CGAL 6.1 - Inscribed Areas

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Modules | Classes | Functions
Reference Manual

##

Michael Hoffmann and Eli Packer
This package provides algorithms for computing inscribed areas. The algorithms for computing inscribed areas are: the largest inscribed k-gon (area or perimeter) of a convex point set and the largest inscribed iso-rectangle.
Introduced in: CGAL 1.1
BibTeX: cgal:hp-ia-25b
License: GPL
Windows Demos: 2D Inscribed k-gon as part of Polygon demo, 2D Largest Empty Rectangle

## Classified Reference Pages

- `CGAL::maximum_area_inscribed_k_gon_2()`
- `CGAL::maximum_perimeter_inscribed_k_gon_2()`
- `CGAL::extremal_polygon_2()`
- `CGAL::Largest_empty_iso_rectangle_2<T>`
- `CGAL::Extremal_polygon_area_traits_2<K>`
- `CGAL::Extremal_polygon_perimeter_traits_2<K>`
- `ExtremalPolygonTraits_2`
- `LargestEmptyIsoRectangleTraits_2`

## Modules
| Concepts

## Classes
struct | CGAL::Extremal_polygon_area_traits_2< K >
| This is an advanced class. More...
struct | CGAL::Extremal_polygon_perimeter_traits_2< K >
| This is an advanced class. More...
class | CGAL::Largest_empty_iso_rectangle_2< T >
| Given a set of points in the plane, the class `Largest_empty_iso_rectangle_2` is a data structure that maintains an iso-rectangle with the largest area among all iso-rectangles that are inside a given bounding box( iso-rectangle), and that do not contain any point of the point set. More...

## Functions
template<class RandomAccessIterator , class OutputIterator , class Traits >
OutputIterator | CGAL::extremal_polygon_2 (RandomAccessIterator points_begin, RandomAccessIterator points_end, int k, OutputIterator o, const Traits &t)
| computes a maximal (as specified by `t`) inscribed `k`-gon of the convex polygon described by [`points_begin`, `points_end`), writes its vertices to `o` and returns the past-the-end iterator of this sequence.
template<class RandomAccessIterator , class OutputIterator >
OutputIterator | CGAL::maximum_area_inscribed_k_gon_2 (RandomAccessIterator points_begin, RandomAccessIterator points_end, int k, OutputIterator o)
| computes a maximum area inscribed `k`-gon of the convex polygon described by [`points_begin`, `points_end`), writes its vertices to `o` and returns the past-the-end iterator of this sequence.
template<class RandomAccessIterator , class OutputIterator >
OutputIterator | CGAL::maximum_perimeter_inscribed_k_gon_2 (RandomAccessIterator points_begin, RandomAccessIterator points_end, int k, OutputIterator o)
| computes a maximum perimeter inscribed `k`-gon of the convex polygon described by `[points_begin, points_end)`, writes its vertices to `o` and returns the past-the-end iterator of this sequence.

## Function Documentation

## ◆ extremal_polygon_2()

template<class RandomAccessIterator , class OutputIterator , class Traits >

OutputIterator CGAL::extremal_polygon_2 | ( | RandomAccessIterator | points_begin,
|  | RandomAccessIterator | points_end,
|  | int | k,
|  | OutputIterator | o,
|  | const Traits & | t
| ) |  |

`#include <CGAL/extremal_polygon_2.h>`

computes a maximal (as specified by `t`) inscribed `k`-gon of the convex polygon described by [`points_begin`, `points_end`), writes its vertices to `o` and returns the past-the-end iterator of this sequence.

The function `extremal_polygon_2()` computes a maximal `k`-gon that can be inscribed into a given convex polygon. The criterion for maximality and some basic operations have to be specified in an appropriate traits class parameter.

Precondition
  the - at least three - points denoted by the range `[points_begin, points_end)` form the boundary of a convex polygon (oriented clock- or counterclockwise).
  `k >= t.min_k()`.

