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## SegmentVoronoiDiagramDataStructure_2

### Definition

The concept SegmentVoronoiDiagramDataStructure_2 refines the concept ApolloniusGraphDataStructure_2. In addition it provides two methods for the merging of two vertices joined by an edge of the data structure, and the splitting of a vertex into two. The method that merges two vertices, called join_vertices identifies the two vertices and deletes their common two faces. The method that splits a vertex, called split_vertex introduces a new vertex that shares an edge and two faces with the old vertex (see figure below). Notice that the join_vertices and split_vertex operations are complementary, in the sense that one reverses the action of the other.

Figure: The join and split operations. Left to right: The vertex v is split into v1 and v2. The faces f and g are inserted after f1 and f2, respectively, in the counter-clockwise sense. The vertices v1, v2 and the faces f and g are returned as a boost tuple in that order. Right to left: The edge (f,i) is collapsed, and thus the vertices v1 and v2 are joined. The vertex v is returned.

We only describe the additional requirements with respect to the ApolloniusGraphDataStructure_2 concept.

### Refines

ApolloniusGraphDataStructure_2

### Modification

Vertex_handle | svdds.join_vertices ( Face_handle f, int i)
|  | Joins the vertices that are endpoints of the edge (f,i). It returns a vertex handle to common vertex.
boost::tuples::tuple<Vertex_handle, Vertex_handle, Face_handle, Face_handle>
svdds.split_vertex ( | Vertex_handle v, Face_handle f1, Face_handle f2)
|  | Splits the vertex v into two vertices v1 and v2. The common faces f and g of v1 and v2 are created after (in the counter-clockwise sense) the faces f1 and f2. The 4-tuple (v1,v2,f,g) is returned (see Fig. ).

### Has Models

CGAL::Triangulation_data_structure_2<Vb,Fb>

### See Also

TriangulationDataStructure_2
ApolloniusGraphDataStructure_2
SegmentVoronoiDiagramVertexBase_2
TriangulationFaceBase_2

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The CGAL Project . Tue, December 21, 2004 .