/// \defgroup PkgTDS3 3D Triangulation Data Structure Reference

/// \defgroup PkgTDS3Concepts Concepts
/// \ingroup PkgTDS3

/// \defgroup PkgTDS3Classes Classes
/// \ingroup PkgTDS3

/*!
\addtogroup PkgTDS3
\todo check generated documentation
\cgalPkgDescriptionBegin{3D Triangulation Data Structure,PkgTDS3Summary}
\cgalPkgPicture{tds3_small.png}
\cgalPkgSummaryBegin
\cgalPkgAuthors{Sylvain Pion and Monique Teillaud}
\cgalPkgDesc{This package provides a data structure to store a three-dimensional triangulation that has the topology of a three-dimensional sphere.  The package acts as a container for the vertices  and cells of the triangulation  and provides basic  combinatorial operations on the triangulation.}
\cgalPkgManuals{Chapter_3D_Triangulation_Data_Structure,PkgTDS3}
\cgalPkgSummaryEnd
\cgalPkgShortInfoBegin
\cgalPkgSince{2.1}
\cgalPkgBib{cgal:pt-tds3}
\cgalPkgLicense{\ref licensesGPL "GPL"}
\cgalPkgShortInfoEnd
\cgalPkgDescriptionEnd

The triangulation data structure is able to represent a
triangulation of a topological sphere \f$ S^d\f$ of \f$ \R^{d+1}\f$, for 
\f$ d \in \{-1,0,1,2,3\}\f$. (See  \ref TDS3secintro.)

The vertex class of a 3D-triangulation data structure must define
a number of types and operations. 
The requirements that are of geometric nature are required only when
the triangulation data structure is used as a layer for the geometric
triangulation classes. (See Section  \ref TDS3secdesign.)

The cell class of a triangulation data structure stores
four handles to its four vertices and four handles to its four
neighbors. The vertices are indexed 0, 1, 2, and 3 in a consistent order.
The neighbor indexed \f$ i\f$ lies opposite to vertex `i`.

In degenerate dimensions, cells are used to store faces of maximal
dimension: in dimension 2, each cell represents only one
facet of index 3, and 3 edges \f$ (0,1)\f$, \f$ (1,2)\f$ and \f$ (2,0)\f$; in
dimension 1, each cell represents one edge \f$ (0,1)\f$. (See 
Section  \ref TDS3secintro.)

\cgalClassifedRefPages

## Concepts ##

- `TriangulationDataStructure_3`
- `TriangulationDataStructure_3::Cell`
- `TriangulationDataStructure_3::Vertex`
- `TriangulationDSCellBase_3`
- `TriangulationDSVertexBase_3`

## Classes ##

- `CGAL::Triangulation_data_structure_3<TriangulationDSVertexBase_3,TriangulationDSCellBase_3>` is a model for the concept of the 3D-triangulation data structure `TriangulationDataStructure_3`. It is templated by base classes for vertices and cells.

\cgal provides base vertex classes and base cell classes:

- `CGAL::Triangulation_ds_cell_base_3<>`
- `CGAL::Triangulation_ds_vertex_base_3<>`
- `CGAL::Triangulation_cell_base_3<TriangulationTraits_3, TriangulationDSCellBase_3>`
- `CGAL::Triangulation_vertex_base_3<TriangulationTraits_3, TriangulationDSVertexBase_3>`
- `CGAL::Triangulation_hierarchy_vertex_base_3<TriangulationVertexBase_3>`

## Helper Classes ##

- `CGAL::Triangulation_utils_3` defines operations on the indices of vertices and neighbors within
a cell of a triangulation.

*/