CGAL 6.0.1  dD Triangulations

The TriangulationDataStructure
concept describes objects responsible for storing and maintaining the combinatorial part of a \( d\)dimensional pure simplicial complex that has the topology of the \( d\)dimensional sphere \( \mathbb{S}^d\) with \( d\in[2,D]\). Since the simplicial \( d\)complex is pure, all faces are subfaces of some \( d\)simplex. And since it has the topology of the sphere \( \mathbb{S}^d\), it is manifold, thus any \( d1\)face belongs to exactly two \( d\)dimensional full cells.
The concept TriangulationDataStructure
includes two subconcepts TriangulationDataStructure::Vertex
and TriangulationDataStructure::FullCell
.
Possible values for the current dimension \( d\) include
This corresponds to a single vertex and a single full cell, which is also the unique vertex and the unique full cell in the TriangulationDataStructure
. In a geometric realization of the TriangulationDataStructure
(e.g., in a Triangulation<TriangulationTraits_, TriangulationDataStructure_>
or a Delaunay_triangulation<DelaunayTriangulationTraits_, TriangulationDataStructure_>
), this vertex corresponds to the vertex at infinity.
This corresponds to two vertices, each incident to one \( 0\)face; the two full cells being neighbors of each other. This is the unique triangulation of the \( 0\)sphere.
An \( i\)simplex is a simplex with \( i+1\) vertices. An \( i\)simplex \( \sigma\) is incident to a \( j\)simplex \( \sigma'\), \( j<i\), if and only if \( \sigma'\) is a proper face of \( \sigma\).
We call a \( 0\)simplex a vertex, a \( (d1)\)simplex a facet and a \( d\)simplex a full cell. A face can have any dimension. Two full cells are neighbors if they share a facet. Two faces are incident if one is included in the other.
Input/Output
The information stored in the iostream
is:
tds.maximal_dimension()
),The indices of vertices and full cells correspond to the order in the file; the user cannot control it. The classes Vertex
and Full_cell
have to provide the relevant I/O operators (possibly empty).
CGAL::Triangulation_data_structure<Dimensionality, TriangulationDSVertex_, TriangulationDSFullCell_>
Concepts  
concept  FullCell 
The concept TriangulationDataStructure::FullCell describes the type used by a TriangulationDataStructure to store the full cells. More...  
concept  Vertex 
The concept TriangulationDataStructure::Vertex describes the type used by a TriangulationDataStructure to store the vertices. More...  
Types  
typedef unspecified_type  Vertex 
The vertex type, requirements for this type are described in the concept TriangulationDataStructure::Vertex .  
typedef unspecified_type  Full_cell 
The full cell type, requirements for this type are described in the concept TriangulationDataStructure::FullCell .  
typedef unspecified_type  Full_cell_data 
A model of the concept FullCellData .  
typedef unspecified_type  Facet 
The facet type, for describing faces of the triangulation with codimension 1.  
typedef unspecified_type  Face 
The face type, which must be a model of the concept TriangulationDSFace .  
Handles  
Vertices and full cells are manipulated via handles. Handles support the usual two dereference operators and  
typedef unspecified_type  Vertex_handle 
Handle to a Vertex .  
typedef unspecified_type  Vertex_const_handle 
Const handle to a Vertex .  
typedef unspecified_type  Full_cell_handle 
Handle to a Full_cell .  
typedef unspecified_type  Full_cell_const_handle 
Const handle to a Full_cell .  
Iterators  
Vertices, facets and full cells can be iterated over using iterators. Iterators support the usual two dereference operators and  
typedef unspecified_type  Vertex_iterator 
Iterator over the list of vertices.  
typedef unspecified_type  Full_cell_iterator 
Iterator over the list of full cells.  
typedef unspecified_type  Facet_iterator 
Iterator over the facets of the complex.  
typedef unspecified_type  size_type 
Size type (an unsigned integral type).  
typedef unspecified_type  difference_type 
Difference type (a signed integral type).  
Creation  
TriangulationDataStructure (int dim=0)  
Creates an instance tds of type TriangulationDataStructure .  
