CGAL 6.1.2 - 3D Convex Hulls

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Functions
Convex Hull Functions
Reference Manual

##

The function `convex_hull_3()` computes the convex hull of a given set of three-dimensional points.

Two versions of this function are available. The first can be used when it is known that the result will be a polyhedron and the second when a degenerate hull may also be possible.

## Functions
template<class InputIterator , class PolygonMesh , class Traits >
void | CGAL::convex_hull_3 (InputIterator first, InputIterator last, PolygonMesh &pm, const Traits &ch_traits=Default_traits)
| computes the convex hull of the set of points in the range [`first`, `last`).
template<class VertexListGraph , class PolygonMesh , class NamedParameters = parameters::Default_named_parameters>
void | CGAL::convex_hull_3 (const VertexListGraph &g, PolygonMesh &pm, const NamedParameters &np=parameters::default_values())
| computes the convex hull of the points associated to the vertices of `g`.
template<class InputIterator , class Traits >
void | CGAL::convex_hull_3 (InputIterator first, InputIterator last, Object &ch_object, const Traits &ch_traits=Default_traits)
| computes the convex hull of the set of points in the range [`first`, `last`).
template<class InputIterator , class PointRange , class PolygonRange class Traits>
void | CGAL::convex_hull_3 (InputIterator first, InputIterator last, PointRange &vertices, PolygonRange &faces, const Traits &ch_traits=Default_traits)
| computes the convex hull of the set of points in the range [`first`, `last`).
template<class InputRange , class OutputIterator , class Traits >
OutputIterator | CGAL::extreme_points_3 (InputRange range, OutputIterator out, const Traits &traits)
| copies in `out` the points on the convex hull of the points in `range`.
template<class PlaneIterator , class PolygonMesh >
void | CGAL::halfspace_intersection_3 (PlaneIterator begin, PlaneIterator end, PolygonMesh &pm, std::optional< Kernel_traits< std::iterator_traits< PlaneIterator >::value_type >::Kernel::Point_3 > > origin=std::nullopt)
| computes robustly the intersection of the halfspaces defined by the planes contained in the range [`begin`, `end`) without constructing the dual points.
template<class PlaneIterator , class PolygonMesh , class Traits >
void | CGAL::halfspace_intersection_with_constructions_3 (PlaneIterator pbegin, PlaneIterator pend, PolygonMesh &pm, std::optional< Kernel_traits< std::iterator_traits< PlaneIterator >::value_type >::Kernel::Point_3 > > origin=std::nullopt, const Traits &ch_traits=Default_traits)
| computes the intersection of the halfspaces defined by the planes contained in the range [`begin`, `end`).
template<class Triangulation , class PolygonMesh >
void | CGAL::convex_hull_3_to_face_graph (const Triangulation &T, PolygonMesh &pm)
| fills a polyhedron with the convex hull of a set of 3D points contained in a 3D triangulation of CGAL.
template<class PointPropertyMap , class Base_traits >
Extreme_points_traits_adapter_3< PointPropertyMap, Base_traits > | CGAL::make_extreme_points_traits_adapter (const PointPropertyMap &pmap, Base_traits traits)
| Returns `Extreme_points_traits_adapter_3<PointPropertyMap, Base_traits>(pmap, traits)`.
template<class PlaneIterator >
std::optional< typename Kernel_traits< typename std::iterator_traits< PlaneIterator >::value_type >::Kernel::Point_3 > | CGAL::halfspace_intersection_interior_point_3 (PlaneIterator begin, PlaneIterator end)
| computes a point belonging to the intersection of the halfspaces defined by the planes contained in the range `[begin, end)`.

## Function Documentation

## ◆ convex_hull_3() [1/4]

template<class VertexListGraph , class PolygonMesh , class NamedParameters = parameters::Default_named_parameters>

void CGAL::convex_hull_3 | ( | const VertexListGraph & | g,
|  | PolygonMesh & | pm,
|  | const NamedParameters & | np = `parameters::default_values()`
| ) |  |

`#include <CGAL/convex_hull_3.h>`

computes the convex hull of the points associated to the vertices of `g`.

The polygon mesh `pm` is cleared, then the convex hull is stored in `pm`. Note that the convex hull will be triangulated, that is `pm` will contain only triangular faces. if the convex hull is a point or a segment, endpoints will be added in `pm` as isolated vertices.

