CGAL 6.2 - Bounding Volumes

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CGAL::Min_annulus_d< Traits > Class Template Reference
Reference Manual

`#include <CGAL/Min_annulus_d.h>`

## Definition

template<typename Traits>
class CGAL::Min_annulus_d< Traits >

An object of the class `Min_annulus_d` is the unique annulus (region between two concentric spheres with radii \( r\) and \( R\), \( r \leq R\)) enclosing a finite set of points in \( d\)-dimensional Euclidean space \( \E^d\), where the difference \( R^2-r^2\) is minimal.

For a point set \( P\) we denote by \( ma(P)\) the smallest annulus that contains all points of \( P\). Note that \( ma(P)\) can be degenerate, i.e. \( ma(P)=\emptyset\) if \( P=\emptyset\) and \( ma(P)=\{p\}\) if \( P=\{p\}\).

An inclusion-minimal subset \( S\) of \( P\) with \( ma(S)=ma(P)\) is called a support set, the points in \( S\) are the support points. A support set has size at most \( d+2\), and all its points lie on the boundary of \( ma(P)\). In general, the support set is not necessarily unique.

The underlying algorithm can cope with all kinds of input, e.g. \( P\) may be empty or points may occur more than once. The algorithm computes a support set \( S\) which remains fixed until the next set, insert, or clear operation.

Template Parameters

  Traits | must be a model for `MinSphereAnnulusDTraits`.

We provide the models `Min_sphere_annulus_d_traits_2`, `Min_sphere_annulus_d_traits_3`, and `Min_sphere_annulus_d_traits_d` using the two-, three-, and \( d\)-dimensional CGAL kernel, respectively.

See also
  `CGAL::Min_sphere_d<Traits>`
  `CGAL::Min_sphere_annulus_d_traits_2<K,ET,NT>`
  `CGAL::Min_sphere_annulus_d_traits_3<K,ET,NT>`
  `CGAL::Min_sphere_annulus_d_traits_d<K,ET,NT>`
  `MinSphereAnnulusDTraits`

Implementation

The problem of finding the smallest enclosing annulus of a finite point set can be formulated as an optimization problem with linear constraints and a linear objective function. The solution is obtained using our exact solver for linear and quadratic programs [7].

The creation time is almost always linear in the number of points. Access functions and predicates take constant time, inserting a point takes almost always linear time. The clear operation and the check for validity each take linear time.

Examples
  Min_annulus_d/min_annulus_d.cpp, and Min_annulus_d/min_annulus_d_fast_exact.cpp.

## Related Functions
(Note that these are not member functions.)
std::ostream & | operator<< (std::ostream &os, const Min_annulus_d< Traits > &min_annulus)
| writes `min_annulus` to output stream `os`.
std::istream & | operator>> (std::istream &is, Min_annulus_d< Traits > min_annulus &)
| reads `min_annulus` from input stream `is`.

## Types
typedef unspecified_type | Point
| typedef to `Traits::Point_d`.
typedef unspecified_type | FT
| typedef to `Traits::FT`.
typedef unspecified_type | ET
| typedef to `Traits::ET`.
typedef unspecified_type | Point_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `Point`.
typedef unspecified_type | Support_point_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `Point`.
typedef unspecified_type | Inner_support_point_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `Point`.
typedef unspecified_type | Outer_support_point_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `Point`.
typedef unspecified_type | Coordinate_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `ET`.

## Creation
| Min_annulus_d (const Traits &traits=Traits(), int verbose=0, std::ostream &stream=std::cout)
| initializes `min_annulus` to \( ma(\emptyset)\).
template<class InputIterator >
| Min_annulus_d (InputIterator first, InputIterator last, const Traits &traits=Traits(), int verbose=0, std::ostream &stream=std::cout)
| initializes `min_annulus` to \( ma(P)\) with \( P\) being the set of points in the range [`first`,`last`).

