CGAL 4.7 - 2D Triangulation
CGAL::Regular_triangulation_2< Traits, Tds > Class Template Reference

#include <CGAL/Regular_triangulation_2.h>

## Definition

The class Regular_triangulation_2 is designed to maintain the regular triangulation of a set of weighted points.

Let $${ PW} = \{(p_i, w_i), i = 1, \ldots , n \}$$ be a set of weighted points where each $$p_i$$ is a point and each $$w_i$$ is a scalar called the weight of point $$p_i$$. Alternatively, each weighted point $$(p_i, w_i)$$ can be regarded as a two dimensional sphere with center $$p_i$$ and radius $$r_i=\sqrt{w_i}$$.

The power diagram of the set $${ PW}$$ is a planar partition such that each cell corresponds to sphere $$(p_i, w_i)$$ of $${ PW}$$ and is the locus of points $$p$$ whose power with respect to $$(p_i, w_i)$$ is less than its power with respect to any other sphere $$(p_j, w_j)$$ in $${ PW}$$. The dual of this diagram is a triangulation whose domain covers the convex hull of the set $${ P}= \{ p_i, i = 1, \ldots , n \}$$ of center points and whose vertices are a subset of $${ P}$$. Such a triangulation is called a regular triangulation. The three points $$p_i, p_j$$ and $$p_k$$ of $${ P}$$ form a triangle in the regular triangulation of $${ PW}$$ iff there is a point $$p$$ of the plane whose powers with respect to $$(p_i, w_i)$$, $$(p_j, w_j)$$ and $$(p_k, w_k)$$ are equal and less than the power of $$p$$ with respect to any other sphere in $${ PW}$$.

Let us defined the power product of two weighted points $$(p_i, w_i)$$ and $$(p_j, w_j)$$ as:

$\Pi(p_i, w_i,p_j, w_j) = p_ip_j ^2 - w_i - w_j .$

$$\Pi(p_i, w_i,p_j, 0)$$ is simply the power of point $$p_j$$ with respect to the sphere $$(p_i, w_i)$$, and two weighted points are said to be orthogonal if their power product is null. The power circle of three weighted points $$(p_i, w_i)$$, $$(p_j, w_j)$$ and $$(p_k, w_k)$$ is defined as the unique circle $$(\pi, \omega)$$ orthogonal to $$(p_i, w_i)$$, $$(p_j, w_j)$$ and $$(p_k, w_k)$$.

The regular triangulation of the sets $${ PW}$$ satisfies the following regular property (which just reduces to the Delaunay property when all the weights are null): a triangle $$p_ip_jp_k$$ of the regular triangulation of $${ PW}$$ is such that the power product of any weighted point $$(p_l, w_l)$$ of $${ PW}$$ with the power circle of $$(p_i, w_i)$$, $$(p_j, w_j)$$ is $$(p_k, w_k)$$ is positive or null. We call power test of the weighted point $$(p_l, w_l)$$ with respect to the face $$p_ip_jp_k$$, the predicates testing the sign of the power product of $$(p_l, w_l)$$ with respect to the power circle of $$(p_i, w_i)$$, $$(p_j, w_j)$$ is $$(p_k, w_k)$$. This power product is given by the following determinant

$\left| \begin{array}{cccc} 1 & x_i & y_i & x_i ^2 + y_i ^2 - w_i \\ 1 & x_j & y_j & x_j ^2 + y_j ^2 - w_j \\ 1 & x_k & y_k & x_k ^2 + y_k ^2 - w_k \\ 1 & x_l & y_l & x_l ^2 + y_l ^2 - w_l \end{array} \right|$

A pair of neighboring faces $$p_ip_jp_k$$ and $$p_ip_jp_l$$ is said to be locally regular (with respect to the weights in $${ PW}$$) if the power test of $$(p_l,w_l)$$ with respect to $$p_ip_jp_k$$ is positive. A classical result of computational geometry establishes that a triangulation of the convex hull of $${ P}$$ such that any pair of neighboring faces is regular with respect to $${ PW}$$, is a regular triangulation of $${ PW}$$.