Template Parameters

  VertexListGraph | a model of `VertexListGraph`.
  PolygonMesh | must be a model of `MutableFaceGraph`. an internal property map for `CGAL::vertex_point_t` must be available.
  NamedParameters | a sequence of named parameters

Parameters

  g | the graph
  pm | the `PolygonMesh` that will contain the convex hull
  np | an optional sequence of Named Parameters among the ones listed below

Optional Named Parameters

  a property map associating points to the vertices of `g` Type: a class model of `ReadablePropertyMap` with `boost::graph_traits<VertexListGraph>::vertex_descriptor` as key type and `Point_3` as value type Default: `boost::get(CGAL::vertex_point, g)` Extra: If this parameter is omitted, an internal property map for `CGAL::vertex_point_t` must be available in `VertexListGraph`. |

Attention
  The user must include the header file of the `PolygonMesh` and `VertexListGraph` types.

## ◆ convex_hull_3() [2/4]

template<class InputIterator , class Traits >

void CGAL::convex_hull_3 | ( | InputIterator | first,
|  | InputIterator | last,
|  | Object & | ch_object,
|  | const Traits & | ch_traits = `Default_traits`
| ) |  |

`#include <CGAL/convex_hull_3.h>`

computes the convex hull of the set of points in the range [`first`, `last`).

The result, which may be a point, a segment, a triangle, or a polygon mesh, is stored in `ch_object`. In the case the result is a polygon mesh, the convex hull will be triangulated, that is the polygon mesh will contain only triangular facets.

Template Parameters

  InputIterator | must be an input iterator with a value type equivalent to `Traits::Point_3`.
  Traits | must be model of the concept `ConvexHullTraits_3`. For the purposes of checking the postcondition that the convex hull is valid, `Traits` must also be a model of the concept `IsStronglyConvexTraits_3`. Furthermore, `Traits` must define a type `PolygonMesh` that is a model of `MutableFaceGraph`.

If the kernel `R` of the points determined by the value type of `InputIterator` is a kernel with exact predicates but inexact constructions (in practice we check `R::Has_filtered_predicates_tag` is `Tag_true` and `R::FT` is a floating point type), then the default traits class of `convex_hull_3()` is `Convex_hull_traits_3<R>`, and `R` otherwise.

Attention
  The user must include the header file of the `PolygonMesh` type.

## ◆ convex_hull_3() [3/4]

template<class InputIterator , class PointRange , class PolygonRange class Traits>

void CGAL::convex_hull_3 | ( | InputIterator | first,
|  | InputIterator | last,
|  | PointRange & | vertices,
|  | PolygonRange & | faces,
|  | const Traits & | ch_traits = `Default_traits`
| ) |  |

`#include <CGAL/convex_hull_3.h>`

computes the convex hull of the set of points in the range [`first`, `last`).

The result, which may be a point, a segment, a triangle, or a triangle mesh, is stored as an indexed triangle soup in a vector of points and a vector of index triples.

Template Parameters

  InputIterator | must be an input iterator with a value type equivalent to `Traits::Point_3`.
  PointRange | a model of the concept `RandomAccessContainer` whose value type is the point type.
  PolygonRange | a model of the concepts `RandomAccessContainer` and `BackInsertionSequence` whose `value_type` is itself a model of the concepts `RandomAccessContainer` and `BackInsertionSequence` whose `value_type` is an unsigned integer type convertible to `std::size_t`
  Traits | must be model of the concept `ConvexHullTraits_3`. For the purposes of checking the postcondition that the convex hull is valid, `Traits` must also be a model of the concept `IsStronglyConvexTraits_3`.

If the kernel `R` of the points determined by the value type of `InputIterator` is a kernel with exact predicates but inexact constructions (in practice we check `R::Has_filtered_predicates_tag` is `Tag_true` and `R::FT` is a floating point type), then the default traits class of `convex_hull_3()` is `Convex_hull_traits_3<R>`, and `R` otherwise.

## ◆ convex_hull_3() [4/4]

template<class InputIterator , class PolygonMesh , class Traits >

void CGAL::convex_hull_3 | ( | InputIterator | first,
|  | InputIterator | last,
|  | PolygonMesh & | pm,
|  | const Traits & | ch_traits = `Default_traits`
| ) |  |

`#include <CGAL/convex_hull_3.h>`

computes the convex hull of the set of points in the range [`first`, `last`).

