CGAL 6.1 - Optimal Distances

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

`#include <CGAL/Polytope_distance_d.h>`

## Definition

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

An object of the class `Polytope_distance_d` represents the (squared) distance between two convex polytopes, given as the convex hulls of two finite point sets in \( d\)-dimensional Euclidean space \( \E^d\).

For point sets \( P\) and \( Q\) we denote by \( pd(P,Q)\) the distance between the convex hulls of \( P\) and \( Q\). Note that \( pd(P,Q)\) can be degenerate, i.e. \( pd(P,Q)=\infty\) if \( P\) or \( Q\) is empty.

Two inclusion-minimal subsets \( S_P\) of \( P\) and \( S_Q\) of \( Q\) with \( pd(S_P,S_Q)=pd(P,Q)\) are called pair of support sets, the points in \( S_P\) and \( S_Q\) are the support points. A pair of support sets has size at most \( d+2\) (by size we mean \( |S_P|+|S_Q|\)). The distance between the two polytopes is realized by a pair of points \( p\) and \( q\) lying in the convex hull of \( S_P\) and \( S_Q\), respectively, i.e. \( \sqrt{||p-q||}=pd(P,Q)\). In general, neither the support sets nor the realizing points are necessarily unique.

The underlying algorithm can cope with all kinds of input, e.g. \( P\) and \( Q\) may be in non-convex position or points may occur more than once. The algorithm computes a pair of support sets \( S_P\) and \( S_Q\) with realizing points \( p\) and \( q\) which remain fixed until the next set, insert, or clear operation.

Template Parameters

  Traits | must be a model for `PolytopeDistanceDTraits`.

We provide the models `Polytope_distance_d_traits_2`, `Polytope_distance_d_traits_3`, and `Polytope_distance_d_traits_d` using the two-, three-, and \( d\)-dimensional CGAL kernel, respectively.

See also
  `CGAL::Polytope_distance_d_traits_2<K,ET,NT>`
  `CGAL::Polytope_distance_d_traits_3<K,ET,NT>`
  `CGAL::Polytope_distance_d_traits_d<K,ET,NT>`
  `PolytopeDistanceDTraits`

Implementation

The problem of finding the distance between two convex polytopes given as the convex hulls of two finite point sets can be formulated as an optimization problem with linear constraints and a convex quadratic objective function. The solution is obtained using our exact solver for quadratic programs [2].

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

Examples
  Polytope_distance_d/polytope_distance_d.cpp, and Polytope_distance_d/polytope_distance_d_fast_exact.cpp.

## Related Functions
(Note that these are not member functions.)
std::ostream & | operator<< (std::ostream &os, const Polytope_distance_d< Traits > &poly_dist)
| writes `poly_dist` to output stream `os`.
std::istream & | operator>> (std::istream &is, Polytope_distance_d< Traits > poly_dist &)
| reads `poly_dist` 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 | Support_point_index_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `int`.
typedef unspecified_type | Coordinate_iterator
| non-mutable model of the STL concept RandomAccessIterator with value type `ET`.

## Creation
| Polytope_distance_d (const Traits &traits=Traits(), int verbose=0, std::ostream &stream=std::cout)
| initializes `poly_dist` to \( pd(\emptyset, \emptyset)\).
template<class InputIterator1 , class InputIterator2 >
| Polytope_distance_d (InputIterator1 p_first, InputIterator1 p_last, InputIterator2 q_first, InputIterator2 q_last, const Traits &traits=Traits(), int verbose=0, std::ostream &stream=std::cout)
| initializes `poly_dist` to \( pd(P,Q)\) with \( P\) and \( Q\) being the sets of points in the range [`p_first`,`p_last`) and [`q_first`,`q_last`), respectively.

