 CGAL 5.1.3 - 2D Boolean Operations on Nef Polygons
CGAL::Nef_polyhedron_2< T >::Topological_explorer Class Reference

#include <CGAL/Nef_polyhedron_2.h>

Inherited by CGAL::Nef_polyhedron_2< T >::Explorer.

## Definition

An instance D of the data type Topological_explorer is a decorator for interfacing the topological structure of a plane map P (read-only).

A plane map P consists of a triple $$(V, E, F)$$ of vertices, edges, and faces. We collectively call them objects. An edge e is a pair of vertices (v,w) with incidence operations v = source(e), w = target(e). The list of all edges with source v is called the adjacency list A(v).

Edges are paired into twins. For each edge e = (v,w) there's an edge twin(e) = (w,v) and twin(twin(e)) == eThe existence of the edge pairs makes P a bidirected graph, the twin links make P a map..

An edge e = (v,w) knows two adjacent edges en = next(e) and ep = previous(e) where source(en) = w, previous(en) = e and target(ep) = v and next(ep) = e. By this symmetric previous-next relationship all edges are partitioned into face cycles. Two edges $$e$$ and $$e'$$ are in the same face cycle if $$e = next^*(e')$$. All edges e in the same face cycle have the same incident face $$f = face(e)$$. The cyclic order on the adjacency list of a vertex v = source(e) is given by cyclic_adj_succ(e) = twin(previous(e)) and cyclic_adj_pred(e) = next(twin(e)).

A vertex v is embedded via coordinates point(v). By the embedding of its source and target an edge corresponds to a segment. P has the property that the embedding is always order-preserving. This means a ray fixed in point(v) of a vertex v and swept around counterclockwise meets the embeddings of target(e) ( $$e \in A(v)$$) in the cyclic order defined by the list order of A.

The embedded face cycles partition the plane into maximal connected subsets of points. Each such set corresponds to a face. A face is bounded by its incident face cycles. For all the edges in the non-trivial face cycles it holds that the face is left of the edges. There can also be trivial face cycles in form of isolated vertices in the interior of a face. Each such vertex v knows its surrounding face f = face(v).

Plane maps are attributed, for each object $$u \in V \cup E \cup F$$ we attribute an information mark(u) of type Mark. Mark fits the concepts assignable, default-constructible, and equal-comparable.

## Types

typedef unspecified_type Plane_map
The underlying plane map type.

typedef unspecified_type Point
The point type of vertices.

typedef unspecified_type Mark
All objects (vertices, edges, faces) are attributed by a Mark object.

typedef unspecified_type Size_type
The size type.

## Circulators

Local types are handles, iterators and circulators of the following kind: Vertex_const_handle, Vertex_const_iterator, Halfedge_const_handle, Halfedge_const_iterator, Face_const_handle, Face_const_iterator.

Additionally the following circulators are defined.

typedef unspecified_type Halfedge_around_vertex_const_circulator
circulating the outgoing halfedges in $$A(v)$$.

typedef unspecified_type Halfedge_around_face_const_circulator
circulating the halfedges in the face cycle of a face f.

typedef unspecified_type Hole_const_iterator
iterating all holes of a face f. More...

typedef unspecified_type Isolated_vertex_const_iterator
iterating all isolated vertices of a face f. More...

## Operations

Vertex_const_handle source (Halfedge_const_handle e)
returns the source of e.

Vertex_const_handle target (Halfedge_const_handle e)
returns the target of e.

Halfedge_const_handle twin (Halfedge_const_handle e)
returns the twin of e.

bool is_isolated (Vertex_const_handle v)
returns true iff $$A(v) = \emptyset$$.

Halfedge_const_handle first_out_edge (Vertex_const_handle v)
returns one halfedge with source v. More...

Halfedge_const_handle last_out_edge (Vertex_const_handle v)
returns the halfedge with source v that is the last in the circular iteration before encountering first_out_edge(v) again. More...

returns the edge after e in the cyclic ordered adjacency list of source(e).

returns the edge before e in the cyclic ordered adjacency list of source(e).

Halfedge_const_handle next (Halfedge_const_handle e)
returns the next edge in the face cycle containing e.

