The concept TriangulationDataStructure_2::Vertex describes the type used by a TriangulationDataStructure_2 to store the vertices.
Some of the requirements listed below are of geometric nature and are optional when using the triangulation data structure class alone. They became required when the triangulation data structure is plugged into a triangulation.
TriangulationDataStructure_2::Vertex::Point  
Optional for the triangulation data
structure used alone.

In order to obtain new vertices or destruct unused vertices, the user must call the create_vertex() and delete_vertex() methods of the triangulation data structure.
Point  v.point () const  returns the geometric information of v. 
Face_handle  v.face () const  returns a face of the triangulation having v as vertex. 
void  v.set_point ( Point p)  sets the geometric information to p. 
void  v.set_face ( Face_handle f)  sets the incident face to f. 
istream&  istream& is >> & v  Inputs the noncombinatorial information possibly stored in the vertex. 
ostream&  ostream& os << v  Outputs the non combinatorial operation possibly stored in the vertex. 