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>.

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

Hashable if Kernel is a cartesian kernel and if Kernel::FT is Hashable

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< Kernel >	operator- (const Point_2< Kernel > &p, const Point_2< Kernel > &q)
	returns the difference vector between q and p. More...
Point_2< Kernel >	operator+ (const Point_2< Kernel > &p, const Vector_2< Kernel > &v)
	returns the point obtained by translating p by the vector v.
Point_2< Kernel >	operator- (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.
Point_2< Kernel >	transform (const Aff_transformation_2< Kernel > &t) const
	returns the point obtained by applying t on p.

Constructor & Destructor Documentation

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 != 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.

Member Function Documentation

cartesian()

template<typename Kernel >

Kernel::FT CGAL::Point_2< Kernel >::cartesian

(

int

i

)

const

returns the i'th Cartesian coordinate of p.

Precondition

0 <= i <= 1.

homogeneous()

template<typename Kernel >

Kernel::RT CGAL::Point_2< Kernel >::homogeneous

(

int

i

)

const

returns the i'th homogeneous coordinate of p.

Precondition

0 <= i <= 2.

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 <= i <= 1.

Friends And Related Function Documentation

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.