CGAL 5.6.3 - 2D Periodic Triangulations

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CGAL::Periodic_2_triangulation_2< Traits, Tds > Class Template Reference
2D Periodic Triangulations Reference » Main Classes

`#include <CGAL/Periodic_2_triangulation_2.h>`

## Inherits from

CGAL::Triangulation_cw_ccw_2.

Inherited by CGAL::Periodic_2_Delaunay_triangulation_2< Traits, Tds >.

## Definition

template<typename Traits, typename Tds>
class CGAL::Periodic_2_triangulation_2< Traits, Tds >

The class `Periodic_2_triangulation_2` represents a 2-dimensional triangulation of a point set in \( \mathbb T_c^2\).

Template Parameters

  Traits | is the geometric traits, it has to be instantiated by a model of the concept `Periodic_2TriangulationTraits_2`.
  Tds | is the triangulation data data structure and must be a model of `TriangulationDataStructure_2` whose vertex and face are models of `Periodic_2TriangulationVertexBase_2` and `Periodic_2TriangulationFaceBase_2`. It defaults to: CGAL::Triangulation_data_structure_2< CGAL::Periodic_2_triangulation_vertex_base_2<Gt>, CGAL::Periodic_2_triangulation_face_base_2<Gt> > > CGAL::Periodic_2_triangulation_face_base_2 The class Periodic_2_triangulation_face_base_2 is a model of the concept Periodic_2TriangulationFaceB... Definition: Periodic_2_triangulation_face_base_2.h:40 CGAL::Periodic_2_triangulation_vertex_base_2 The class Periodic_2_triangulation_vertex_base_2 is a model of the concept Periodic_2TriangulationVer... Definition: Periodic_2_triangulation_vertex_base_2.h:31 CGAL::Triangulation_data_structure_2

Traversal of the Triangulation

The periodic triangulation class provides several iterators and circulators that allow one to traverse it.

I/O

The I/O operators are defined for `iostream`. The format for the iostream is an internal format.

The information in the `iostream` is:

- the original domain
- the number of sheets of the covering space as in `number_of_sheets()`
- the number of vertices
- the non-combinatorial information of vertices (point resp. point-offset pairs, etc.)
- the number of faces
- the indices of the vertices of each face
- the indices of the neighbors of each face, where the index corresponds to the preceding list of faces
- the offsets corresponding to the vertices of the faces
- the non-combinatorial information of each face

Implementation

Locate is implemented by a randomized walk from a vertex of the face given as optional parameter (or from an arbitrary vertex of if no optional parameter is given).

Insertion of a point is done by locating a face that contains the point, and then splitting this face. Apart from the location, insertion takes a time \( O(1)\).

Removal of a vertex is more difficult than in the Euclidean space, since the star of a vertex may not be disjoint from the star of a virtual copy of that vertex. Therefore generic removal of vertices is not implemented. Several more constrained cases are implemented: the removal of the last vertex in the triangulation and the removal of a vertex of degree 3.

The face, edge, and vertex iterators on features are derived from their counterparts visiting all (non-virtual and virtual) features which are themselves derived from the corresponding iterators of the triangulation data structure.

See also
  `CGAL::Periodic_2_triangulation_2<Traits,Tds>`
  `CGAL::Periodic_2_triangulation_hierarchy_2<Tr>`
  `CGAL::Triangulation_2<Traits, Tds>`

## Public Types
enum | Iterator_type { STORED = 0 , UNIQUE , STORED_COVER_DOMAIN , UNIQUE_COVER_DOMAIN }
| The enum Iterator_type is defined by `Periodic_2_triangulation_2` to specify the behavior of geometric iterators. More...
enum | Locate_type { VERTEX = 0 , EDGE , FACE , EMPTY }
| The enum `Locate_type` is defined by `Periodic_2_triangulation_2` to specify which case occurs when locating a point in the triangulation. More...

## Public Member Functions
Vertex_handle | insert (const Point &p, Face_handle f=Face_handle())
Vertex_handle | insert (const Point &p, Locate_type lt, Face_handle loc, int li)
Vertex_handle | push_back (const Point &p)
template<class InputIterator >
int | insert (InputIterator first, InputIterator last)
Public Member Functions inherited from CGAL::Triangulation_cw_ccw_2
| Triangulation_cw_ccw_2 ()
int | ccw (const int i) const
int | cw (const int i) const

## Related Functions
(Note that these are not member functions.)
ostream & | operator<< (ostream &os, const Periodic_2_triangulation_2< Traits, Tds > &t)
| Writes the triangulation `t` into the stream `os`.
istream & | operator>> (istream &is, Triangulation_2< Traits, Tds > &t)
| Reads a triangulation from stream `is` and assigns it to `t`.