## Access Functions
int | ambient_dimension () const
| returns the dimension of the points in \( P\) and \( Q\).
int | number_of_points () const
| returns the number of all points of `poly_dist`, i.e. \( |P|+|Q|\).
int | number_of_points_p () const
| returns the number of points in \( P\).
int | number_of_points_q () const
| returns the number of points in \( Q\).
int | number_of_support_points () const
| returns the number of support points of `poly_dist`, i.e. \( |S_P|+|S_Q|\).
int | number_of_support_points_p () const
| returns the number of support points in \( S_P\).
int | number_of_support_points_q () const
| returns the number of support points in \( S_Q\).
Point_iterator | points_p_begin () const
| returns an iterator referring to the first point in \( P\).
Point_iterator | points_p_end () const
| returns the corresponding past-the-end iterator.
Point_iterator | points_q_begin () const
| returns an iterator referring to the first point in \( Q\).
Point_iterator | points_q_end () const
| returns the corresponding past-the-end iterator.
Support_point_iterator | support_points_p_begin () const
| returns an iterator referring to the first support point in \( S_P\).
Support_point_iterator | support_points_p_end () const
| returns the corresponding past-the-end iterator.
Support_point_iterator | support_points_q_begin () const
| returns an iterator referring to the first support point in \( S_Q\).
Support_point_iterator | support_points_q_end () const
| returns the corresponding past-the-end iterator.
Support_point_index_iterator | support_points_p_indices_begin () const
| returns an iterator referring to the index of the first support point in \( P\).
Support_point_index_iterator | support_points_p_indices_end () const
| returns the corresponding past-the-end iterator.
Support_point_index_iterator | support_points_q_indices_begin () const
| returns an iterator referring to the index of the first support point in \( Q\).
Support_point_index_iterator | support_points_q_indices_end () const
| returns the corresponding past-the-end iterator.
Point | realizing_point_p () const
| returns the realizing point of \( P\).
Point | realizing_point_q () const
| returns the realizing point of \( Q\).
FT | squared_distance () const
| returns the squared distance of `poly_dist`, i.e. \( (pd(P,Q))^2\).
Coordinate_iterator | realizing_point_p_coordinates_begin () const
| returns an iterator referring to the first coordinate of the realizing point of \( P\).
Coordinate_iterator | realizing_point_p_coordinates_end () const
| returns the corresponding past-the-end iterator.
Coordinate_iterator | realizing_point_q_coordinates_begin () const
| returns an iterator referring to the first coordinate of the realizing point of \( Q\).
Coordinate_iterator | realizing_point_q_coordinates_end () const
| returns the corresponding past-the-end iterator.
ET | squared_distance_numerator () const
| returns the numerator of the squared distance of `poly_dist`.
ET | squared_distance_denominator () const
| returns the denominator of the squared distance of `poly_dist`.

## Predicates
bool | is_finite () const
| returns `true`, if \( pd(P,Q)\) is finite, i.e. none of the two polytopes is empty.
bool | is_zero () const
| returns `true`, if \( pd(P,Q)\) is zero, i.e. the two polytopes intersect (this implies degeneracy).
bool | is_degenerate () const
| returns `true`, iff \( pd(P,Q)\) is degenerate, i.e. \( pd(P,Q)\) is not finite.

## Modifiers
void | clear ()
| resets `poly_dist` to \( pd(\emptyset, \emptyset)\).
template<class InputIterator1 , class InputIterator2 >
void | set (InputIterator1 p_first, InputIterator1 p_last, InputIterator2 q_first, InputIterator2 q_last)
| sets `poly_dist` to \( pd(P,Q)\) with \( P\) and \( Q\) being the sets of points in the ranges [`p_first`,`p_last`) and [`q_first`,`q_last`), respectively.
template<class InputIterator >
void | set_p (InputIterator p_first, InputIterator p_last)
| sets `poly_dist` to \( pd(P,Q)\) with \( P\) being the set of points in the range [`p_first`,`p_last`) ( \( Q\) remains unchanged).
template<class InputIterator >
void | set_q (InputIterator q_first, InputIterator q_last)
| sets `poly_dist` to \( pd(P,Q)\) with \( Q\) being the set of points in the range [`q_first`,`q_last`) ( \( P\) remains unchanged).
void | insert_p (const Point &p)
| inserts `p` into \( P\).
void | insert_q (const Point &q)
| inserts `q` into \( Q\).
template<class InputIterator1 , class InputIterator2 >
void | insert (InputIterator1 p_first, InputIterator1 p_last, InputIterator2 q_first, InputIterator2 q_last)
| inserts the points in the range [`p_first`,`p_last`) and [`q_first`,`q_last`) into \( P\) and \( Q\), respectively, and recomputes the (squared) distance.
template<class InputIterator >
void | insert_p (InputIterator p_first, InputIterator p_last)
| inserts the points in the range [`p_first`,`p_last`) into \( P\) and recomputes the (squared) distance ( \( Q\) remains unchanged).
template<class InputIterator >
void | insert_q (InputIterator q_first, InputIterator q_last)
| inserts the points in the range [`q_first`,`q_last`) into \( Q\) and recomputes the (squared) distance ( \( P\) remains unchanged).