The polygon mesh `pm` is cleared, then the convex hull is stored in `pm`. Note that the convex hull will be triangulated, that is `pm` will contain only triangular facets. if the convex hull is a point or a segment, endpoints will be added in `pm` as isolated vertices.

Template Parameters

  InputIterator | must be an input iterator with a value type equivalent to `Traits::Point_3`.
  PolygonMesh | must be a model of `MutableFaceGraph`.
  Traits | must be a model of the concept `ConvexHullTraits_3`. For the purposes of checking the postcondition that the convex hull is valid, `Traits` must also be a model of the concept `IsStronglyConvexTraits_3`.

If the kernel `R` of the points determined by the value type of `InputIterator` is a kernel with exact predicates but inexact constructions (in practice we check `R::Has_filtered_predicates_tag` is `Tag_true` and `R::FT` is a floating point type), then the default traits class of `convex_hull_3()` is `Convex_hull_traits_3<R>`, and `R` otherwise.

Attention
  The user must include the header file of the `PolygonMesh` type.

Implementation

The algorithm implemented by these functions is the quickhull algorithm of Barber et al. [1].

Examples
  Convex_hull_3/quickhull_3.cpp, Convex_hull_3/quickhull_OM_3.cpp, Convex_hull_3/quickhull_any_dim_3.cpp, and Convex_hull_3/quickhull_indexed_triangle_set_3.cpp.

## ◆ convex_hull_3_to_face_graph()

template<class Triangulation , class PolygonMesh >

void CGAL::convex_hull_3_to_face_graph | ( | const Triangulation & | T,
|  | PolygonMesh & | pm
| ) |  |

`#include <CGAL/convex_hull_3_to_face_graph.h>`

fills a polyhedron with the convex hull of a set of 3D points contained in a 3D triangulation of CGAL.

The polyhedron `pm` is cleared and the convex hull of the set of 3D points is stored in `pm`.

Precondition
  `T.dimension()`==3.

Template Parameters

  Triangulation | must be a CGAL 3D triangulation
  PolygonMesh | must be a model of the concept `MutableFaceGraph`

See also
  `convex_hull_3()`
  `link_to_face_graph()`

Examples
  Convex_hull_3/dynamic_hull_3.cpp, and Convex_hull_3/dynamic_hull_OM_3.cpp.

## ◆ extreme_points_3()

template<class InputRange , class OutputIterator , class Traits >

OutputIterator CGAL::extreme_points_3 | ( | InputRange | range,
|  | OutputIterator | out,
|  | const Traits & | traits
| ) |  |

`#include <CGAL/convex_hull_3.h>`

copies in `out` the points on the convex hull of the points in `range`.

Template Parameters

  InputRange | a range of `Traits::Point_3`, model of `ConstRange`. Its iterator type is `InputIterator`.
  OutputIterator | must be an output iterator where points of type `Traits::Point_3` can be put.
  Traits | must be model of the concept `ConvexHullTraits_3`.

If the kernel `R` of the points from `InputRange` is a kernel with exact predicates but inexact constructions (in practice we check `R::Has_filtered_predicates_tag` is `Tag_true` and `R::FT` is a floating point type), then the default traits class used is `Convex_hull_traits_3<R>`, and `R` otherwise.

Parameters

  range | the range of input points.
  out | an output iterator where the extreme points will be put.
  traits | an instance of `Traits`.

See also
  `CGAL::Extreme_points_traits_adapter_3`

Examples
  Convex_hull_3/extreme_indices_3.cpp, and Convex_hull_3/extreme_points_3_sm.cpp.

## ◆ halfspace_intersection_3()

template<class PlaneIterator , class PolygonMesh >

void CGAL::halfspace_intersection_3 | ( | PlaneIterator | begin,
|  | PlaneIterator | end,
|  | PolygonMesh & | pm,
|  | std::optional< Kernel_traits< std::iterator_traits< PlaneIterator >::value_type >::Kernel::Point_3 > | ,
|  | origin | = `std::nullopt`
| ) |  |

`#include <CGAL/Convex_hull_3/dual/halfspace_intersection_3.h>`

computes robustly the intersection of the halfspaces defined by the planes contained in the range [`begin`, `end`) without constructing the dual points.

