\( \newcommand{\E}{\mathrm{E}} \) \( \newcommand{\A}{\mathrm{A}} \) \( \newcommand{\R}{\mathrm{R}} \) \( \newcommand{\N}{\mathrm{N}} \) \( \newcommand{\Q}{\mathrm{Q}} \) \( \newcommand{\Z}{\mathrm{Z}} \) \( \def\ccSum #1#2#3{ \sum_{#1}^{#2}{#3} } \def\ccProd #1#2#3{ \sum_{#1}^{#2}{#3} }\)
CGAL 4.9 - 3D Polyhedral Surface
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CGAL::Polyhedron_3< Traits >::Halfedge Class Reference

#include <CGAL/Polyhedron_3.h>

Definition

A halfedge is an oriented edge between two vertices.

It is always paired with a halfedge pointing in the opposite direction. The Halfedge::opposite() member function returns this halfedge of opposite orientation. If a halfedge is incident to a facet the Halfedge::next() member function points to the successor halfedge around this facet. For border edges the Halfedge::next() member function points to the successor halfedge along the hole. For more than two border edges at a vertex, the next halfedge along a hole is not uniquely defined, but a consistent assignment of the next halfedge will be maintained in the data structure. An invariant is that successive assignments of the form h = h->next() cycle counterclockwise around the facet (or hole) and traverse all halfedges incident to this facet (or hole). A similar invariant is that successive assignments of the form h = h->next()->opposite() cycle clockwise around the vertex and traverse all halfedges incident to this vertex. Two circulators are provided for these circular orders.

poly_optional.png
The three classes Vertex, Halfedge, and Facet of the polyhedral surface. Member functions with shaded background are mandatory. The others are optionally supported.

The incidences encoded in Halfedge::opposite() and Halfedge::next() are available for each instantiation of polyhedral surfaces. The other incidences are optionally available as indicated with type tags. The Halfedge::prev() member function points to the preceding halfedge around the same facet. It is always available, though it might perform a search around the facet using the Halfedge::next() member function to find the previous halfedge if the underlying halfedge data structure does not provide an efficient Halfedge::prev() member function for halfedges. Handles to the incident vertex and facet are optionally stored.

The circulators are assignable to the Halfedge_handle. The circulators are bidirectional if the halfedge provided to the polyhedron with the Items template argument provides a member function Halfedge::prev(), otherwise they are of the forward category.

See Also
CGAL::Polyhedron_3::Vertex
CGAL::Polyhedron_3::Facet
CGAL::Polyhedron_3<Traits>

Implementation

The member functions Halfedge::prev() and Halfedge::prev_on_vertex() work in constant time if Supports_halfedge_prev \( \equiv\) CGAL::Tag_true. Otherwise both methods search for the previous halfedge around the incident facet.

Types

typedef unspecified_type Vertex
 type of incident vertices.
 
typedef unspecified_type Facet
 type of incident facets.
 
typedef unspecified_type Vertex_handle
 handle to vertex.
 
typedef unspecified_type Halfedge_handle
 handle to halfedge.
 
typedef unspecified_type Facet_handle
 handle to facet.
 
typedef unspecified_type Halfedge_around_vertex_circulator
 circulator of halfedges around a vertex.
 
typedef unspecified_type Halfedge_around_facet_circulator
 circulator of halfedges around a facet.
 
typedef unspecified_type Vertex_const_handle
 
typedef unspecified_type Halfedge_const_handle
 
typedef unspecified_type Facet_const_handle
 
typedef unspecified_type Halfedge_around_vertex_const_circulator
 
typedef unspecified_type Halfedge_around_facet_const_circulator
 
typedef unspecified_type Supports_halfedge_prev
 \( \equiv\) CGAL::Tag_true or CGAL::Tag_false.
 
typedef unspecified_type Supports_halfedge_vertex
 \( \equiv\) CGAL::Tag_true or CGAL::Tag_false.
 
typedef unspecified_type Supports_halfedge_face
 \( \equiv\) CGAL::Tag_true or CGAL::Tag_false.
 

Creation

 Halfedge ()
 default constructor.
 

Operations

Halfedge_handle opposite ()
 
Halfedge_const_handle opposite () const
 the opposite halfedge.
 
Halfedge_handle next ()
 
Halfedge_const_handle next () const
 the next halfedge around the facet.
 
Halfedge_handle prev ()
 
Halfedge_const_handle prev () const
 the previous halfedge around the facet.
 
Halfedge_handle next_on_vertex ()
 
Halfedge_const_handle next_on_vertex () const
 the next halfedge around the vertex (clockwise). More...
 
Halfedge_handle prev_on_vertex ()
 
Halfedge_const_handle prev_on_vertex () const
 the previous halfedge around the vertex (counterclockwise). More...
 
bool is_border () const
 is true if h is a border halfedge.
 
bool is_border_edge () const
 is true if this or the opposite halfedge is a border halfedge.
 
Halfedge_around_vertex_circulator vertex_begin ()
 
Halfedge_around_vertex_const_circulator vertex_begin () const
 circulator of halfedges around the vertex (clockwise), the vertex of the halfedges being *this.
 
Halfedge_around_facet_circulator facet_begin ()
 
Halfedge_around_facet_const_circulator facet_begin () const
 circulator of halfedges around the facet (counterclockwise).
 
std::size_t vertex_degree () const
 the degree of the incident vertex, i.e., number of edges emanating from this vertex.
 
bool is_bivalent () const
 returns true if the incident vertex has exactly two incident edges.
 
bool is_trivalent () const
 returns true if the incident vertex has exactly three incident edges.
 
std::size_t facet_degree () const
 the degree of the incident facet, i.e., number of edges on the boundary of this facet.
 
bool is_triangle () const
 returns true if the incident facet is a triangle.
 
bool is_quad () const
 returns true if the incident facet is a quadrilateral.
 

Operations available if Supports_halfedge_vertex is CGAL::Tag_true

Vertex_handle vertex ()
 
Vertex_const_handle vertex () const
 the incident vertex of the halfedge.
 

Operations available if Supports_halfedge_facet is CGAL::Tag_true

Facet_handle facet ()
 
Facet_const_handle facet () const
 the incident facet of the halfedge. More...
 

Member Function Documentation

template<typename Traits >
Facet_const_handle CGAL::Polyhedron_3< Traits >::Halfedge::facet ( ) const

the incident facet of the halfedge.

If the hafedge is a border halfedge the result is default construction of the handle.

template<typename Traits >
Halfedge_const_handle CGAL::Polyhedron_3< Traits >::Halfedge::next_on_vertex ( ) const

the next halfedge around the vertex (clockwise).

Is equal to h.next()->opposite().

template<typename Traits >
Halfedge_const_handle CGAL::Polyhedron_3< Traits >::Halfedge::prev_on_vertex ( ) const

the previous halfedge around the vertex (counterclockwise).

Is equal to h.opposite()->prev().