Template Parameters

  Traits | must be a model for `ExtremalPolygonTraits_2`.
  RandomAccessIterator | must be an iterator with value type `Traits::Point_2`.
  OutputIterator | must accepts dereference/assignments of `Traits::Point_2`.

See also
  `CGAL::maximum_area_inscribed_k_gon_2()`
  `CGAL::maximum_perimeter_inscribed_k_gon_2()`
  `ExtremalPolygonTraits_2`

Implementation

The implementation uses monotone matrix search [1] and has a worst case running time of \(O(k \cdot n + n \cdot \log n)\), where \( n\) is the number of vertices in \( P\).

## ◆ maximum_area_inscribed_k_gon_2()

template<class RandomAccessIterator , class OutputIterator >

OutputIterator CGAL::maximum_area_inscribed_k_gon_2 | ( | RandomAccessIterator | points_begin,
|  | RandomAccessIterator | points_end,
|  | int | k,
|  | OutputIterator | o
| ) |  |

`#include <CGAL/extremal_polygon_2.h>`

computes a maximum area inscribed `k`-gon of the convex polygon described by [`points_begin`, `points_end`), writes its vertices to `o` and returns the past-the-end iterator of this sequence.

Computes a maximum area `k`-gon \( P_k\) that can be inscribed into a given convex polygon \( P\). Note that

- \( P_k\) is not unique in general, but it can be chosen in such a way that its vertices form a subset of the vertex set of \( P\) and
- the vertices of a maximum area `k`-gon, where the `k` vertices are to be drawn from a planar point set \( S\), lie on the convex hull of \( S\) i.e. a convex polygon.

Precondition
  the - at least three - points denoted by the range `[points_begin, points_end)` form the boundary of a convex polygon (oriented clock- or counterclockwise).
  `k >= 3`.

Template Parameters

  RandomAccessIterator | must be an iterator with value type `K::Point_2` where `K` is a model of `Kernel`.
  OutputIterator | must accepts dereference/assignments of `Traits::Point_2`.

See also
  `CGAL::maximum_perimeter_inscribed_k_gon_2()`
  `ExtremalPolygonTraits_2`
  `CGAL::Extremal_polygon_area_traits_2<K>`
  `CGAL::Extremal_polygon_perimeter_traits_2<K>`
  `CGAL::extremal_polygon_2()`

Implementation

The implementation uses monotone matrix search [1] and has a worst case running time of \(O(k \cdot n + n \cdot \log n)\), where \( n\) is the number of vertices in \( P\).

Example

The following code generates a random convex polygon `p` with ten vertices and computes the maximum area inscribed five-gon of `p`.

File Inscribed_areas/extremal_polygon_2_area.cpp

#include <CGAL/Simple_cartesian.h>
#include <CGAL/Polygon_2.h>
#include <CGAL/point_generators_2.h>
#include <CGAL/random_convex_set_2.h>
#include <CGAL/extremal_polygon_2.h>
#include <iostream>
#include <vector>
typedef double FT;
typedef CGAL::Simple_cartesian<FT> Kernel;
typedef Kernel::Point_2 Point;
typedef std::vector<int> Index_cont;
typedef CGAL::Polygon_2<Kernel> Polygon_2;
typedef CGAL::Random_points_in_square_2<Point> Generator;
int main() {
int n = 10;
int k = 5;
// generate random convex polygon:
Polygon_2 p;
CGAL::random_convex_set_2(n, std::back_inserter(p), Generator(1));
std::cout << "Generated Polygon:\n" << p << std::endl;
// compute maximum area incribed k-gon of p:
Polygon_2 k_gon;
CGAL::maximum_area_inscribed_k_gon_2(
p.vertices_begin(), p.vertices_end(), k, std::back_inserter(k_gon));
std::cout << "Maximum area " << k << "-gon:\n"
<< k_gon << std::endl;
return 0;
}
Kernel::Point_2
CGAL::maximum_area_inscribed_k_gon_2
OutputIterator maximum_area_inscribed_k_gon_2(RandomAccessIterator points_begin, RandomAccessIterator points_end, int k, OutputIterator o)
computes a maximum area inscribed k-gon of the convex polygon described by [points_begin,...
Kernel
CGAL::Simple_cartesian

Examples
  Inscribed_areas/extremal_polygon_2_area.cpp.