Queries  
int  maximal_dimension () const 
Returns the maximal dimension of the full dimensional cells that can be stored in the triangulation tds .  
int  current_dimension () const 
Returns the dimension of the full dimensional cells stored in the triangulation.  
bool  empty () const 
Returns true if the triangulation contains nothing, returns false otherwise.  
size_type  number_of_vertices () const 
Returns the number of vertices in the triangulation.  
size_type  number_of_full_cells () const 
Returns the number of full cells in the triangulation.  
bool  is_vertex (const Vertex_handle &v) const 
Tests whether v is a vertex of the triangulation.  
bool  is_full_cell (const Full_cell_handle &c) const 
Tests whether c is a full cell of the triangulation.  
template<typename TraversalPredicate , typename OutputIterator >  
Facet  gather_full_cells (Full_cell_handle start, TraversalPredicate &tp, OutputIterator &out) const 
This function computes (gathers) a connected set of full cells satisfying a common criterion.  
template<typename OutputIterator >  
OutputIterator  incident_full_cells (Vertex_handle v, OutputIterator out) const 
Inserts in out all the full cells that are incident to the vertex v , i.e., the full cells that have the Vertex v as a vertex.  
template<typename OutputIterator >  
OutputIterator  incident_full_cells (const Face &f, OutputIterator out) const 
Inserts in out all the full cells that are incident to the face f , i.e., the full cells that have the Face f as a subface.  
template<typename OutputIterator >  
OutputIterator  star (const Face &f, OutputIterator out) const 
Inserts in out all the full cells that share at least one vertex with the Face f .  
template<typename OutputIterator >  
OutputIterator  incident_faces (Vertex_handle v, const int dim, OutputIterator out) 
Constructs all the Face s of dimension dim incident to Vertex v and inserts them in the OutputIterator out .  
Accessing the Vertices  
Vertex_handle  vertex (Full_cell_handle c, const int i) const 
Returns a handle to the i th Vertex of the Full_cell c .  
int  mirror_index (Full_cell_handle c, int i) const 
Returns the index of c as a neighbor of its i th neighbor.  
Vertex_handle  mirror_vertex (Full_cell_handle c, int i) const 
Returns the vertex of the i th neighbor of c that is not vertex of c .  
Vertex_iterator  vertices_begin () 
Iterator to the first vertex of tds .  
Vertex_iterator  vertices_end () 
Iterator referring beyond the last vertex of tds .  
Accessing the Full Cells  
Full_cell_handle  full_cell (Vertex_handle v) const 
Returns a full cell incident to Vertex v .  
Full_cell_handle  neighbor (Full_cell_handle c, int i) const 
Returns a Full_cell_handle pointing to the Full_cell opposite to the i th vertex of c .  
Full_cell_iterator  full_cells_begin () 
Iterator to the first full cell of tds .  
Full_cell_iterator  full_cells_end () 
Iterator referring beyond the last full cell of tds .  
Faces and Facets  
Facet_iterator  facets_begin () 
Iterator to the first facet of the triangulation.  
Facet_iterator  facets_end () 
Iterator referring beyond the last facet of the triangulation.  
Full_cell_handle  full_cell (const Facet &f) const 
Returns a full cell containing the facet f  
int  index_of_covertex (const Facet &f) const 
Returns the index of vertex of the full cell c=tds.full_cell(f) which does not belong to c .  
Vertex Insertion  
Vertex_handle  insert_in_full_cell (Full_cell_handle c) 
Inserts a new vertex v in the full cell c and returns a handle to it.  
Vertex_handle  insert_in_face (const Face &f) 
Inserts a vertex in the triangulation data structure by subdividing the Face f .  
Vertex_handle  insert_in_facet (const Facet &ft) 
Inserts a vertex in the triangulation data structure by subdividing the Facet ft .  
template<class ForwardIterator >  
Vertex_handle  insert_in_hole (ForwardIterator start, ForwardIterator end, Facet f) 
This is an advanced function.  
template<class ForwardIterator , class OutputIterator >  
Vertex_handle  insert_in_hole (ForwardIterator start, ForwardIterator end, Facet f, OutputIterator out) 
Same as above, but handles to the new full cells are appended to the out output iterator.  