Alternatively, the regular triangulation of the weighted points set $${ PW}$$ can be obtained as the projection on the two dimensional plane of the convex hull of the set of three dimensional points $${ P'}= \{ (p_i,p_i ^2 - w_i ), i = 1, \ldots , n \}$$.

The vertices of the regular triangulation of a set of weighted points $${ PW}$$ form only a subset of the set of center points of $${ PW}$$. Therefore the insertion of a weighted point in a regular triangulation does not necessarily imply the creation of a new vertex. If the new inserted point does not appear as a vertex in the regular triangulation, it is said to be hidden.

Hidden points are stored in special vertices called hidden vertices. A hidden point is considered as hidden by the facet of the triangulation where its point component is located : in fact, the hidden point can appear as vertex of the triangulation only if this facet is removed. Each face of a regular triangulation stores the list of hidden vertices whose points are located in the facet. When a facet is removed, points hidden by this facet are reinserted in the triangulation.

Template Parameters
 Traits is the geometric traits parameter and must be a model of the concept RegularTriangulationTraits_2. The concept RegularTriangulationTraits_2 refines the concept TriangulationTraits_2 by adding the type Weighted_point_2 to describe weighted points and the type Power_test_2 to perform power tests on weighted points. Tds must be a model of TriangulationDataStructure_2. The face base of a regular triangulation has to be a model of the concept RegularTriangulationFaceBase_2. while the vertex base class has to be a model of RegularTriangulationVertexBase_2. CGAL provides a default instantiation for the Tds parameter by the class Triangulation_data_structure_2 < Regular_triangulation_vertex_base_2, Regular_triangulation_face_base_2 >.
CGAL::Triangulation_2<Traits,Tds>
TriangulationDataStructure_2
RegularTriangulationTraits_2
RegularTriangulationFaceBase_2
RegularTriangulationVertexBase_2
CGAL::Regular_triangulation_face_base_2<Traits>
CGAL::Regular_triangulation_vertex_base_2<Traits>
Examples:
Triangulation_2/info_insert_with_pair_iterator_regular_2.cpp, and Triangulation_2/regular.cpp.

## Types

typedef Traits::Distance Distance

typedef Traits::Line Line

typedef Traits::Ray Ray

typedef Traits::Bare_point Bare_point

typedef Traits::Weighted_point Weighted_point

typedef unspecified_type All_vertices_iterator
An iterator that allows to enumerate the vertices that are not hidden.

typedef unspecified_type Finite_vertices_iterator
An iterator that allows to enumerate the finite vertices that are not hidden.

typedef unspecified_type Hidden_vertices_iterator
An iterator that allows to enumerate the hidden vertices.

## Creation

Regular_triangulation_2 (const Traits &gt=Traits())
Introduces an empty regular triangulation.

Regular_triangulation_2 (const Regular_triangulation_2 &rt)
Copy constructor.

template<class InputIterator >
Regular_triangulation_2
< Traits, Tds >
Regular_triangulation_2 (InputIterator first, InputIterator last, Traits gt=Traits())
Equivalent to constructing an empty triangulation with the optional traits class argument and calling insert(first,last).

## Insertion and Removal

Vertex_handle insert (const Weighted_point &p, Face_handle f=Face_handle())
inserts weighted point p in the regular triangulation. More...

Vertex_handle insert (const Weighted_point &p, Locate_type lt, Face_handle loc, int li)
insert a weighted point p whose bare-point is assumed to be located in lt,loc,li. More...

Vertex_handle push_back (const Point &p)
Equivalent to insert(p).

template<class InputIterator >
std::ptrdiff_t insert (InputIterator first, InputIterator last)
inserts the weighted points in the range [first,last). More...

template<class WeightedPointWithInfoInputIterator >
std::ptrdiff_t insert (WeightedPointWithInfoInputIterator first, WeightedPointWithInfoInputIterator last)
inserts the weighted points in the range [first,last). More...

void remove (Vertex_handle v)
removes the vertex from the triangulation.