## Validity Check
bool | is_valid (bool verbose=false, int level=0) const
| returns `true`, iff `poly_dist` 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::Polytope_distance_d< Traits >::Coordinate_iterator

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

Used to access the coordinates of the realizing points.

## ◆ ET

template<typename Traits >

typedef unspecified_type CGAL::Polytope_distance_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::Polytope_distance_d< Traits >::FT

typedef to `Traits::FT`.

Number type used to return the squared distance between the two polytopes.

## ◆ Point

template<typename Traits >

typedef unspecified_type CGAL::Polytope_distance_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::Polytope_distance_d< Traits >::Point_iterator

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

Used to access the points of the two polytopes.

## ◆ Support_point_index_iterator

template<typename Traits >

typedef unspecified_type CGAL::Polytope_distance_d< Traits >::Support_point_index_iterator

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

Used to access the indices of the support points in the provided input order (starting from 0 in both point sets).

## ◆ Support_point_iterator

template<typename Traits >

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

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

Used to access the support points.

## Constructor & Destructor Documentation

## ◆ Polytope_distance_d()

template<typename Traits >
template<class InputIterator1 , class InputIterator2 >

CGAL::Polytope_distance_d< Traits >::Polytope_distance_d | ( | InputIterator1 | p_first,
|  | InputIterator1 | p_last,
|  | InputIterator2 | q_first,
|  | InputIterator2 | q_last,
|  | const Traits & | traits = `Traits()`,
|  | int | verbose = `0`,
|  | std::ostream & | stream = `std::cout`
| ) |  |

initializes `poly_dist` to \( pd(P,Q)\) with \( P\) and \( Q\) being the sets of points in the range [`p_first`,`p_last`) and [`q_first`,`q_last`), respectively.

Template Parameters

  InputIterator1 | has `Point` as value type.
  InputIterator2 | has `Point` as value type.

Precondition
  All points have the same dimension.

Attention
  If `verbose` is set to \( 1\), \( 2\), or \( 3\) then some, more, or full verbose output of the underlying solver for quadratic programs is written to `stream`, resp.

## Member Function Documentation

## ◆ ambient_dimension()

template<typename Traits >

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

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

If `poly_dist` is \( pd(\emptyset, \emptyset)\), the ambient dimension is \( -1\).

## ◆ insert()

template<typename Traits >
template<class InputIterator1 , class InputIterator2 >

void CGAL::Polytope_distance_d< Traits >::insert | ( | InputIterator1 | p_first,
|  | InputIterator1 | p_last,
|  | InputIterator2 | q_first,
|  | InputIterator2 | q_last
| ) |  |

inserts the points in the range [`p_first`,`p_last`) and [`q_first`,`q_last`) into \( P\) and \( Q\), respectively, and recomputes the (squared) distance.

Template Parameters

  InputIterator1 | has `Point` as value type.
  InputIterator2 | has `Point` as value type.

Precondition
  All points have the same dimension. If `poly_dist` is not \( pd(\emptyset, \emptyset)\), this dimension must be equal to `poly_dist``.ambient_dimension()`.

## ◆ insert_p() [1/2]

template<typename Traits >

void CGAL::Polytope_distance_d< Traits >::insert_p | ( | const Point & | p | ) |

inserts `p` into \( P\).

Precondition
  The dimension of `p` equals `poly_dist``.ambient_dimension()` if `poly_dist` is not \( pd(\emptyset, \emptyset)\).

## ◆ insert_p() [2/2]

template<typename Traits >
template<class InputIterator >

void CGAL::Polytope_distance_d< Traits >::insert_p | ( | InputIterator | p_first,
|  | InputIterator | p_last
| ) |  |

inserts the points in the range [`p_first`,`p_last`) into \( P\) and recomputes the (squared) distance ( \( Q\) remains unchanged).

Template Parameters

  InputIterator | has `Point` as value type.

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

## ◆ insert_q() [1/2]

template<typename Traits >

void CGAL::Polytope_distance_d< Traits >::insert_q | ( | const Point & | q | ) |

inserts `q` into \( Q\).

Precondition
  The dimension of `q` equals `poly_dist``.ambient_dimension()` if `poly_dist` is not \( pd(\emptyset, \emptyset)\).