## Types
typedef Traits | Geom_traits
| the traits class.
typedef Tds | Triangulation_data_structure
| the triangulation data structure type.
typedef Geom_traits::Periodic_2_offset_2 | Offset
| the offset type.
typedef Geom_traits::Iso_rectangle_2 | Iso_rectangle
| the iso rectangle type.
typedef array< int, 2 > | Covering_sheets
| integer tuple to store the number of sheets in each direction of space.
typedef Geom_traits::Point_2 | Point
| the point type.
typedef Geom_traits::Segment_2 | Segment
| the segment type.
typedef Geom_traits::Triangle_2 | Triangle
| the triangle type.
typedef std::pair< Point, Offset > | Periodic_point
| represents a point-offset pair.
typedef array< Periodic_point, 2 > | Periodic_segment
| a pair of periodic points representing a segment in the periodic domain.
typedef array< Periodic_point, 3 > | Periodic_triangle
| a triple of periodic points representing a triangle in the periodic domain.
typedef Tds::Vertex | Vertex
| the vertex type.
typedef Tds::Face | Face
| the face type.
typedef Tds::Edge | Edge
| the edge type.
typedef Tds::size_type | size_type
| size type (an unsigned integral type).
typedef Tds::difference_type | difference_type
| difference type (a signed integral type).

## Handles, Iterators and Circulators
The vertices and faces of the triangulations are accessed through `handles`, `iterators` and `circulators`. The handles are CGAL models of the concept `Handle` which basically offers the two dereference operators and `->`. The iterators and circulators are all bidirectional and non-mutable. The circulators and iterators are convertible to handles with the same value type, so that whenever a handle appear in the parameter list of a function, an appropriate iterator or circulator can be passed as well. The edges of the triangulation can also be visited through iterators and circulators, the edge circulators and iterators are also bidirectional and non-mutable.
typedef Tds::Vertex_handle | Vertex_handle
| handle to a vertex.
typedef Tds::Face_handle | Face_handle
| handle to a face.
typedef Tds::Face_iterator | Face_iterator
| iterator over all faces.
typedef Tds::Edge_iterator | Edge_iterator
| iterator over all edges.
typedef Tds::Vertex_iterator | Vertex_iterator
| iterator over all vertices.
typedef unspecified_type | Unique_vertex_iterator
| iterator over the vertices whose corresponding points lie in the original domain, i.e.
typedef Face_iterator | Finite_faces_iterator
typedef Edge_iterator | Finite_edges_iterator
typedef Vertex_iterator | Finite_vertices_iterator
typedef Face_iterator | All_faces_iterator
typedef unspecified_type | Face_circulator
| circulator over all faces incident to a given vertex.
typedef unspecified_type | Edge_circulator
| circulator over all edges incident to a given vertex.
typedef unspecified_type | Vertex_circulator
| circulator over all vertices adjacent to a given vertex.

## Geometric iterators:
typedef unspecified_type | Periodic_triangle_iterator
| iterator over the triangles corresponding to faces of the triangulation.
typedef unspecified_type | Periodic_segment_iterator
| iterator over the segments corresponding to edges of the triangulation.
typedef unspecified_type | Periodic_point_iterator
| iterator over the points corresponding to vertices of the triangulation.

## Creation
| Triangulation_2 (const Iso_rectangle &domain=Iso_rectangle(0, 0, 1, 1), const Geom_traits &traits=Geom_traits())
| Introduces an empty triangulation `t` with `domain` as original domain.
| Triangulation_2 (const Triangulation_2 &tr)
| Copy constructor.
Triangulation_2 | operator= (const Triangulation_2< Traits, Tds > &tr)
| Assignment.
void | swap (Triangulation_2 &tr)
| The triangulations `tr` and `this` are swapped.
void | clear ()
| Deletes all faces and vertices resulting in an empty triangulation.

## Access Functions
The responsibility of keeping a valid triangulation belongs to the user when using advanced operations allowing a direct manipulation of the `tds`.
const Geom_traits & | geom_traits () const
| Returns a const reference to the triangulation traits object.
const Triangulation_data_structure_2 & | tds () const
| Returns a const reference to the triangulation data structure.
Iso_rectangle | domain () const
| Returns the original domain.
Covering_sheets | number_of_sheets () const
| Returns the number of sheets of the covering space the triangulation is currently computed in.
int | dimension () const
| Returns the dimension of the convex hull.
size_type | number_of_vertices () const
| Returns the number of vertices.
size_type | number_of_faces () const
| Returns the number of faces.
size_type | number_of_stored_vertices () const
| Returns the number of vertices in the data structure.
size_type | number_of_stored_faces () const
| Returns the number of faces in the data structure.

## Non const access
Advanced This method is mainly a help for users implementing their own triangulation algorithms.
Triangulation_data_structure_2 & | tds ()
| This is an advanced function.

## Non-constant-time access functions
size_type | number_of_edges () const
| Returns the number of edges.
size_type | number_of_stored_edges () const
| Returns the number of edges in the data structure.