## ◆ maximum_perimeter_inscribed_k_gon_2()

template<class RandomAccessIterator , class OutputIterator >

OutputIterator CGAL::maximum_perimeter_inscribed_k_gon_2 | ( | RandomAccessIterator | points_begin,
|  | RandomAccessIterator | points_end,
|  | int | k,
|  | OutputIterator | o
| ) |  |

`#include <CGAL/extremal_polygon_2.h>`

computes a maximum perimeter inscribed `k`-gon of the convex polygon described by `[points_begin, points_end)`, writes its vertices to `o` and returns the past-the-end iterator of this sequence.

The function `maximum_perimeter_inscribed_k_gon_2()` computes a maximum perimeter `k`-gon \( P_k\) that can be inscribed into a given convex polygon \( P\). Note that

- \( P_k\) is not unique in general, but it can be chosen in such a way that its vertices form a subset of the vertex set of \( P\) and
- the vertices of a maximum perimeter `k`-gon, where the `k` vertices are to be drawn from a planar point set \( S\), lie on the convex hull of \( S\) i.e. a convex polygon.

Precondition
  the - at least three - points denoted by the range `[points_begin, points_end)` form the boundary of a convex polygon (oriented clock- or counterclockwise).
  `k >= 2`.

Template Parameters

  RandomAccessIterator | must be an iterator with value type `K::Point_2` where `K` is a model for `Kernel`.
  OutputIterator | must accepts dereference/assignments of `Traits::Point_2`.

There must be a global function `K::FT CGAL::sqrt(K::FT)` defined that computes the squareroot of a number.

See also
  `CGAL::maximum_area_inscribed_k_gon_2()`
  `ExtremalPolygonTraits_2`
  `CGAL::Extremal_polygon_area_traits_2<K>`
  `CGAL::Extremal_polygon_perimeter_traits_2<K>`
  `CGAL::extremal_polygon_2()`

Implementation

The implementation uses monotone matrix search [1] and has a worst case running time of \(O(k \cdot n + n \cdot \log n)\), where \( n\) is the number of vertices in \( P\).

Example

The following code generates a random convex polygon `p` with ten vertices and computes the maximum perimeter inscribed five-gon of `p`.

File Inscribed_areas/extremal_polygon_2_perimeter.cpp

#include <CGAL/Simple_cartesian.h>
#include <CGAL/Polygon_2.h>
#include <CGAL/point_generators_2.h>
#include <CGAL/random_convex_set_2.h>
#include <CGAL/extremal_polygon_2.h>
#include <iostream>
#include <vector>
typedef double FT;
typedef CGAL::Simple_cartesian<FT> Kernel;
typedef Kernel::Point_2 Point;
typedef std::vector<int> Index_cont;
typedef CGAL::Polygon_2<Kernel> Polygon_2;
typedef CGAL::Random_points_in_square_2<Point> Generator;
int main() {
int n = 10;
int k = 5;
// generate random convex polygon:
Polygon_2 p;
CGAL::random_convex_set_2(n, std::back_inserter(p), Generator(1));
std::cout << "Generated Polygon:\n" << p << std::endl;
// compute maximum perimeter incribed k-gon of p:
Polygon_2 k_gon;
CGAL::maximum_perimeter_inscribed_k_gon_2(
p.vertices_begin(), p.vertices_end(), k, std::back_inserter(k_gon));
std::cout << "Maximum perimeter " << k << "-gon:\n"
<< k_gon << std::endl;
return 0;
}
CGAL::maximum_perimeter_inscribed_k_gon_2
OutputIterator maximum_perimeter_inscribed_k_gon_2(RandomAccessIterator points_begin, RandomAccessIterator points_end, int k, OutputIterator o)
computes a maximum perimeter inscribed k-gon of the convex polygon described by [points_begin,...

Examples
  Inscribed_areas/extremal_polygon_2_perimeter.cpp.