## Queries

template<class OutputItFaces , class OutputItBoundaryEdges , class OutputItHiddenVertices >
CGAL::Triple< OutputItFaces,
OutputItBoundaryEdges,
OutputItHiddenVertices >
get_conflicts_and_boundary_and_hidden_vertices (const Weighted_point &p, OutputItFaces fit, OutputItBoundaryEdges eit, OutputItHiddenVertices vit, Face_handle start) const
outputs the faces, boundary edges, and hidden vertices of the conflict zone of point p to output iterators. More...

template<class OutputItFaces , class OutputItBoundaryEdges >
std::pair< OutputItFaces,
OutputItBoundaryEdges >
get_conflicts_and_boundary (const Weighted_point &p, OutputItFaces fit, OutputItBoundaryEdges eit, Face_handle start) const
outputs the faces and boundary edges of the conflict zone of point p to output iterators. More...

template<class OutputItFaces , class OutputItHiddenVertices >
std::pair< OutputItFaces,
OutputItHiddenVertices >
get_conflicts_and_hidden_vertices (const Weighted_point &p, OutputItFaces fit, OutputItHiddenVertices vit, Face_handle start) const
outputs the faces and hidden vertices of the conflict zone of point p to output iterators. More...

template<class OutputItBoundaryEdges , class OutputItHiddenVertices >
std::pair
< OutputItBoundaryEdges,
OutputItHiddenVertices >
get_boundary_of_conflicts_and_hidden_vertices (const Weighted_point &p, OutputItBoundaryEdges eit, OutputItHiddenVertices vit, Face_handle start) const
outputs the boundary edges and hidden vertices of the conflict zone of point p to output iterators. More...

template<class OutputItFaces >
OutputItFaces get_conflicts (const Point &p, OutputItFaces fit, Face_handle start) const
outputs the faces of the conflict zone of point p to output iterators. More...

template<class OutputItBoundaryEdges >
OutputItBoundaryEdges get_boundary_of_conflicts (const Point &p, OutputItBoundaryEdges eit, Face_handle start) const
outputs the boundary edges of the conflict zone of p in counterclockwise order where each edge is described through the incident face which is not in conflict with p. More...

template<class OutputItHiddenVertices >
OutputItHiddenVertices get_hidden_vertices (const Point &p, OutputItHiddenVertices vit, Face_handle start) const
outputs the hidden vertices of the conflict zone of p into an output iterator. More...

Vertex_handle nearest_power_vertex (Bare_point p) const
Returns the vertex of the triangulation which is nearest to p with respect to the power distance. More...

## Access Functions

int number_of_vertices () const
returns the number of finite vertices that are not hidden.

int number_of_hidden_vertices () const
returns the number of hidden vertices.

Hidden_vertices_iterator hidden_vertices_begin () const
starts at an arbitrary hidden vertex.

Hidden_vertices_iterator hidden_vertices_end () const
past the end iterator for the sequence of hidden vertices.

Finite_vertices_iterator finite_vertices_begin () const
starts at an arbitrary unhidden finite vertex

Finite_vertices_iterator finite_vertices_end () const
Past-the-end iterator.

All_vertices_iterator all_vertices_end () const
starts at an arbitrary unhidden vertex.

All_vertices_iterator all_vertices_begin () const
past the end iterator.

## Dual Power Diagram

The following member functions provide the elements of the dual power diagram.

Point weighted_circumcenter (const Face_handle &f) const
returns the center of the circle orthogonal to the three weighted points corresponding to the vertices of face f. More...

Point dual (const Face_handle &f) const
same as weighted_circumcenter.

Object dual (const Edge &e) const
If both incident faces are finite, returns a segment whose endpoints are the duals of each incident face. More...

Object dual (const Edge_circulator &ec) const
Idem.

Object dual (const Edge_iterator &ei) const
Idem.

template<class Stream >
Stream & draw_dual (Stream &ps)
output the dual power diagram to stream ps.

## Predicates

Oriented_side power_test (Face_handle f, const Weighted_point &p) const
Returns the power test of p with respect to the power circle associated with f.

## Miscellaneous

bool is_valid (bool verbose=false, int level=0) const
Tests the validity of the triangulation as a Triangulation_2 and additionally test the regularity of the triangulation. More...