Vertex_handle  insert_increase_dimension (Vertex_handle star) 
Transforms a triangulation of the sphere \( \mathbb{S}^d\) into the triangulation of the sphere \( \mathbb{S}^{d+1}\) by adding a new vertex v .  
Full_cell_handle  new_full_cell () 
Adds a new full cell to tds and returns a handle to it.  
Vertex_handle  new_vertex () 
Adds a new vertex to tds and returns a handle to it.  
void  associate_vertex_with_full_cell (Full_cell_handle c, int i, Vertex_handle v) 
Sets the i th vertex of c to v and, if v != Vertex_handle() , sets c as the incident full cell of v .  
void  set_neighbors (Full_cell_handle ci, int i, Full_cell_handle cj, int j) 
Sets the neighbor opposite to vertex i of Full_cell ci to cj .  
void  set_current_dimension (int d) 
Forces the current dimension of the complex to d .  
Vertex Removal  
void  clear () 
Reinitializes tds to the empty complex.  
Vertex_handle  collapse_face (const Face &f) 
Contracts the Face f to a single vertex.  
void  remove_decrease_dimension (Vertex_handle v, Vertex_handle star) 
This method does exactly the opposite of insert_increase_dimension() : v is removed, full cells not containing star are removed, full cells containing star but not v lose vertex star , full cells containing star and v lose vertex v (see Figure Figure 49.5).  
void  delete_vertex (Vertex_handle v) 
This is an advanced function.  
void  delete_full_cell (Full_cell_handle c) 
This is an advanced function.  
template<typename ForwardIterator >  
void  delete_full_cells (ForwardIterator start, ForwardIterator end) 
This is an advanced function.  
Validity Check  
bool  is_valid (bool verbose=false) const 
This is a function for debugging purpose.  
std::istream &  operator>> (std::istream &is, TriangulationDataStructure &tds) 
Reads a combinatorial triangulation from is and assigns it to tds .  
std::ostream &  operator<< (std::ostream &os, const TriangulationDataStructure &tds) 
Writes tds into the output stream os .  
The facet type, for describing faces of the triangulation with codimension 1.
The constructor Facet(c,i)
constructs a Facet
representing the facet of full cell c
opposite to its i
th vertex. Its dimension is current_dimension()1
.
TriangulationDataStructure::TriangulationDataStructure  (  int  dim = 0  ) 
Creates an instance tds
of type TriangulationDataStructure
.
The maximal dimension of its full cells is dim
and tds
is initialized to the empty triangulation. Thus, tds
.current_dimension()
equals 2
. The parameter dim
can be ignored by the constructor if it is already known at compiletime. Otherwise, the following precondition holds:
dim>0
. Vertex_handle TriangulationDataStructure::collapse_face  (  const Face &  f  ) 
Contracts the Face f
to a single vertex.
Returns a handle to that vertex (see Figure Figure 49.1).
f
is a topological sphere of dimension tds
.current_dimension()
1).
int TriangulationDataStructure::current_dimension  (  )  const 
Returns the dimension of the full dimensional cells stored in the triangulation.
It holds that tds
.current_dimension()=2
if and only if tds
.empty()
is true
.
d
satisfies \( 2\leq d \leq\)tds
.maximal_dimension()
. void TriangulationDataStructure::delete_full_cell  (  Full_cell_handle  c  ) 
This is an advanced function.
Remove the full cell c
from the triangulation.
c
is a full cell of tds
. void TriangulationDataStructure::delete_full_cells  (  ForwardIterator  start, 
ForwardIterator  end  
) 
This is an advanced function.
Calls delete_full_cell
over an iterator range of value type Full_cell_handle
.
void TriangulationDataStructure::delete_vertex  (  Vertex_handle  v  ) 
This is an advanced function.
Remove the vertex v
from the triangulation.
v
is a vertex of tds
. Full_cell_handle TriangulationDataStructure::full_cell  (  Vertex_handle  v  )  const 
Returns a full cell incident to Vertex
v
.
