 CGAL 4.12 - 2D and 3D Linear Geometry Kernel
CGAL::Point_2< Kernel > Class Template Reference

#include <CGAL/Point_2.h>

## Definition

An object p of the class Point_2 is a point in the two-dimensional Euclidean plane $$\E^2$$.

Remember that Kernel::RT and Kernel::FT denote a RingNumberType and a FieldNumberType, respectively. For the kernel model Cartesian<NT>, the two types are the same. For the kernel model Homogeneous<NT>, Kernel::RT is equal to NT, and Kernel::FT is equal to Quotient<NT>.

Operators

The following operations can be applied on points:

Example

The following declaration creates two points with Cartesian double coordinates.

Point_2< Cartesian<double> > p, q(1.0, 2.0);

The variable p is uninitialized and should first be used on the left hand side of an assignment.

p = q;
std::cout << p.x() << " " << p.y() << std::endl;
Is Model Of:
Kernel::Point_2

## Related Functions

(Note that these are not member functions.)

bool operator< (const Point_2< Kernel > &p, const Point_2< Kernel > &q)
returns true iff p is lexicographically smaller than q, i.e. either if p.x() < q.x() or if p.x() == q.x() and p.y() < q.y().

bool operator> (const Point_2< Kernel > &p, const Point_2< Kernel > &q)
returns true iff p is lexicographically greater than q.

bool operator<= (const Point_2< Kernel > &p, const Point_2< Kernel > &q)
returns true iff p is lexicographically smaller or equal to q.

bool operator>= (const Point_2< Kernel > &p, const Point_2< Kernel > &q)
returns true iff p is lexicographically greater or equal to q.

Vector_2< Kerneloperator- (const Point_2< Kernel > &p, const Point_2< Kernel > &q)
returns the difference vector between q and p. More...

Point_2< Kerneloperator+ (const Point_2< Kernel > &p, const Vector_2< Kernel > &v)
returns the point obtained by translating p by the vector v.

Point_2< Kerneloperator- (const Point_2< Kernel > &p, const Vector_2< Kernel > &v)
returns the point obtained by translating p by the vector -v.

## Types

typedef unspecified_type Cartesian_const_iterator
An iterator for enumerating the Cartesian coordinates of a point.

## Creation

Point_2 (const Origin &ORIGIN)
introduces a variable p with Cartesian coordinates $$(0,0)$$.

Point_2 (int x, int y)
introduces a point p initialized to (x,y).

Point_2 (double x, double y)
introduces a point p initialized to (x,y) provided RT supports construction from double.

Point_2 (const Kernel::RT &hx, const Kernel::RT &hy, const Kernel::RT &hw=RT(1))
introduces a point p initialized to (hx/hw,hy/hw). More...

Point_2 (const Kernel::FT &x, const Kernel::FT &y)
introduces a point p initialized to (x,y).

Point_2 (const Kernel::Weighted_point_2 &wp)
introduces a point from a weighted point. More...

## Operations

bool operator== (const Point_2< Kernel > &q) const
Test for equality. More...

bool operator!= (const Point_2< Kernel > &q) const
Test for inequality. More...

Point_2< Kernel > & operator+= (const Vector_2< Kernel > &v)
translates the point by the vector v.

Point_2< Kernel > & operator-= (const Vector_2< Kernel > &v)
translates the point by the vector -v.

## Coordinate Access

There are two sets of coordinate access functions, namely to the homogeneous and to the Cartesian coordinates.

They can be used independently from the chosen kernel model. Note that you do not lose information with the homogeneous representation, because the FieldNumberType is a quotient.

Kernel::RT hx () const
returns the homogeneous $$x$$ coordinate.

Kernel::RT hy () const
returns the homogeneous $$y$$ coordinate.

Kernel::RT hw () const
returns the homogenizing coordinate.

Kernel::FT x () const
returns the Cartesian $$x$$ coordinate, that is hx()/hw().

Kernel::FT y () const
returns the Cartesian $$y$$ coordinate, that is hy()/hw().

## Convenience Operations

The following operations are for convenience and for compatibility with higher dimensional points.

Again they come in a Cartesian and in a homogeneous flavor.

Kernel::RT homogeneous (int i) const
returns the i'th homogeneous coordinate of p. More...

Kernel::FT cartesian (int i) const
returns the i'th Cartesian coordinate of p. More...

Kernel::FT operator[] (int i) const
returns cartesian(i). More...

Cartesian_const_iterator cartesian_begin () const
returns an iterator to the Cartesian coordinates of p, starting with the 0th coordinate.

Cartesian_const_iterator cartesian_end () const
returns an off the end iterator to the Cartesian coordinates of p.

int dimension () const
returns the dimension (the constant 2).

Bbox_2 bbox () const
returns a bounding box containing p. More...

Point_2< Kerneltransform (const Aff_transformation_2< Kernel > &t) const
returns the point obtained by applying t on p.

## ◆ Point_2() [1/2]

template<typename Kernel >
 CGAL::Point_2< Kernel >::Point_2 ( const Kernel::RT & hx, const Kernel::RT & hy, const Kernel::RT & hw = RT(1) )

introduces a point p initialized to (hx/hw,hy/hw).

Precondition
hw $$\neq$$ Kernel::RT(0).

## ◆ Point_2() [2/2]

template<typename Kernel >
 CGAL::Point_2< Kernel >::Point_2 ( const Kernel::Weighted_point_2 & wp )
explicit

introduces a point from a weighted point.

Warning
The explicit keyword is used to avoid accidental implicit conversions between Point_2 and Weighted_point_2.

## ◆ bbox()

template<typename Kernel >
 Bbox_2 CGAL::Point_2< Kernel >::bbox ( ) const

returns a bounding box containing p.

Note that bounding boxes are not parameterized with whatsoever.

## ◆ cartesian()

template<typename Kernel >
 Kernel::FT CGAL::Point_2< Kernel >::cartesian ( int i ) const

returns the i'th Cartesian coordinate of p.

Precondition
$$0\leq i \leq1$$.

## ◆ homogeneous()

template<typename Kernel >
 Kernel::RT CGAL::Point_2< Kernel >::homogeneous ( int i ) const

returns the i'th homogeneous coordinate of p.

Precondition
$$0\leq i \leq2$$.

## ◆ operator!=()

template<typename Kernel >
 bool CGAL::Point_2< Kernel >::operator!= ( const Point_2< Kernel > & q ) const

Test for inequality.

The point can be compared with ORIGIN.

## ◆ operator==()

template<typename Kernel >
 bool CGAL::Point_2< Kernel >::operator== ( const Point_2< Kernel > & q ) const

Test for equality.

Two points are equal, iff their $$x$$ and $$y$$ coordinates are equal. The point can be compared with ORIGIN.

## ◆ operator[]()

template<typename Kernel >
 Kernel::FT CGAL::Point_2< Kernel >::operator[] ( int i ) const

returns cartesian(i).

Precondition
$$0\leq i \leq1$$.

## ◆ operator-()

template<typename Kernel >
 Vector_2< Kernel > operator- ( const Point_2< Kernel > & p, const Point_2< Kernel > & q )
related

returns the difference vector between q and p.

You can substitute ORIGIN for either p or q, but not for both.