Public Member Functions inherited from CGAL::Triangulation_cw_ccw_2
Triangulation_cw_ccw_2 ()
default constructor.

int ccw (const int i) const
returns the index of the neighbor or vertex that is next to the neighbor or vertex with index i in counterclockwise order around a face.

int cw (const int i) const
returns the index of the neighbor or vertex that is next to the neighbor or vertex with index i in counterclockwise order around a face.

## Member Function Documentation

template<typename Traits , typename Tds >
 Object CGAL::Regular_triangulation_2< Traits, Tds >::dual ( const Edge & e) const

If both incident faces are finite, returns a segment whose endpoints are the duals of each incident face.

If only one incident face is finite, returns a ray whose endpoint is the dual of the finite incident face and supported by the line which is the bisector of the edge's endpoints. If both incident faces are infinite, returns the line which is the bisector of the edge's endpoints otherwise.

template<typename Traits , typename Tds >
template<class OutputItBoundaryEdges >
 OutputItBoundaryEdges CGAL::Regular_triangulation_2< Traits, Tds >::get_boundary_of_conflicts ( const Point & p, OutputItBoundaryEdges eit, Face_handle start ) const

outputs the boundary edges of the conflict zone of p in counterclockwise order where each edge is described through the incident face which is not in conflict with p.

The function returns the resulting output iterator.

template<typename Traits , typename Tds >
template<class OutputItBoundaryEdges , class OutputItHiddenVertices >
 std::pair CGAL::Regular_triangulation_2< Traits, Tds >::get_boundary_of_conflicts_and_hidden_vertices ( const Weighted_point & p, OutputItBoundaryEdges eit, OutputItHiddenVertices vit, Face_handle start ) const

outputs the boundary edges and hidden vertices of the conflict zone of point p to output iterators.

See get_conflicts_and_boundary_and_hidden_vertices() for details. The function returns in a std::pair the resulting output iterators.

template<typename Traits , typename Tds >
template<class OutputItFaces >
 OutputItFaces CGAL::Regular_triangulation_2< Traits, Tds >::get_conflicts ( const Point & p, OutputItFaces fit, Face_handle start ) const

outputs the faces of the conflict zone of point p to output iterators.

The function returns the resulting output iterator.

Precondition
dimension()==2.
template<typename Traits , typename Tds >
template<class OutputItFaces , class OutputItBoundaryEdges >
 std::pair CGAL::Regular_triangulation_2< Traits, Tds >::get_conflicts_and_boundary ( const Weighted_point & p, OutputItFaces fit, OutputItBoundaryEdges eit, Face_handle start ) const

outputs the faces and boundary edges of the conflict zone of point p to output iterators.

See get_conflicts_and_boundary_and_hidden_vertices() for details.

The function returns in a std::pair the resulting output iterators.

Precondition
dimension()==2.
template<typename Traits , typename Tds >
template<class OutputItFaces , class OutputItBoundaryEdges , class OutputItHiddenVertices >
 CGAL::Triple CGAL::Regular_triangulation_2< Traits, Tds >::get_conflicts_and_boundary_and_hidden_vertices ( const Weighted_point & p, OutputItFaces fit, OutputItBoundaryEdges eit, OutputItHiddenVertices vit, Face_handle start ) const

outputs the faces, boundary edges, and hidden vertices of the conflict zone of point p to output iterators.

Template Parameters
 OutputItFaces is an output iterator with Face_handle as value type. OutputItBoundaryEdges is an output iterator with Edge as value type. OutputItHiddenVertices is an output iterator with Vertex_handle as value type.

This member function outputs in the container pointed to by fit the faces which are in conflict with point p, i.e., the faces whose power circles have negative power wrt. p. It outputs in the container pointed to by eit the boundary of the zone in conflict with p. It inserts the vertices that would be hidden by p into the container pointed to by vit. The boundary edges of the conflict zone are output in counter-clockwise order and each edge is described through its incident face which is not in conflict with p. The function returns in a CGAL::Triple the resulting output iterators.

