CGAL 6.1 - 2D Arrangements

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CGAL::Arr_algebraic_segment_traits_2< Coefficient >::Point_2 Class Reference

`#include <CGAL/Arr_algebraic_segment_traits_2.h>`

## Definition

template<typename Coefficient>
class CGAL::Arr_algebraic_segment_traits_2< Coefficient >::Point_2

A model of the `AosBasicTraits_2::Point_2` concept.

Represents points in \(\mathbb{R}^2\). Intersection points of algebraic curves are in general non-rational, so we need a data structure that is capable of representing arbitrary points with algebraic coordinates.

The traits class represents algebraic coordinates by the type `Algebraic_real_1`, which is a model of the `AlgebraicReal_1` concept. A point \(p\) is stored by a triple \((x,cv,arcno)\), where \(x\) is the \(x\)-coordinate of a point, \(cv\) is an instance of `Curve_2` that contains the point, (and has no vertical line at \(x\)), and \(arcno\) is an `int`, denoting that \(p\) is met as the \(arcno\)-th point when shooting a vertical ray at \(x\), starting from \(-\infty\) (where counting starts with \(0\)).

In addition to the methods listed below, the copy constructor and assignment operator for `Point_2` objects are also supported.

The functor `Construct_point_2` constructs `Point_2` instances.

## Modifiers
Algebraic_real_1 | x () const
| returns the \(x\)-coordinate of `p`.
Algebraic_real_1 | y () const
| returns the \(y\)-coordinates of `p`.
Curve_2 | curve () const
| returns a `Curve_2` instance that `p`is part of.
int | arcno () const
| returns the arc number of `p`.
std::pair< double, double > | to_double () const
| returns double-approximations of the \(x\)- and \(y\)-coordinates.

## Member Function Documentation

## ◆ y()

template<typename Coefficient >

Algebraic_real_1 CGAL::Arr_algebraic_segment_traits_2< Coefficient >::Point_2::y | ( |  | ) | const

returns the \(y\)-coordinates of `p`.

Attention: As described above, points are not stored by their \(y\)-coordinate in `Algebraic_real_1` representation. In fact, this representation must be computed on demand, and might become quite costly for points defined by high-degree polynomials. Therefore, it is recommended to avoid to call this function as much as possible.