Note that this full cell is not unique (v
is typically incident to more than one full cell).
v != Vertex_handle
Full_cell_iterator TriangulationDataStructure::full_cells_begin  (  ) 
Iterator to the first full cell of tds
.
User has no control on the order.
Facet TriangulationDataStructure::gather_full_cells  (  Full_cell_handle  start, 
TraversalPredicate &  tp,  
OutputIterator &  out  
)  const 
This function computes (gathers) a connected set of full cells satisfying a common criterion.
Call them good full cells. It is assumed that the argument start
is a good full cell. The full cells are then recursively explored by examining if, from a given good full cell, its adjacent full cells are also good.
The argument tp
is a predicate, i.e. a function or a functor providing operator()
, that takes as argument a Facet
whose Full_cell
is good. The predicate must return true
if the traversal of that Facet
leads to a good full cell.
All the good full cells are output into the last argument out
.
Returns a facet on the boundary of the set of cells.
start != Full_cell_handle()
and start
is a good cell. OutputIterator TriangulationDataStructure::incident_faces  (  Vertex_handle  v, 
const int  dim,  
OutputIterator  out  
) 
Constructs all the Face
s of dimension dim
incident to Vertex
v and inserts them in the OutputIterator out
.
If dim >=
tds
.current_dimension()
, then no Face
is constructed.
0 < dim
and v!=Vertex_handle()
. OutputIterator TriangulationDataStructure::incident_full_cells  (  const Face &  f, 
OutputIterator  out  
)  const 
Inserts in out
all the full cells that are incident to the face f
, i.e., the full cells that have the Face f
as a subface.
Returns the output iterator.
f.full_cell()!=Full_cell_handle()
. OutputIterator TriangulationDataStructure::incident_full_cells  (  Vertex_handle  v, 
OutputIterator  out  
)  const 
Inserts in out
all the full cells that are incident to the vertex v
, i.e., the full cells that have the Vertex v
as a vertex.
Returns the output iterator.
v!=Vertex_handle()
. Vertex_handle TriangulationDataStructure::insert_in_face  (  const Face &  f  ) 
Inserts a vertex in the triangulation data structure by subdividing the Face f
.
Returns a handle to the newly created Vertex
.
Vertex_handle TriangulationDataStructure::insert_in_facet  (  const Facet &  ft  ) 
Inserts a vertex in the triangulation data structure by subdividing the Facet ft
.
Returns a handle to the newly created Vertex
.
Vertex_handle TriangulationDataStructure::insert_in_full_cell  (  Full_cell_handle  c  ) 
Inserts a new vertex v
in the full cell c
and returns a handle to it.
The full cell c
is subdivided into tds
.current_dimension()
+1 full cells which share the vertex v
.
c
is a full cell of tds
. Vertex_handle TriangulationDataStructure::insert_in_hole  (  ForwardIterator  start, 
ForwardIterator  end,  
Facet  f  
) 
This is an advanced function.
Removes the full cells in the range \( C=\)[s, e)
, inserts a vertex at position p
and fills the hole by connecting each face of the boundary to p
. A Vertex_handle
to the new Vertex
is returned. The facet ft
must lie on the boundary of \( C\) and its defining full cell, tr
.full_cell(ft)
must lie inside \( C\). Handles to the newly created full cells are output in the out
output iterator.
c
belongs to \( C\) and c>neighbor(i)
does not, with f=(c,i)
. \( H\), the union of full cells in \( C\), is simply connected and its boundary \( \partial H\) is a combinatorial triangulation of the sphere \( \mathbb{S}^{d1}\). All vertices of cells of \( C\) are on \( \partial H\).