Precondition
dimension()==2.
template<typename Traits , typename Tds >
template<class OutputItFaces , class OutputItHiddenVertices >
 std::pair CGAL::Regular_triangulation_2< Traits, Tds >::get_conflicts_and_hidden_vertices ( const Weighted_point & p, OutputItFaces fit, OutputItHiddenVertices vit, Face_handle start ) const

outputs the faces and hidden vertices of the conflict zone of point p to output iterators.

See get_conflicts_and_boundary_and_hidden_vertices() for details. The function returns in a std::pair the resulting output iterators.

Precondition
dimension()==2.
template<typename Traits , typename Tds >
template<class OutputItHiddenVertices >
 OutputItHiddenVertices CGAL::Regular_triangulation_2< Traits, Tds >::get_hidden_vertices ( const Point & p, OutputItHiddenVertices vit, Face_handle start ) const

outputs the hidden vertices of the conflict zone of p into an output iterator.

The function returns the resulting output iterator.

template<typename Traits , typename Tds >
 Vertex_handle CGAL::Regular_triangulation_2< Traits, Tds >::insert ( const Weighted_point & p, Face_handle f = Face_handle() )

inserts weighted point p in the regular triangulation.

If the point p does not appear as a vertex of the triangulation, the returned vertex is a hidden vertex. If given the parameter f is used as an hint for the place to start the location process of point p.

template<typename Traits , typename Tds >
 Vertex_handle CGAL::Regular_triangulation_2< Traits, Tds >::insert ( const Weighted_point & p, Locate_type lt, Face_handle loc, int li )

insert a weighted point p whose bare-point is assumed to be located in lt,loc,li.

See the description of member function Triangulation_2::locate().

template<typename Traits , typename Tds >
template<class InputIterator >
 std::ptrdiff_t CGAL::Regular_triangulation_2< Traits, Tds >::insert ( InputIterator first, InputIterator last )

inserts the weighted points in the range [first,last).

It returns the difference of the number of vertices between after and before the insertions (it may be negative due to hidden points). Note that this function is not guaranteed to insert the weighted points following the order of InputIterator, as spatial_sort() is used to improve efficiency.

Template Parameters
 InputIterator must be an input iterator with the value type Weighted_point.
template<typename Traits , typename Tds >
template<class WeightedPointWithInfoInputIterator >
 std::ptrdiff_t CGAL::Regular_triangulation_2< Traits, Tds >::insert ( WeightedPointWithInfoInputIterator first, WeightedPointWithInfoInputIterator last )

inserts the weighted points in the range [first,last).

It returns the difference of the number of vertices between after and before the insertions (it may be negative due to hidden points). Note that this function is not guaranteed to insert the weighted points following the order of WeightedPointWithInfoInputIterator, as spatial_sort is used to improve efficiency. Given a pair (p,i), the vertex v storing p also stores i, that is v.point() == p and v.info() == i. If several pairs have the same point, only one vertex is created, one of the objects of type Vertex::Info will be stored in the vertex.

Precondition
Vertex must be model of the concept TriangulationVertexBaseWithInfo_2.
Template Parameters
 WeightedPointWithInfoInputIterator must be an input iterator with value type std::pair.
template<typename Traits , typename Tds >
 bool CGAL::Regular_triangulation_2< Traits, Tds >::is_valid ( bool verbose = false, int level = 0 ) const

Tests the validity of the triangulation as a Triangulation_2 and additionally test the regularity of the triangulation.

This method is useful to debug regular triangulation algorithms implemented by the user.

template<typename Traits , typename Tds >
 Vertex_handle CGAL::Regular_triangulation_2< Traits, Tds >::nearest_power_vertex ( Bare_point p) const

Returns the vertex of the triangulation which is nearest to p with respect to the power distance.

This means that the power of the query point p with respect to the weighted point in the nearest vertex is smaller than the power of p with respect to the weighted point in any other vertex. Ties are broken arbitrarily. The default constructed handle is returned if the triangulation is empty.

template<typename Traits , typename Tds >
 Point CGAL::Regular_triangulation_2< Traits, Tds >::weighted_circumcenter ( const Face_handle & f) const

returns the center of the circle orthogonal to the three weighted points corresponding to the vertices of face f.

Precondition
f is not infinite.