## Non-constant-time queries and conversions
Advanced It is not recommended to interfere with the built-in covering management. Especially a premature conversion to the 1-sheeted covering space might lead to problems when modifying the triangulation later.
bool | is_extensible_triangulation_in_1_sheet_h1 () const
| This is an advanced function.
bool | is_extensible_triangulation_in_1_sheet_h2 () const
| This is an advanced function.
bool | is_triangulation_in_1_sheet () const
| This is an advanced function.
void | convert_to_1_sheeted_covering ()
| This is an advanced function.
void | convert_to_9_sheeted_covering ()
| This is an advanced function.

## Geometric access functions
Periodic_point | periodic_point (const Vertex_handle v) const
| Returns the periodic point given by vertex `v`.
Periodic_point | periodic_point (const Face_handle f, int i) const
| If `this` is represented in the 1-sheeted covering space, this function returns the periodic point given by the \( i\)-th vertex of face `f`, that is the point in the original domain and the offset of the vertex in `f`.
Periodic_segment | periodic_segment (const Face_handle f, int i) const
| Returns the periodic segment formed by the two point-offset pairs corresponding to the two vertices of edge `(f,i)`.
Periodic_segment | periodic_segment (const Edge &e) const
| Same as the previous method for edge `e`.
Periodic_triangle | periodic_triangle (const Face_handle f) const
| Returns the periodic triangle formed by the three point-offset pairs corresponding to the three vertices of facet `f`.
Note that a traits class providing exact constructions should be used in order to guarantee the following operations to be exact (as opposed to computing the triangulation only, which requires only exact predicates).
Point | point (const Periodic_point &pp) const
| Converts the `Periodic_point` `pp` (point-offset pair) to the corresponding `Point` in \( \mathbb R^3\).
Segment | segment (const Periodic_segment &s) const
| Converts the `Periodic_segment` `s` to a `Segment`.
Triangle | triangle (const Periodic_triangle &t) const
| Converts the `Periodic_triangle` `this` to a `Triangle`.
Segment | segment (Face_handle f, int i) const
| Equivalent to the call `t.segment(t.periodic_segment(f,i));`
Segment | segment (const Edge &e) const
| Equivalent to the call `t.segment(t.periodic_segment(e));`
Segment | segment (const Edge_circulator &ec) const
| Equivalent to the call `t.segment(t.periodic_segment(ec->first, ec->second));`
Segment | segment (const Edge_iterator &ei) const
| Equivalent to the call `t.segment(t.periodic_segment(ei->first, ei->second));`
Triangle | triangle (Face_handle f) const
| Equivalent to the call `t.triangle(t.periodic_triangle(f));`

## Predicates
The class `Periodic_2_triangulation_2` provides methods to test the presence in the triangulation of a particular feature (edge or face).
bool | is_edge (Vertex_handle va, Vertex_handle vb)
| `true` if there is an edge having `va` and `vb` as vertices.
bool | is_edge (Vertex_handle va, Vertex_handle vb, Face_handle &fr, int &i)
| as above.
bool | is_face (Vertex_handle v1, Vertex_handle v2, Vertex_handle v3)
| `true` if there is a face having `v1`, `v2` and `v3` as vertices.
bool | is_face (Vertex_handle v1, Vertex_handle v2, Vertex_handle v3, Face_handle &fr)
| as above.

## Queries
The class `Periodic_2_triangulation_2` provides methods to locate a given point with respect to a triangulation. It also provides methods to locate a point with respect to a given face of the triangulation.
Face_handle | locate (const Point &query, Face_handle f=Face_handle()) const
| If the triangulation is not empty, a face that contains the query in its interior or on its boundary is returned.
Face_handle | locate (const Point &query, Locate_type &lt, int &li, Face_handle h=Face_handle()) const
| Same as above.
Oriented_side | oriented_side (Face_handle f, const Point &p) const
| Returns on which side of the oriented boundary of `f` the point `p` lies.

## Face, Edge and Vertex Iterators
The following iterators allow the user to visit faces, edges and vertices of the stored triangulation, i.e. in case of computing in a multiply sheeted covering space all stored periodic copies of each item are returned. These iterators are non-mutable, bidirectional and their value types are respectively `Face`, `Edge` and `Vertex`. They are all invalidated by any change in the triangulation.
Vertex_iterator | vertices_begin () const
| Starts at an arbitrary vertex.
Vertex_iterator | vertices_end () const
| Past-the-end iterator.
Edge_iterator | edges_begin () const
| Starts at an arbitrary edge.
Edge_iterator | edges_end () const
| Past-the-end iterator.
Face_iterator | faces_begin () const
| Starts at an arbitrary face.
Face_iterator | faces_end () const
| Past-the-end iterator.

