com.vividsolutions.jts.triangulate.quadedge

Class QuadEdgeSubdivision


  • public class QuadEdgeSubdivision
extends Object
    A class that contains the QuadEdges representing a planar subdivision that models a triangulation. The subdivision is constructed using the quadedge algebra defined in the classs QuadEdge. All metric calculations are done in the Vertex class. In addition to a triangulation, subdivisions support extraction of Voronoi diagrams. This is easily accomplished, since the Voronoi diagram is the dual of the Delaunay triangulation.

    Subdivisions can be provided with a tolerance value. Inserted vertices which are closer than this value to vertices already in the subdivision will be ignored. Using a suitable tolerance value can prevent robustness failures from happening during Delaunay triangulation.

    Subdivisions maintain a frame triangle around the client-created edges. The frame is used to provide a bounded "container" for all edges within a TIN. Normally the frame edges, frame connecting edges, and frame triangles are not included in client processing.

    • Constructor Detail

      • QuadEdgeSubdivision

        public QuadEdgeSubdivision(Envelope env,
                           double tolerance)
        Creates a new instance of a quad-edge subdivision based on a frame triangle that encloses a supplied bounding box. A new super-bounding box that contains the triangle is computed and stored.
        Parameters:
        env - the bouding box to surround
        tolerance - the tolerance value for determining if two sites are equal

    • Method Detail

      • getTriangleEdges

        public static void getTriangleEdges(QuadEdge startQE,
                                    QuadEdge[] triEdge)
        Gets the edges for the triangle to the left of the given QuadEdge.
        Parameters:
        startQE -
        triEdge -
        Throws:
        IllegalArgumentException - if the edges do not form a triangle

      • getTolerance

        public double getTolerance()
        Gets the vertex-equality tolerance value used in this subdivision
        Returns:
        the tolerance value

      • getEnvelope

        public Envelope getEnvelope()
        Gets the envelope of the Subdivision (including the frame).
        Returns:
        the envelope

      • getEdges

        public Collection getEdges()
        Gets the collection of base QuadEdges (one for every pair of vertices which is connected).
        Returns:
        a collection of QuadEdges

      • setLocator

        public void setLocator(QuadEdgeLocator locator)
        Sets the QuadEdgeLocator to use for locating containing triangles in this subdivision.
        Parameters:
        locator - a QuadEdgeLocator

      • makeEdge

        public QuadEdge makeEdge(Vertex o,
                         Vertex d)
        Creates a new quadedge, recording it in the edges list.
        Parameters:
        o -
        d -
        Returns:
        a new quadedge

      • connect

        public QuadEdge connect(QuadEdge a,
                        QuadEdge b)
        Creates a new QuadEdge connecting the destination of a to the origin of b, in such a way that all three have the same left face after the connection is complete. The quadedge is recorded in the edges list.
        Parameters:
        a -
        b -
        Returns:
        a quadedge

      • delete

        public void delete(QuadEdge e)
        Deletes a quadedge from the subdivision. Linked quadedges are updated to reflect the deletion.
        Parameters:
        e - the quadedge to delete

      • locateFromEdge

        public QuadEdge locateFromEdge(Vertex v,
                               QuadEdge startEdge)
        Locates an edge of a triangle which contains a location specified by a Vertex v. The edge returned has the property that either v is on e, or e is an edge of a triangle containing v. The search starts from startEdge amd proceeds on the general direction of v.

        This locate algorithm relies on the subdivision being Delaunay. For non-Delaunay subdivisions, this may loop for ever.

        Parameters:
        v - the location to search for
        startEdge - an edge of the subdivision to start searching at
        Throws:
        LocateFailureException - if the location algorithm fails to converge in a reasonable number of iterations

      • locate

        public QuadEdge locate(Vertex v)
        Finds a quadedge of a triangle containing a location specified by a Vertex, if one exists.
        Parameters:
        v - the vertex to locate
        Returns:
        a quadedge on the edge of a triangle which touches or contains the location or null if no such triangle exists

      • locate

        public QuadEdge locate(Coordinate p)
        Finds a quadedge of a triangle containing a location specified by a Coordinate, if one exists.
        Parameters:
        p - the Coordinate to locate
        Returns:
        a quadedge on the edge of a triangle which touches or contains the location or null if no such triangle exists

      • locate

        public QuadEdge locate(Coordinate p0,
                       Coordinate p1)
        Locates the edge between the given vertices, if it exists in the subdivision.
        Parameters:
        p0 - a coordinate
        p1 - another coordinate
        Returns:
        the edge joining the coordinates, if present or null if no such edge exists

      • insertSite

        public QuadEdge insertSite(Vertex v)
        Inserts a new site into the Subdivision, connecting it to the vertices of the containing triangle (or quadrilateral, if the split point falls on an existing edge).

        This method does NOT maintain the Delaunay condition. If desired, this must be checked and enforced by the caller.