Halfedge_const_handle previous (Halfedge_const_handle e)
returns the previous edge in the face cycle containing e.

Face_const_handle face (Halfedge_const_handle e)
returns the face incident to e.

Face_const_handle face (Vertex_const_handle v)
returns the face incident to v. More...

Halfedge_const_handle halfedge (Face_const_handle f)
returns a halfedge in the bounding face cycle of f (Halfedge_const_handle() if there is no bounding face cycle).

## Iteration

Vertex_const_iterator vertices_begin ()
iterator over vertices of the map.

Vertex_const_iterator vertices_end ()
past-the-end iterator for vertices.

Halfedge_const_iterator halfedges_begin ()
iterator over halfedges of the map.

Halfedge_const_iterator halfedges_end ()
past-the-end iterator for halfedges.

Face_const_iterator faces_begin ()
iterator over faces of the map.

Face_const_iterator faces_end ()
past-the-end iterator for faces

Halfedge_around_vertex_const_circulator out_edges (Vertex_const_handle v)
returns a circulator for the cyclic adjacency list of v.

Halfedge_around_face_const_circulator face_cycle (Face_const_handle f)
returns a circulator for the outer face cycle of f.

Hole_const_iterator holes_begin (Face_const_handle f)
returns an iterator for all holes in the interior of f. More...

Hole_const_iterator holes_end (Face_const_handle f)
returns the past-the-end iterator of f.

Isolated_vertex_const_iterator isolated_vertices_begin (Face_const_handle f)
returns an iterator for all isolated vertices in the interior of f.

Isolated_vertex_const_iterator isolated_vertices_end (Face_const_handle f)
returns the past the end iterator of f.

## Associated Information

The type Mark is the general attribute of an object.

const Pointpoint (Vertex_const_handle v)
returns the embedding of v.

const Markmark (Vertex_const_handle v)
returns the mark of v.

const Markmark (Halfedge_const_handle e)
returns the mark of e.

const Markmark (Face_const_handle f)
returns the mark of f.

## Statistics and Integrity

Size_type number_of_vertices ()
returns the number of vertices.

Size_type number_of_halfedges ()
returns the number of halfedges.

Size_type number_of_edges ()
returns the number of halfedge pairs.

Size_type number_of_faces ()
returns the number of faces.

Size_type number_of_face_cycles ()
returns the number of face cycles.

Size_type number_of_connected_components ()
calculates the number of connected components of P.

void print_statistics (std::ostream &os=std::cout)
print the statistics of P: the number of vertices, edges, and faces.

void check_integrity_and_topological_planarity (bool faces=true)
checks the link structure and the genus of P.

## ◆ Hole_const_iterator

template<typename T>

iterating all holes of a face f.

The type is convertible to Halfedge_const_handle.

## ◆ Isolated_vertex_const_iterator

template<typename T>

iterating all isolated vertices of a face f.

The type generalizes Vertex_const_handle.

## ◆ face()

template<typename T>
 Face_const_handle CGAL::Nef_polyhedron_2< T >::Topological_explorer::face ( Vertex_const_handle v )

returns the face incident to v.

Precondition
is_isolated(v).

## ◆ first_out_edge()

template<typename T>
 Halfedge_const_handle CGAL::Nef_polyhedron_2< T >::Topological_explorer::first_out_edge ( Vertex_const_handle v )

returns one halfedge with source v.

It's the starting point for the circular iteration over the halfedges with source v.

Precondition
!is_isolated(v).

## ◆ holes_begin()

template<typename T>
 Hole_const_iterator CGAL::Nef_polyhedron_2< T >::Topological_explorer::holes_begin ( Face_const_handle f )

returns an iterator for all holes in the interior of f.

A Hole_iterator can be assigned to a Halfedge_around_face_const_circulator.

## ◆ last_out_edge()

template<typename T>
 Halfedge_const_handle CGAL::Nef_polyhedron_2< T >::Topological_explorer::last_out_edge ( Vertex_const_handle v )

returns the halfedge with source v that is the last in the circular iteration before encountering first_out_edge(v) again.

Precondition
!is_isolated(v).