## Geometric iterators
The following iterators allow the user to obtain geometric primitives corresponding to faces, edges, and vertices of the triangulation. These iterators are non-mutable, bidirectional and their value types are respectively `Periodic_triangle`, `Periodic_segment` and `Periodic_point`. They are all invalidated by any change in the triangulation. If the periodic triangulation is not computed in the 1-sheeted covering space, these iterators can be used to retain only the geometric primitives in the original domain. This can be controlled using the enum `Iterator_type`, see CGAL::Periodic_2_triangulation_2::Iterator_type. The four different modes of the geometric iterators: `STORED`, `STORED_COVER_DOMAIN`, `UNIQUE`, `UNIQUE_COVER_DOMAIN`. Note that in case of computing in the 1-sheeted covering space, stored and unique give the same result.
Periodic_point_iterator | periodic_points_begin (Iterator_type it=STORED) const
| Iterates over the points of the triangulation.
Periodic_point_iterator | periodic_points_end (Iterator_type it=STORED) const
| Past-the-end iterator.
Periodic_segment_iterator | periodic_segments_begin (Iterator_type it=STORED) const
| Iterates over the segments of the triangulation.
Periodic_segment_iterator | periodic_segments_end (Iterator_type it=STORED) const
| Past-the-end iterator.
Periodic_triangle_iterator | periodic_triangles_begin (Iterator_type it=STORED) const
| Iterates over the triangles of the triangulation.
Periodic_triangle_iterator | periodic_triangles_end (Iterator_type it=STORED) const
| Past-the-end iterator.

## Face, Edge and Vertex Circulators
The triangulation also provides circulators that allows to visit respectively all faces or edges incident to a given vertex or all vertices adjacent to a given vertex. These circulators are non-mutable and bidirectional. The `operator++` moves the circulator counterclockwise around the vertex while the `operator-` moves clockwise. A face circulator is invalidated by any modification of the face pointed to. An edge or a vertex circulator are invalidated by any modification of one of the two faces incident to the edge pointed to.
Face_circulator | incident_faces (Vertex_handle v) const
| Starts at an arbitrary face incident to `v`.
Face_circulator | incident_faces (Vertex_handle v, Face_handle f) const
| Starts at face `f`.
Edge_circulator | incident_edges (Vertex_handle v) const
| Starts at an arbitrary edge incident to `v`.
Edge_circulator | incident_edges (Vertex_handle v, Face_handle f) const
| Starts at the first edge of `f` incident to `v`, in counterclockwise order around `v`.
Vertex_circulator | adjacent_vertices (Vertex_handle v) const
| Starts at an arbitrary vertex adjacent to `v`.
Vertex_circulator | adjacent_vertices (Vertex_handle v, Face_handle f)
| Starts at the first vertex of `f` adjacent to `v` in counterclockwise order around `v`.

## Traversal between adjacent faces
Vertex_handle | mirror_vertex (Face_handle f, int i) const
| returns the vertex of the \( i^{th}\) neighbor of `f` that is opposite to `f`.
int | mirror_index (Face_handle f, int i) const
| returns the index of `f` in its \( i^{th}\) neighbor.
Insertion of a point on an edge. Insertion in a face. Advanced The following member functions offer more specialized versions of the insertion or removal operations to be used when one knows to be in the corresponding case. The following functions are mainly intended to be used in conjunction with the `find_conflicts()` member functions of Delaunay and constrained Delaunay triangulations to perform insertions.
Vertex_handle | insert_first (const Point &p)
| This is an advanced function.
Vertex_handle | insert_in_face (const Point &p, Face_handle f)
| This is an advanced function.
void | remove_degree_3 (Vertex_handle v)
| This is an advanced function.
void | remove_first (Vertex_handle v)
| This is an advanced function.
template<class EdgeIt >
Vertex_handle | star_hole (Point p, EdgeIt edge_begin, EdgeIt edge_end)
| This is an advanced function.
template<class EdgeIt , class FaceIt >
Vertex_handle | star_hole (Point p, EdgeIt edge_begin, EdgeIt edge_end, FaceIt face_begin, FaceIt face_end)
| This is an advanced function.
void | set_domain (const Iso_rectangle dom)
| This is an advanced function.

## Miscellaneous
int | ccw (int i) const
| Returns \( i+1\) modulo 3.
int | cw (int i) const
| Returns \( i+2\) modulo 3.
void | flippable (Face_handle f, int i)
size_t | degree (Vertex_handle v)
| Returns the degree of the vertex `v`

## Checking
Advanced The responsibility of keeping a valid triangulation belongs to the users if advanced operations are used. Obviously the advanced user, who implements higher levels operations may have to make a triangulation invalid at some times. The following method is provided to help the debugging.
bool | is_valid (bool verbose=false, int level=0) const
| This is an advanced function.

