CGAL 6.0.2 - 2D Visibility

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CGAL::Simple_polygon_visibility_2< Arrangement_2_, RegularizationCategory > Class Template Reference
Visibility_2 Reference » Classes

`#include <CGAL/Simple_polygon_visibility_2.h>`

## Definition

template<typename Arrangement_2_, typename RegularizationCategory = Tag_true>
class CGAL::Simple_polygon_visibility_2< Arrangement_2_, RegularizationCategory >

This class is a model of the concept `Visibility_2` can answer visibility queries within a simple polygon with no holes.

This class implements the algorithm of B.Joe and R.B.Simpson [4]. The algorithm is a modification and extension of the linear time algorithm of Lee [5]. It computes the visibility region from a viewpoint that is in the interior or on the boundary of the polygon.

While scanning the boundary the algorithm uses a stack to manipulate the vertices, and ultimately yields the visibility region. For each scanned edge, at most 2 points are pushed onto the stack. Overall, at most 2 \( n \) points are pushed or popped. Thus, the time and space complexities of the algorithm are \(O(n)\)$ even in case of degeneracies such as needles, where \( n \) is the number of the vertices of the polygon.

Template Parameters

  Arrangement_2_ | is the type used to represent the input environment. It must be an instance of `CGAL::Arrangement_2`, where its `CGAL::Arrangement_2::Traits_2` must be an instance of `CGAL::Arr_segment_traits_2`, or of `CGAL::Arr_non_caching_segment_traits_2`.
  RegularizationCategory | indicates whether the output should be regularized. It can be specified by one of the following: `#Tag_true` or `#Tag_false`, where `#Tag_false` is the default value.

Is model of
  `Visibility_2`

See also
  `CGAL::Rotational_sweep_visibility_2`
  `CGAL::Triangular_expansion_visibility_2`

Examples
  Visibility_2/simple_polygon_visibility_2.cpp.

## Types
typedef Arrangement_2 | Arrangement_2
| The arrangement type is used for input.

## Tags
typedef RegularizationCategory | Regularization_category
| identifies whether the regularized visibility area is computed (either `#Tag_true` or `#Tag_false`).
typedef Tag_false | Supports_general_polygon_category
| See Visibility_2::Supports_general_polygon_category.
typedef Tag_true | Supports_simple_polygon_category
| See Visibility_2::Supports_simple_polygon_category.

## Functions
void | attach (const Arrangement_2 &arr)
| Attaches the given arrangement to the visibility object.

## Member Typedef Documentation

## ◆ Regularization_category

template<typename Arrangement_2_ , typename RegularizationCategory = Tag_true>

typedef RegularizationCategory CGAL::Simple_polygon_visibility_2< Arrangement_2_, RegularizationCategory >::Regularization_category

identifies whether the regularized visibility area is computed (either `#Tag_true` or `#Tag_false`).

## Member Function Documentation

## ◆ attach()

template<typename Arrangement_2_ , typename RegularizationCategory = Tag_true>

void CGAL::Simple_polygon_visibility_2< Arrangement_2_, RegularizationCategory >::attach | ( | const Arrangement_2 & | arr | ) |

Attaches the given arrangement to the visibility object.

This operation takes \(O(1)\) as the class does no pre-processing.

In case the object is already attached to another arrangement, the visibility object gets detached before being attached to `arr`.