

      Heuristics used are:

      • If the path has a degree-1 node which is the start node of an linestring, use that node as the start of the sequence
      • If the path has a degree-1 node which is the end node of an linestring, use that node as the end of the sequence
      • If the sequence has no degree-1 nodes, use any node as the start (NOTE: in this case could orient the sequence according to the majority of the linestring orientations)
      Parameters:
      seq - a List of DirectedEdges
      Returns:
      a List of DirectedEdges oriented appropriately

    • reverse

      private List reverse(List seq)
      Reverse the sequence. This requires reversing the order of the dirEdges, and flipping each dirEdge as well
      Parameters:
      seq - a List of DirectedEdges, in sequential order
      Returns:
      the reversed sequence

    • buildSequencedGeometry

      private Geometry buildSequencedGeometry(List sequences)
      Builds a geometry (LineString or MultiLineString ) representing the sequence.
      Parameters:
      sequences - a List of Lists of DirectedEdges with LineMergeEdges as their parent edges.
      Returns:
      the sequenced geometry, or null if no sequence exists

    • reverse

      private static LineString reverse(LineString line)