## Member Typedef Documentation

## ◆ Periodic_point

template<typename Traits , typename Tds >

typedef std::pair< Point, Offset > CGAL::Periodic_2_triangulation_2< Traits, Tds >::Periodic_point

represents a point-offset pair.

The point in the pair lies in the original domain.

## ◆ Unique_vertex_iterator

template<typename Traits , typename Tds >

typedef unspecified_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::Unique_vertex_iterator

iterator over the vertices whose corresponding points lie in the original domain, i.e.

for each set of periodic copies the `Unique_vertex_iterator` iterates over exactly one representative.

## Member Enumeration Documentation

## ◆ Iterator_type

template<typename Traits , typename Tds >

enum CGAL::Periodic_2_triangulation_2::Iterator_type

The enum Iterator_type is defined by `Periodic_2_triangulation_2` to specify the behavior of geometric iterators.

Enumerator
STORED | Return all geometric primitives as they are stored internally in `Triangulation_data_structure_2`.
UNIQUE | Return only one representative of each geometric primitive even if the triangulation is computed in a multiply sheeted covering space. Choose the representative whose maximum offset is minimal but non-negative in each direction of space.
STORED_COVER_DOMAIN | Same as `STORED` but return additionally all primitives whose intersection with the original domain of the current covering space is non-empty.
UNIQUE_COVER_DOMAIN | Same as `UNIQUE` but return additionally all primitives whose intersection with the original domain is non-empty.

## ◆ Locate_type

template<typename Traits , typename Tds >

enum CGAL::Periodic_2_triangulation_2::Locate_type

The enum `Locate_type` is defined by `Periodic_2_triangulation_2` to specify which case occurs when locating a point in the triangulation.

If the triangulation does not contain any points `EMPTY` is returned.

Enumerator
VERTEX | when the located point coincides with a vertex of the triangulation
EDGE | when the point is in the relative interior of an edge
FACE | when the point is in the interior of a facet
EMPTY | when the triangulation is empty

## Member Function Documentation

## ◆ adjacent_vertices()

template<typename Traits , typename Tds >

Vertex_circulator CGAL::Periodic_2_triangulation_2< Traits, Tds >::adjacent_vertices | ( | Vertex_handle | v,
|  | Face_handle | f
| ) |  |

Starts at the first vertex of `f` adjacent to `v` in counterclockwise order around `v`.

Precondition
  Face `f` is incident to vertex `v`.

## ◆ ccw()

template<typename Traits , typename Tds >

int CGAL::Periodic_2_triangulation_2< Traits, Tds >::ccw | ( | int | i | ) | const

Returns \( i+1\) modulo 3.

Precondition
  \(0 \leq i \leq 2\).

## ◆ convert_to_1_sheeted_covering()

template<typename Traits , typename Tds >

void CGAL::Periodic_2_triangulation_2< Traits, Tds >::convert_to_1_sheeted_covering | ( |  | ) |

This is an advanced function.

Advanced

Converts the current triangulation into the same periodic triangulation in the 1-sheeted covering space.

Precondition
  `is_triangulation_in_1_sheet()`

## ◆ convert_to_9_sheeted_covering()

template<typename Traits , typename Tds >

void CGAL::Periodic_2_triangulation_2< Traits, Tds >::convert_to_9_sheeted_covering | ( |  | ) |

This is an advanced function.

Advanced

Converts the current triangulation into the same periodic triangulation in the 9-sheeted covering space.

## ◆ cw()

template<typename Traits , typename Tds >

int CGAL::Periodic_2_triangulation_2< Traits, Tds >::cw | ( | int | i | ) | const

Returns \( i+2\) modulo 3.

Precondition
  \(0 \leq i \leq 2\).

## ◆ dimension()

template<typename Traits , typename Tds >

int CGAL::Periodic_2_triangulation_2< Traits, Tds >::dimension | ( |  | ) | const

Returns the dimension of the convex hull.

The dimension is zero if the triangulation is empty and two otherwise.

## ◆ incident_edges()

template<typename Traits , typename Tds >

Edge_circulator CGAL::Periodic_2_triangulation_2< Traits, Tds >::incident_edges | ( | Vertex_handle | v,
|  | Face_handle | f
| ) |  | const

Starts at the first edge of `f` incident to `v`, in counterclockwise order around `v`.

Precondition
  Face `f` is incident to vertex `v`.

## ◆ incident_faces()

template<typename Traits , typename Tds >

Face_circulator CGAL::Periodic_2_triangulation_2< Traits, Tds >::incident_faces | ( | Vertex_handle | v,
|  | Face_handle | f
| ) |  | const

Starts at face `f`.

Precondition
  Face `f` is incident to vertex `v`.

## ◆ insert_first()

template<typename Traits , typename Tds >

Vertex_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::insert_first | ( | const Point & | p | ) |

This is an advanced function.

Advanced

Inserts the first vertex.