        This method does NOT check if the inserted vertex falls on an edge. This must be checked by the caller, since this situation may cause erroneous triangulation

        Parameters:
        v - the vertex to insert
        Returns:
        a new quad edge terminating in v

      • isFrameEdge

        public boolean isFrameEdge(QuadEdge e)
        Tests whether a QuadEdge is an edge incident on a frame triangle vertex.
        Parameters:
        e - the edge to test
        Returns:
        true if the edge is connected to the frame triangle

      • isFrameBorderEdge

        public boolean isFrameBorderEdge(QuadEdge e)
        Tests whether a QuadEdge is an edge on the border of the frame facets and the internal facets. E.g. an edge which does not itself touch a frame vertex, but which touches an edge which does.
        Parameters:
        e - the edge to test
        Returns:
        true if the edge is on the border of the frame

      • isFrameVertex

        public boolean isFrameVertex(Vertex v)
        Tests whether a vertex is a vertex of the outer triangle.
        Parameters:
        v - the vertex to test
        Returns:
        true if the vertex is an outer triangle vertex

      • isOnEdge

        public boolean isOnEdge(QuadEdge e,
                        Coordinate p)
        Tests whether a Coordinate lies on a QuadEdge, up to a tolerance determined by the subdivision tolerance.
        Parameters:
        e - a QuadEdge
        p - a point
        Returns:
        true if the vertex lies on the edge

      • isVertexOfEdge

        public boolean isVertexOfEdge(QuadEdge e,
                              Vertex v)
        Tests whether a Vertex is the start or end vertex of a QuadEdge, up to the subdivision tolerance distance.
        Parameters:
        e -
        v -
        Returns:
        true if the vertex is a endpoint of the edge

      • getVertices

        public Collection getVertices(boolean includeFrame)
        Gets the unique Vertexes in the subdivision, including the frame vertices if desired.
        Parameters:
        includeFrame - true if the frame vertices should be included
        Returns:
        a collection of the subdivision vertices
        See Also:
        getVertexUniqueEdges(boolean)

      • getVertexUniqueEdges

        public List getVertexUniqueEdges(boolean includeFrame)
        Gets a collection of QuadEdges whose origin vertices are a unique set which includes all vertices in the subdivision. The frame vertices can be included if required.

        This is useful for algorithms which require traversing the subdivision starting at all vertices. Returning a quadedge for each vertex is more efficient than the alternative of finding the actual vertices using getVertices(boolean) and then locating quadedges attached to them.

        Parameters:
        includeFrame - true if the frame vertices should be included
        Returns:
        a collection of QuadEdge with the vertices of the subdivision as their origins

      • getPrimaryEdges

        public List getPrimaryEdges(boolean includeFrame)
        Gets all primary quadedges in the subdivision. A primary edge is a QuadEdge which occupies the 0'th position in its array of associated quadedges. These provide the unique geometric edges of the triangulation.
        Parameters:
        includeFrame - true if the frame edges are to be included
        Returns:
        a List of QuadEdges

      • visitTriangles

        public void visitTriangles(TriangleVisitor triVisitor,
                           boolean includeFrame)
        Visitors

      • getTriangleEdges

        public List getTriangleEdges(boolean includeFrame)
        Gets a list of the triangles in the subdivision, specified as an array of the primary quadedges around the triangle.
        Parameters:
        includeFrame - true if the frame triangles should be included
        Returns:
        a List of QuadEdge[3] arrays

      • getTriangleVertices

        public List getTriangleVertices(boolean includeFrame)
        Gets a list of the triangles in the subdivision, specified as an array of the triangle Vertexes.
        Parameters:
        includeFrame - true if the frame triangles should be included
        Returns:
        a List of Vertex[3] arrays

      • getTriangleCoordinates

        public List getTriangleCoordinates(boolean includeFrame)
        Gets the coordinates for each triangle in the subdivision as an array.
        Parameters:
        includeFrame - true if the frame triangles should be included
        Returns:
        a list of Coordinate[4] representing each triangle

      • getEdges

        public Geometry getEdges(GeometryFactory geomFact)
        Gets the geometry for the edges in the subdivision as a MultiLineString containing 2-point lines.
        Parameters:
        geomFact - the GeometryFactory to use
        Returns:
        a MultiLineString

      • getTriangles

        public Geometry getTriangles(GeometryFactory geomFact)
        Gets the geometry for the triangles in a triangulated subdivision as a GeometryCollection of triangular Polygons.
        Parameters:
        geomFact - the GeometryFactory to use
        Returns:
        a GeometryCollection of triangular Polygons

      • getVoronoiDiagram

        public Geometry getVoronoiDiagram(GeometryFactory geomFact)
        Gets the cells in the Voronoi diagram for this triangulation. The cells are returned as a GeometryCollection of Polygons

        The userData of each polygon is set to be the Coordinate of the cell site. This allows easily associating external data associated with the sites to the cells.

        Parameters:
        geomFact - a geometry factory
        Returns:
        a GeometryCollection of Polygons

      • getVoronoiCellPolygons

        public List getVoronoiCellPolygons(GeometryFactory geomFact)
        Gets a List of Polygons for the Voronoi cells of this triangulation.

        The userData of each polygon is set to be the Coordinate of the cell site. This allows easily associating external data associated with the sites to the cells.

        Parameters:
        geomFact - a geometry factory
        Returns:
        a List of Polygons

      • getVoronoiCellPolygon

        public Polygon getVoronoiCellPolygon(QuadEdge qe,
                                     GeometryFactory geomFact)
        Gets the Voronoi cell around a site specified by the origin of a QuadEdge.

        The userData of the polygon is set to be the Coordinate of the site. This allows attaching external data associated with the site to this cell polygon.

        Parameters:
        qe - a quadedge originating at the cell site
        geomFact - a factory for building the polygon
        Returns:
        a polygon indicating the cell extent