## Access Functions
int | ambient_dimension () const
| returns the dimension of the points in \( P\).
int | number_of_points () const
| returns the number of points of `min_annulus`, i.e. \( |P|\).
int | number_of_support_points () const
| returns the number of support points of `min_annulus`, i.e. \( |S|\).
int | number_of_inner_support_points () const
| returns the number of support points of `min_annulus` which lie on the inner sphere.
int | number_of_outer_support_points () const
| returns the number of support points of `min_annulus` which lie on the outer sphere.
Point_iterator | points_begin () const
| returns an iterator referring to the first point of `min_annulus`.
Point_iterator | points_end () const
| returns the corresponding past-the-end iterator.
Support_point_iterator | support_points_begin () const
| returns an iterator referring to the first support point of `min_annulus`.
Support_point_iterator | support_points_end () const
| returns the corresponding past-the-end iterator.
Inner_support_point_iterator | inner_support_points_begin () const
| returns an iterator referring to the first inner support point of `min_annulus`.
Inner_support_point_iterator | inner_support_points_end () const
| returns the corresponding past-the-end iterator.
Outer_support_point_iterator | outer_support_points_begin () const
| returns an iterator referring to the first outer support point of `min_annulus`.
Outer_support_point_iterator | outer_support_points_end () const
| returns the corresponding past-the-end iterator.
Point | center () const
| returns the center of `min_annulus`.
FT | squared_inner_radius () const
| returns the squared inner radius of `min_annulus`.
FT | squared_outer_radius () const
| returns the squared outer radius of `min_annulus`.
Coordinate_iterator | center_coordinates_begin () const
| returns an iterator referring to the first coordinate of the center of `min_annulus`.
Coordinate_iterator | center_coordinates_end () const
| returns the corresponding past-the-end iterator.
ET | squared_inner_radius_numerator () const
| returns the numerator of the squared inner radius of `min_annulus`.
ET | squared_outer_radius_numerator () const
| returns the numerator of the squared outer radius of `min_annulus`.
ET | squared_radii_denominator () const
| returns the denominator of the squared radii of `min_annulus`.

## Predicates
The bounded area of the smallest enclosing annulus lies between the inner and the outer sphere. The boundary is the union of both spheres. By definition, an empty annulus has no boundary and no bounded side, i.e. its unbounded side equals the whole space \( \E^d\).
CGAL::Bounded_side | bounded_side (const Point &p) const
| returns `CGAL::ON_BOUNDED_SIDE`, `CGAL::ON_BOUNDARY`, or `CGAL::ON_UNBOUNDED_SIDE` iff `p` lies properly inside, on the boundary, or properly outside of `min_annulus`, resp.
bool | has_on_bounded_side (const Point &p) const
| returns `true`, iff `p` lies properly inside `min_annulus`.
bool | has_on_boundary (const Point &p) const
| returns `true`, iff `p` lies on the boundary of `min_annulus`.
bool | has_on_unbounded_side (const Point &p) const
| returns `true`, iff `p` lies properly outside of `min_annulus`.
bool | is_empty () const
| returns `true`, iff `min_annulus` is empty (this implies degeneracy).
bool | is_degenerate () const
| returns `true`, iff `min_annulus` is degenerate, i.e. if `min_annulus` is empty or equal to a single point.

## Modifiers
void | clear ()
| resets `min_annulus` to \( ma(\emptyset)\).
template<class InputIterator >
void | set (InputIterator first, InputIterator last)
| sets `min_annulus` to \( ma(P)\), where \( P\) is the set of points in the range [`first`,`last`).
void | insert (const Point &p)
| inserts `p` into `min_annulus`.
template<class InputIterator >
void | insert (InputIterator first, InputIterator last)
| inserts the points in the range [`first`,`last`) into `min_annulus` and recomputes the smallest enclosing annulus.

## Validity Check
An object `min_annulus` is valid, iff `min_annulus` contains all points of its defining set \( P\), `min_annulus` is the smallest annulus containing its support set \( S\), and \( S\) is minimal, i.e. no support point is redundant. Note: In this release only the first item is considered by the validity check.
bool | is_valid (bool verbose=false, int level=0) const
| returns `true`, iff `min_annulus` is valid.