## ◆ insert_in_face()

template<typename Traits , typename Tds >

Vertex_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::insert_in_face | ( | const Point & | p,
|  | Face_handle | f
| ) |  |

This is an advanced function.

Advanced

Inserts vertex `v` in face `f`. Face `f` is modified, two new faces are created. If the triangulation contains periodic copies, a point is inserted in all periodic copies.

Precondition
  The point in vertex `v` lies inside face `f`.

## ◆ is_edge()

template<typename Traits , typename Tds >

bool CGAL::Periodic_2_triangulation_2< Traits, Tds >::is_edge | ( | Vertex_handle | va,
|  | Vertex_handle | vb,
|  | Face_handle & | fr,
|  | int & | i
| ) |  |

as above.

In addition, if `true` is returned, the edge with vertices `va` and `vb` is the edge `e=(fr,i)` where `fr` is a handle to the face incident to `e` and on the right side of `e` oriented from `va` to `vb`.

## ◆ is_extensible_triangulation_in_1_sheet_h1()

template<typename Traits , typename Tds >

bool CGAL::Periodic_2_triangulation_2< Traits, Tds >::is_extensible_triangulation_in_1_sheet_h1 | ( |  | ) | const

This is an advanced function.

Advanced

The current triangulation remains a triangulation in the 1-sheeted covering space even after adding points if this method returns `true`. This test relies on a heuristic, i.e. if it answers `false` nothing is known. This test runs in constant-time when not computing in the 1-sheeted covering space. (This test uses the length of the longest edge in the triangulation as a criterion [1].)

## ◆ is_extensible_triangulation_in_1_sheet_h2()

template<typename Traits , typename Tds >

bool CGAL::Periodic_2_triangulation_2< Traits, Tds >::is_extensible_triangulation_in_1_sheet_h2 | ( |  | ) | const

This is an advanced function.

Advanced

The same as `is_extensible_triangulation_in_1_sheet_h1()` but with a more precise heuristic, i.e. it might answer `true` in cases in which `is_extensible_triangulation_in_1_sheet_h1()` would not. However, it is much less time efficient when not computing in the 1-sheeted covering space. (This test uses the diameter of the largest empty circle in the input point set as a criterion [1].)

## ◆ is_face()

template<typename Traits , typename Tds >

bool CGAL::Periodic_2_triangulation_2< Traits, Tds >::is_face | ( | Vertex_handle | v1,
|  | Vertex_handle | v2,
|  | Vertex_handle | v3,
|  | Face_handle & | fr
| ) |  |

as above.

In addition, if `true` is returned, `fr` is a handle to the face with `v1`, `v2` and `v3` as vertices.

## ◆ is_triangulation_in_1_sheet()

template<typename Traits , typename Tds >

bool CGAL::Periodic_2_triangulation_2< Traits, Tds >::is_triangulation_in_1_sheet | ( |  | ) | const

This is an advanced function.

Advanced

Returns `true` if the current triangulation would still be a triangulation in the 1-sheeted covering space, returns `false` otherwise.

## ◆ is_valid()

template<typename Traits , typename Tds >

bool CGAL::Periodic_2_triangulation_2< Traits, Tds >::is_valid | ( | bool | verbose = `false`,
|  | int | level = `0`
| ) |  | const

This is an advanced function.

Advanced

Checks the combinatorial validity of the triangulation and also the validity of its geometric embedding. This method is mainly a debugging help for the users of advanced features.

## ◆ locate() [1/2]

template<typename Traits , typename Tds >

Face_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::locate | ( | const Point & | query,
|  | Face_handle | f = `Face_handle()`
| ) |  | const

If the triangulation is not empty, a face that contains the query in its interior or on its boundary is returned.

If the triangulation is empty, the default constructed `Face_handle` is returned.

## ◆ locate() [2/2]

template<typename Traits , typename Tds >

Face_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::locate | ( | const Point & | query,
|  | Locate_type & | lt,
|  | int & | li,
|  | Face_handle | h = `Face_handle()`
| ) |  | const

Same as above.

Additionally, the parameters `lt` and `li` describe where the query point is located. The variable `lt` is set to the locate type of the query. If `lt==VERTEX` the variable `li` is set to the index of the vertex, and if `lt==EDGE` `li` is set to the index of the vertex opposite to the edge. Be careful that `li` has no meaning when the query type is `FACE` or when the triangulation is \( 0\)-dimensional.

## ◆ mirror_index()

template<typename Traits , typename Tds >

int CGAL::Periodic_2_triangulation_2< Traits, Tds >::mirror_index | ( | Face_handle | f,
|  | int | i
| ) |  | const

returns the index of `f` in its \( i^{th}\) neighbor.

Precondition
  \(0 \leq i \leq 2\).