Vertex_handle TriangulationDataStructure::insert_increase_dimension  (  Vertex_handle  star  ) 
Transforms a triangulation of the sphere \( \mathbb{S}^d\) into the triangulation of the sphere \( \mathbb{S}^{d+1}\) by adding a new vertex v
.
v
is used to triangulate one of the two halfspheres of \( \mathbb{S}^{d+1}\) ( \( v\) is added as \( (d+2)^{th}\) vertex to all full cells) and star
is used to triangulate the other halfsphere (all full cells that do not already have star as vertex are duplicated, and star
replaces v
in these full cells). The indexing of the vertices in the full cell is such that, if f
was a full cell of maximal dimension in the initial complex, then (f,v)
, in this order, is the corresponding full cell in the updated triangulation. A handle to v
is returned (see Figure Figure 49.5).
star
can be omitted (it is ignored), otherwise the current dimension must be strictly less than the maximal dimension and star
must be a vertex of tds
.
bool TriangulationDataStructure::is_valid  (  bool  verbose = false  )  const 
This is a function for debugging purpose.
Partially checks whether tds
is indeed a triangulation.
It must at least
tds
by calling their respective is_valid
method. current_dimension()+1
). tds
.current_dimension()
vertices with each of its neighbor. When verbose
is set to true
, messages are printed to give a precise indication on the kind of invalidity encountered.
Returns true
if all the tests pass, false
if any test fails. See the documentation for the models of this concept to see the additional (if any) validity checks that they implement.
int TriangulationDataStructure::maximal_dimension  (  )  const 
Returns the maximal dimension of the full dimensional cells that can be stored in the triangulation tds
.
int TriangulationDataStructure::mirror_index  (  Full_cell_handle  c, 
int  i  
)  const 
Returns the index of c
as a neighbor of its i
th neighbor.
tds
.current_dimension
() and c!=Full_cell_handle()
. Vertex_handle TriangulationDataStructure::mirror_vertex  (  Full_cell_handle  c, 
int  i  
)  const 
Returns the vertex of the i
th neighbor of c
that is not vertex of c
.
tds
.current_dimension
() and c!=Full_cell_handle()
. Full_cell_handle TriangulationDataStructure::neighbor  (  Full_cell_handle  c, 
int  i  
)  const 
Returns a Full_cell_handle
pointing to the Full_cell
opposite to the i
th vertex of c
.
tds
.current_dimension()
and c != Full_cell_handle()
Full_cell_handle TriangulationDataStructure::new_full_cell  (  ) 
Adds a new full cell to tds
and returns a handle to it.
The new full cell has no vertices and no neighbors yet.
Vertex_handle TriangulationDataStructure::new_vertex  (  ) 
Adds a new vertex to tds
and returns a handle to it.
The new vertex has no associated full cell nor index yet.
std::istream & TriangulationDataStructure::operator>>  (  std::istream &  is, 
TriangulationDataStructure &  tds  
) 
Reads a combinatorial triangulation from is
and assigns it to tds
.
tds
.maximal_dimension()
. void TriangulationDataStructure::remove_decrease_dimension  (  Vertex_handle  v, 
Vertex_handle  star  
) 
This method does exactly the opposite of insert_increase_dimension()
: v
is removed, full cells not containing star
are removed, full cells containing star
but not v
lose vertex star
, full cells containing star
and v
lose vertex v
(see Figure Figure 49.5).
star
or v
. Edge starv
exists in the triangulation and current_dimension() != 2
. void TriangulationDataStructure::set_current_dimension  (  int  d  ) 
Forces the current dimension of the complex to d
.
maximal_dimension()
. void TriangulationDataStructure::set_neighbors  (  Full_cell_handle  ci, 
int  i,  
Full_cell_handle  cj,  
int  j  
) 
Sets the neighbor opposite to vertex i
of Full_cell
ci
to cj
.
Sets the neighbor opposite to vertex j
of Full_cell
cj
to ci
.
OutputIterator TriangulationDataStructure::star  (  const Face &  f, 
OutputIterator  out  
)  const 
Inserts in out
all the full cells that share at least one vertex with the Face f
.
Returns the output iterator.
f.full_cell()!=Full_cell_handle()
. Vertex_handle TriangulationDataStructure::vertex  (  Full_cell_handle  c, 
const int  i  
)  const 
Returns a handle to the i
th Vertex
of the Full_cell
c
.
tds
.current_dimension()
and c!=Full_cell_handle()
. Vertex_iterator TriangulationDataStructure::vertices_begin  (  ) 
Iterator to the first vertex of tds
.
User has no control on the order.