## Miscellaneous
const Traits & | traits () const
| returns a const reference to the traits class object.

## Member Typedef Documentation

## ◆ Coordinate_iterator

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::Coordinate_iterator

non-mutable model of the STL concept RandomAccessIterator with value type `ET`.

Used to access the coordinates of the center of the smallest enclosing annulus.

## ◆ ET

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::ET

typedef to `Traits::ET`.

Number type used to do the exact computations in the underlying solver for quadratic programs (cf. Implementation).

## ◆ FT

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::FT

typedef to `Traits::FT`.

Number type used to return the squared radii of the smallest enclosing annulus.

## ◆ Inner_support_point_iterator

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::Inner_support_point_iterator

non-mutable model of the STL concept RandomAccessIterator with value type `Point`.

Used to access the inner support points of the smallest enclosing annulus.

## ◆ Outer_support_point_iterator

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::Outer_support_point_iterator

non-mutable model of the STL concept RandomAccessIterator with value type `Point`.

Used to access the outer support points of the smallest enclosing annulus.

## ◆ Point

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::Point

typedef to `Traits::Point_d`.

Point type used to represent the input points.

## ◆ Point_iterator

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::Point_iterator

non-mutable model of the STL concept RandomAccessIterator with value type `Point`.

Used to access the points of the smallest enclosing annulus.

## ◆ Support_point_iterator

template<typename Traits >

typedef unspecified_type CGAL::Min_annulus_d< Traits >::Support_point_iterator

non-mutable model of the STL concept RandomAccessIterator with value type `Point`.

Used to access the support points of the smallest enclosing annulus.

## Constructor & Destructor Documentation

## ◆ Min_annulus_d()

template<typename Traits >
template<class InputIterator >

CGAL::Min_annulus_d< Traits >::Min_annulus_d | ( | InputIterator | first,
|  | InputIterator | last,
|  | const Traits & | traits = `Traits()`,
|  | int | verbose = `0`,
|  | std::ostream & | stream = `std::cout`
| ) |  |

initializes `min_annulus` to \( ma(P)\) with \( P\) being the set of points in the range [`first`,`last`).

Template Parameters

  InputIterator | is a model of `InputIterator` with `Point` as value type.

Precondition
  All points have the same dimension.

## Member Function Documentation

## ◆ ambient_dimension()

template<typename Traits >

int CGAL::Min_annulus_d< Traits >::ambient_dimension | ( |  | ) | const

returns the dimension of the points in \( P\).

If `min_annulus` is empty, the ambient dimension is \( -1\).

## ◆ bounded_side()

template<typename Traits >

CGAL::Bounded_side CGAL::Min_annulus_d< Traits >::bounded_side | ( | const Point & | p | ) | const

returns `CGAL::ON_BOUNDED_SIDE`, `CGAL::ON_BOUNDARY`, or `CGAL::ON_UNBOUNDED_SIDE` iff `p` lies properly inside, on the boundary, or properly outside of `min_annulus`, resp.

Precondition
  The dimension of `p` equals `min_annulus.ambient_dimension()` if `min_annulus` is not empty.

## ◆ center()

template<typename Traits >

Point CGAL::Min_annulus_d< Traits >::center | ( |  | ) | const

returns the center of `min_annulus`.

An implicit conversion from `ET` to `RT` must be available.

Precondition
  `min_annulus` is not empty.

## ◆ center_coordinates_begin()

template<typename Traits >

Coordinate_iterator CGAL::Min_annulus_d< Traits >::center_coordinates_begin | ( |  | ) | const

returns an iterator referring to the first coordinate of the center of `min_annulus`.

Note
  The coordinates have a rational representation, i.e. the first \( d\) elements of the iterator range are the numerators and the \( (d\!+\!1)\)-st element is the common denominator.

## ◆ has_on_boundary()

template<typename Traits >

bool CGAL::Min_annulus_d< Traits >::has_on_boundary | ( | const Point & | p | ) | const

returns `true`, iff `p` lies on the boundary of `min_annulus`.

Precondition
  The dimension of `p` equals `min_annulus.ambient_dimension()` if `min_annulus` is not empty.