## ◆ mirror_vertex()

template<typename Traits , typename Tds >

Vertex_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::mirror_vertex | ( | Face_handle | f,
|  | int | i
| ) |  | const

returns the vertex of the \( i^{th}\) neighbor of `f` that is opposite to `f`.

Precondition
  \( 0 \leq i \leq 2\).

## ◆ number_of_edges()

template<typename Traits , typename Tds >

size_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::number_of_edges | ( |  | ) | const

Returns the number of edges.

Counts all edges that are representatives of the same segment in \( \mathbb T_c^2\) as one edge.

## ◆ number_of_faces()

template<typename Traits , typename Tds >

size_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::number_of_faces | ( |  | ) | const

Returns the number of faces.

Counts all faces that are representatives of the same triangle in \( \mathbb T_c^2\) as one face.

## ◆ number_of_stored_edges()

template<typename Traits , typename Tds >

size_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::number_of_stored_edges | ( |  | ) | const

Returns the number of edges in the data structure.

This is the same as the number of sheets times `number_of_edges()`.

## ◆ number_of_stored_faces()

template<typename Traits , typename Tds >

size_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::number_of_stored_faces | ( |  | ) | const

Returns the number of faces in the data structure.

This is the same as the number of sheets times `number_of_faces()`.

## ◆ number_of_stored_vertices()

template<typename Traits , typename Tds >

size_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::number_of_stored_vertices | ( |  | ) | const

Returns the number of vertices in the data structure.

This is the same as the number of sheets times `number_of_vertices()`.

## ◆ number_of_vertices()

template<typename Traits , typename Tds >

size_type CGAL::Periodic_2_triangulation_2< Traits, Tds >::number_of_vertices | ( |  | ) | const

Returns the number of vertices.

Counts all vertices that are representatives of the same point in \( \mathbb T_c^2\) as one vertex.

## ◆ operator=()

template<typename Traits , typename Tds >

Triangulation_2 CGAL::Periodic_2_triangulation_2< Traits, Tds >::operator= | ( | const Triangulation_2< Traits, Tds > & | tr | ) |

Assignment.

All the vertices and faces are duplicated. After the assignment, `this` and `tr` refer to different triangulations: if `tr` is modified, `this` is not.

## ◆ periodic_point() [1/2]

template<typename Traits , typename Tds >

Periodic_point CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_point | ( | const Face_handle | f,
|  | int | i
| ) |  | const

If `this` is represented in the 1-sheeted covering space, this function returns the periodic point given by the \( i\)-th vertex of face `f`, that is the point in the original domain and the offset of the vertex in `f`.

If `this` is represented in the 9-sheeted covering space, this offset is possibly added to another offset determining the periodic copy.

Precondition
  \( i \in\{0,1,2\}\)

## ◆ periodic_point() [2/2]

template<typename Traits , typename Tds >

Periodic_point CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_point | ( | const Vertex_handle | v | ) | const

Returns the periodic point given by vertex `v`.

If `this` is represented in the 1-sheeted covering space, the offset is always zero. Otherwise `v` can correspond to a periodic copy outside the `domain` of an input point.

## ◆ periodic_points_begin()

template<typename Traits , typename Tds >

Periodic_point_iterator CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_points_begin | ( | Iterator_type | it = `STORED` | ) | const

Iterates over the points of the triangulation.

Its behavior is defined by the `Iterator_type` `it` as described on CGAL::Periodic_2_triangulation_2::Iterator_type.

## ◆ periodic_points_end()

template<typename Traits , typename Tds >

Periodic_point_iterator CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_points_end | ( | Iterator_type | it = `STORED` | ) | const

Past-the-end iterator.

Note that to match another `Periodic_point_iterator` both must have the same `Iterator_type` `it`.

## ◆ periodic_segment()

template<typename Traits , typename Tds >

Periodic_segment CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_segment | ( | const Face_handle | f,
|  | int | i
| ) |  | const

Returns the periodic segment formed by the two point-offset pairs corresponding to the two vertices of edge `(f,i)`.

Precondition
  \( i \in\{0,1,2\}\)

## ◆ periodic_segments_begin()

template<typename Traits , typename Tds >

Periodic_segment_iterator CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_segments_begin | ( | Iterator_type | it = `STORED` | ) | const

Iterates over the segments of the triangulation.

Its behavior is defined by the `Iterator_type` `it` as described on CGAL::Periodic_2_triangulation_2::Iterator_type.

## ◆ periodic_segments_end()

template<typename Traits , typename Tds >

Periodic_segment_iterator CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_segments_end | ( | Iterator_type | it = `STORED` | ) | const

Past-the-end iterator.

Note that to match another `Periodic_segment_iterator` both must have the same `Iterator_type` `it`.

## ◆ periodic_triangles_begin()

template<typename Traits , typename Tds >

Periodic_triangle_iterator CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_triangles_begin | ( | Iterator_type | it = `STORED` | ) | const

Iterates over the triangles of the triangulation.