The result is stored in the polyhedron `pm`. If `origin` is given then it must be a point strictly inside the polyhedron. If an interior point is not given then it is computed using the function `halfspace_intersection_interior_point_3()` based on solving a linear program and thus is slower.

This version does not construct the dual points explicitly but uses a special traits class for the function `CGAL::convex_hull_3()` to handle predicates on dual points without constructing them.

Halfspaces are considered as lower halfspaces, that is if the plane equation is \( a\, x +b\, y +c\, z + d = 0 \) then the corresponding halfspace is defined by \( a\, x +b\, y +c\, z + d \le 0 \) .

Precondition
  The point type of `origin` and the point type of the vertices of `PolygonMesh` must come from the same CGAL Kernel.
  if provided, `origin` is inside the intersection of halfspaces defined by the range `[begin, end)`.
  The computed intersection must be a bounded convex polyhedron.

Template Parameters

  PlaneIterator | must be an input iterator where the value type is a model of the concept `Kernel::Plane_3` and this plane type must come from the same kernel as the point type.
  PolygonMesh | must be a model of `MutableFaceGraph`.

See also
  `halfspace_intersection_with_constructions_3()`

Examples
  Convex_hull_3/halfspace_intersection_3.cpp.

## ◆ halfspace_intersection_interior_point_3()

template<class PlaneIterator >

std::optional< typename Kernel_traits< typename std::iterator_traits< PlaneIterator >::value_type >::Kernel::Point_3 > CGAL::halfspace_intersection_interior_point_3 | ( | PlaneIterator | begin,
|  | PlaneIterator | end
| ) |  |

`#include <CGAL/Convex_hull_3/dual/halfspace_intersection_interior_point_3.h>`

computes a point belonging to the intersection of the halfspaces defined by the planes contained in the range `[begin, end)`.

If the intersection is empty, `std::nullopt` is returned.

Attention
  Halfspaces are considered as lower halfspaces that is to say if the plane's equation is \( a\, x +b\, y +c\, z + d = 0 \) then the corresponding halfspace is defined by \( a\, x +b\, y +c\, z + d \le 0 \) .

Template Parameters

  PlaneIterator | must be an input iterator with the value type being a `Plane_3` object from CGAL Kernel

## ◆ halfspace_intersection_with_constructions_3()

template<class PlaneIterator , class PolygonMesh , class Traits >

void CGAL::halfspace_intersection_with_constructions_3 | ( | PlaneIterator | pbegin,
|  | PlaneIterator | pend,
|  | PolygonMesh & | pm,
|  | std::optional< Kernel_traits< std::iterator_traits< PlaneIterator >::value_type >::Kernel::Point_3 > | ,
|  | origin | = `std::nullopt`,
|  | const Traits & | ch_traits = `Default_traits`
| ) |  |

`#include <CGAL/Convex_hull_3/dual/halfspace_intersection_with_constructions_3.h>`

computes the intersection of the halfspaces defined by the planes contained in the range [`begin`, `end`).

The result is stored in the polyhedron `pm`. If `origin` is given then it must be a point strictly inside the polyhedron. If an interior point is not given then it is computed using the function `halfspace_intersection_interior_point_3()` based on solving a linear program and thus is slower. This version constructs explicitly the dual points using the convex hull algorithm parametrized with the given traits class.

Halfspaces are considered as lower halfspaces, that is if the plane equation is \( a\, x +b\, y +c\, z + d = 0 \) then the corresponding halfspace is defined by \( a\, x +b\, y +c\, z + d \le 0 \) .

Precondition
  The value type of `PlaneIterator` and the point type of `origin` must come from the same CGAL Kernel.
  if provided, `origin` is inside the intersection of halfspaces defined by the range `[begin, end)`.
  The computed intersection must be a bounded convex polyhedron.

Template Parameters

  PlaneIterator | must be an input iterator where the value type is a model of the concept `Kernel::Plane_3` and this plane type must come from the same kernel as the point type.
  PolygonMesh | must be a model of `MutableFaceGraph`.
  Traits | must be a model of the concept `ConvexHullTraits_3`.

See also
  `halfspace_intersection_3()`