## ◆ has_on_bounded_side()

template<typename Traits >

bool CGAL::Min_annulus_d< Traits >::has_on_bounded_side | ( | const Point & | p | ) | const

returns `true`, iff `p` lies properly inside `min_annulus`.

Precondition
  The dimension of `p` equals `min_annulus.ambient_dimension()` if `min_annulus` is not empty.

## ◆ has_on_unbounded_side()

template<typename Traits >

bool CGAL::Min_annulus_d< Traits >::has_on_unbounded_side | ( | const Point & | p | ) | const

returns `true`, iff `p` lies properly outside of `min_annulus`.

Precondition
  The dimension of `p` equals `min_annulus.ambient_dimension()` if `min_annulus` is not empty.

## ◆ insert() [1/2]

template<typename Traits >

void CGAL::Min_annulus_d< Traits >::insert | ( | const Point & | p | ) |

inserts `p` into `min_annulus`.

Precondition
  The dimension of `p` equals `min_annulus.ambient_dimension()` if `min_annulus` is not empty.

## ◆ insert() [2/2]

template<typename Traits >
template<class InputIterator >

void CGAL::Min_annulus_d< Traits >::insert | ( | InputIterator | first,
|  | InputIterator | last
| ) |  |

inserts the points in the range [`first`,`last`) into `min_annulus` and recomputes the smallest enclosing annulus.

Template Parameters

  InputIterator | is a model of `InputIterator` with `Point` as value type.

Precondition
  All points have the same dimension. If `min_annulus` is not empty, this dimension must be equal to `min_annulus.ambient_dimension()`.

## ◆ is_valid()

template<typename Traits >

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

returns `true`, iff `min_annulus` is valid.

If `verbose` is `true`, some messages concerning the performed checks are written to standard error stream. The second parameter `level` is not used, we provide it only for consistency with interfaces of other classes.

## ◆ set()

template<typename Traits >
template<class InputIterator >

void CGAL::Min_annulus_d< Traits >::set | ( | InputIterator | first,
|  | InputIterator | last
| ) |  |

sets `min_annulus` to \( ma(P)\), where \( P\) is the set of points in the range [`first`,`last`).

Template Parameters

  InputIterator | is a model of `InputIterator` with `Point` as value type.

Precondition
  All points have the same dimension.

## ◆ squared_inner_radius()

template<typename Traits >

FT CGAL::Min_annulus_d< Traits >::squared_inner_radius | ( |  | ) | const

returns the squared inner radius of `min_annulus`.

An implicit conversion from `ET` to `RT` must be available.

Precondition
  `min_annulus` is not empty.

## ◆ squared_outer_radius()

template<typename Traits >

FT CGAL::Min_annulus_d< Traits >::squared_outer_radius | ( |  | ) | const

returns the squared outer radius of `min_annulus`.

An implicit conversion from `ET` to `RT` must be available.

Precondition
  `min_annulus` is not empty.

## ◆ support_points_begin()

template<typename Traits >

Support_point_iterator CGAL::Min_annulus_d< Traits >::support_points_begin | ( |  | ) | const

returns an iterator referring to the first support point of `min_annulus`.

Precondition
  \( ma(P)\) is not degenerate, i.e., `number_of_support_points()` is at least one.

## ◆ support_points_end()

template<typename Traits >

Support_point_iterator CGAL::Min_annulus_d< Traits >::support_points_end | ( |  | ) | const

returns the corresponding past-the-end iterator.

Precondition
  \( ma(P)\) is not degenerate, i.e., `number_of_support_points()` is at least one.

## Friends And Related Function Documentation

## ◆ operator<<()

template<typename Traits >

std::ostream & operator<< | ( | std::ostream & | os,
|  | const Min_annulus_d< Traits > & | min_annulus
| ) |  |
| related

writes `min_annulus` to output stream `os`.

An overload of `operator<<` must be defined for `Point`.

## ◆ operator>>()

template<typename Traits >

std::istream & operator>> | ( | std::istream & | is,
|  | Min_annulus_d< Traits > min_annulus & |
| ) |  |
| related

reads `min_annulus` from input stream `is`.

An overload of `operator>>` must be defined for `Point`.