## ◆ insert_q() [2/2]

template<typename Traits >
template<class InputIterator >

void CGAL::Polytope_distance_d< Traits >::insert_q | ( | InputIterator | q_first,
|  | InputIterator | q_last
| ) |  |

inserts the points in the range [`q_first`,`q_last`) into \( Q\) and recomputes the (squared) distance ( \( P\) remains unchanged).

Template Parameters

  InputIterator | has `Point` as value type.

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

## ◆ is_valid()

template<typename Traits >

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

returns `true`, iff `poly_dist` 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.

An object `poly_dist` is valid, iff \( ldots\)

- `poly_dist` contains all points of its defining set \( P\),
- `poly_dist` is the smallest sphere containing its support set \( S\),
- and \( S\) is minimal, i.e. no support point is redundant.

## ◆ realizing_point_p()

template<typename Traits >

Point CGAL::Polytope_distance_d< Traits >::realizing_point_p | ( |  | ) | const

returns the realizing point of \( P\).

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

Precondition
  \( pd(P,Q)\) is finite.

## ◆ realizing_point_p_coordinates_begin()

template<typename Traits >

Coordinate_iterator CGAL::Polytope_distance_d< Traits >::realizing_point_p_coordinates_begin | ( |  | ) | const

returns an iterator referring to the first coordinate of the realizing point of \( P\).

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.

## ◆ realizing_point_q()

template<typename Traits >

Point CGAL::Polytope_distance_d< Traits >::realizing_point_q | ( |  | ) | const

returns the realizing point of \( Q\).

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

Precondition
  \( pd(P,Q)\) is finite.

## ◆ realizing_point_q_coordinates_begin()

template<typename Traits >

Coordinate_iterator CGAL::Polytope_distance_d< Traits >::realizing_point_q_coordinates_begin | ( |  | ) | const

returns an iterator referring to the first coordinate of the realizing point of \( Q\).

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.

## ◆ set()

template<typename Traits >
template<class InputIterator1 , class InputIterator2 >

void CGAL::Polytope_distance_d< Traits >::set | ( | InputIterator1 | p_first,
|  | InputIterator1 | p_last,
|  | InputIterator2 | q_first,
|  | InputIterator2 | q_last
| ) |  |

sets `poly_dist` to \( pd(P,Q)\) with \( P\) and \( Q\) being the sets of points in the ranges [`p_first`,`p_last`) and [`q_first`,`q_last`), respectively.

Template Parameters

  InputIterator1 | has `Point` as value type.
  InputIterator2 | has `Point` as value type.

Precondition
  All points have the same dimension.

## ◆ set_p()

template<typename Traits >
template<class InputIterator >

void CGAL::Polytope_distance_d< Traits >::set_p | ( | InputIterator | p_first,
|  | InputIterator | p_last
| ) |  |

sets `poly_dist` to \( pd(P,Q)\) with \( P\) being the set of points in the range [`p_first`,`p_last`) ( \( Q\) remains unchanged).

Template Parameters

  InputIterator | has `Point` as value type.

Precondition
  All points in \( P\) have dimension `poly_dist``.ambient_dimension()` if \( Q\) is not empty.

## ◆ set_q()

template<typename Traits >
template<class InputIterator >

void CGAL::Polytope_distance_d< Traits >::set_q | ( | InputIterator | q_first,
|  | InputIterator | q_last
| ) |  |

sets `poly_dist` to \( pd(P,Q)\) with \( Q\) being the set of points in the range [`q_first`,`q_last`) ( \( P\) remains unchanged).

Template Parameters

  InputIterator | has `Point` as value type.

Precondition
  All points in \( Q\) have dimension `poly_dist``.ambient_dimension()` if \( P\) is not empty.

## ◆ squared_distance()

template<typename Traits >

FT CGAL::Polytope_distance_d< Traits >::squared_distance | ( |  | ) | const

returns the squared distance of `poly_dist`, i.e. \( (pd(P,Q))^2\).

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

Precondition
  \( pd(P,Q)\) is finite.

## Friends And Related Function Documentation

## ◆ operator<<()

template<typename Traits >

std::ostream & operator<< | ( | std::ostream & | os,
|  | const Polytope_distance_d< Traits > & | poly_dist
| ) |  |
| related

writes `poly_dist` to output stream `os`.

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

## ◆ operator>>()

template<typename Traits >

std::istream & operator>> | ( | std::istream & | is,
|  | Polytope_distance_d< Traits > poly_dist & |
| ) |  |
| related

reads `poly_dist` from input stream `is`.

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