Its behavior is defined by the `Iterator_type` `it` as described on CGAL::Periodic_2_triangulation_2::Iterator_type.

## ◆ periodic_triangles_end()

template<typename Traits , typename Tds >

Periodic_triangle_iterator CGAL::Periodic_2_triangulation_2< Traits, Tds >::periodic_triangles_end | ( | Iterator_type | it = `STORED` | ) | const

Past-the-end iterator.

Note that to match another `Periodic_triangle_iterator` both must have the same `Iterator_type` `it`.

## ◆ remove_degree_3()

template<typename Traits , typename Tds >

void CGAL::Periodic_2_triangulation_2< Traits, Tds >::remove_degree_3 | ( | Vertex_handle | v | ) |

This is an advanced function.

Advanced

Removes a vertex of degree three. Two of the incident faces are destroyed, the third one is modified.

Precondition
  Vertex `v` is a vertex with degree three.

## ◆ remove_first()

template<typename Traits , typename Tds >

void CGAL::Periodic_2_triangulation_2< Traits, Tds >::remove_first | ( | Vertex_handle | v | ) |

This is an advanced function.

Advanced

Removes the unique vertex in the triangulation.

## ◆ set_domain()

template<typename Traits , typename Tds >

void CGAL::Periodic_2_triangulation_2< Traits, Tds >::set_domain | ( | const Iso_rectangle | dom | ) |

This is an advanced function.

Advanced

Changes the domain. Note that this function calls `clear()`, i.e., it erases the existing triangulation.

## ◆ star_hole() [1/2]

template<typename Traits , typename Tds >
template<class EdgeIt >

Vertex_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::star_hole | ( | Point | p,
|  | EdgeIt | edge_begin,
|  | EdgeIt | edge_end
| ) |  |

This is an advanced function.

Advanced

creates a new vertex `v` and use it to star the hole whose boundary is described by the sequence of edges `[edge_begin, edge_end]`. Returns a handle to the new vertex.

Precondition
  The triangulation is a triangulation of 1 sheet

## ◆ star_hole() [2/2]

template<typename Traits , typename Tds >
template<class EdgeIt , class FaceIt >

Vertex_handle CGAL::Periodic_2_triangulation_2< Traits, Tds >::star_hole | ( | Point | p,
|  | EdgeIt | edge_begin,
|  | EdgeIt | edge_end,
|  | FaceIt | face_begin,
|  | FaceIt | face_end
| ) |  |

This is an advanced function.

Advanced

same as above, except that the algorithm first recycles faces in the sequence `[face_begin, face_end]` and create new ones only when the sequence is exhausted.

Precondition
  The triangulation is a triangulation of 1 sheet

## ◆ swap()

template<typename Traits , typename Tds >

void CGAL::Periodic_2_triangulation_2< Traits, Tds >::swap | ( | Triangulation_2 & | tr | ) |

The triangulations `tr` and `this` are swapped.

`t.swap(tr)` should be preferred to `this` = `tr` or to `t(tr)` if `tr` is deleted after that.

## ◆ tds()

template<typename Traits , typename Tds >

Triangulation_data_structure_2 & CGAL::Periodic_2_triangulation_2< Traits, Tds >::tds | ( |  | ) |

This is an advanced function.

Advanced

Returns a reference to the triangulation data structure.

## ◆ Triangulation_2() [1/2]

template<typename Traits , typename Tds >

CGAL::Periodic_2_triangulation_2< Traits, Tds >::Triangulation_2 | ( | const Iso_rectangle & | domain = `Iso_rectangle(0, 0, 1, 1)`,
|  | const Geom_traits & | traits = `Geom_traits()`
| ) |  |

Introduces an empty triangulation `t` with `domain` as original domain.

Precondition
  `domain` is a square.

## ◆ Triangulation_2() [2/2]

template<typename Traits , typename Tds >

CGAL::Periodic_2_triangulation_2< Traits, Tds >::Triangulation_2 | ( | const Triangulation_2 & | tr | ) |

Copy constructor.

All the vertices and faces are duplicated. After the copy, `this` and `tr` refer to different triangulations: if `tr` is modified, `this` is not.

## Friends And Related Function Documentation

## ◆ operator<<()

template<typename Traits , typename Tds >

ostream & operator<< | ( | ostream & | os,
|  | const Periodic_2_triangulation_2< Traits, Tds > & | t
| ) |  |
| related

Writes the triangulation `t` into the stream `os`.

Precondition
  The output operator must be defined for `Point`.

## ◆ operator>>()

template<typename Traits , typename Tds >

istream & operator>> | ( | istream & | is,
|  | Triangulation_2< Traits, Tds > & | t
| ) |  |
| related

Reads a triangulation from stream `is` and assigns it to `t`.

Precondition
  The input operator must be defined for `Point`.