CGAL 6.1.2 - Optimal Distances: WidthTraits_3 Concept Reference

CGAL 6.1.2 - Optimal Distances

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WidthTraits_3 Concept Reference
Reference Manual » Concepts

## Definition

This concept defines the requirements for traits classes of `CGAL::Width_3<Traits>`.

Operations

Whatever the coordinates of the points are, it is required for the width-algorithm to have access to the homogeneous representation of points.

Has models
  `CGAL::Width_default_traits_3`

See also
  `CGAL::Width_3<Traits>`

## Related Functions
(Note that these are not member functions.)
Point_3 | make_point (const RT &hx, const RT &hy, const RT &hz, const RT &hw) const
| returns a point of type `Point_3` with homogeneous coordinates \( hx\), \( hy\), \( hz\) and \( hw\).
Plane_3 | make_plane (const RT &a, const RT &b, const RT &c, const RT &d) const
| returns a plane of type `Plane_3` with coefficients \( a\), \( b\), \( c\) and \( d\).
Vector_3 | make_vector (const RT &a, const RT &b, const RT &c) const
| returns a vector of type `Vector_3` with the four homogeneous coefficients \( a\), \( b\), \( c\) and 1.

## Types
Note If you want to compute the width of a polyhedron then you have to make sure that the point type in the traits class and the point type in the polyhedron class are the same! The same holds for `Traits::Plane_3` and `Polyhedron::Plane_3`.
typedef unspecified_type | Point_3
| The point type.
typedef unspecified_type | Plane_3
| The plane type.
typedef unspecified_type | Vector_3
| The vector type.
typedef unspecified_type | ChullTraits
| The traits class for using the convex hull algorithm.
typedef unspecified_type | RT
| Ring type numbers.

## Creation
Only a default constructor is required.
| WidthTraits_3 ()
RT | get_hx (const Point_3 &p) const
| returns the homogeneous \( x\)-coordinate of point \( p\).
RT | get_hy (const Point_3 &p) const
| returns the homogeneous \( y\)-coordinate of point \( p\).
RT | get_hz (const Point_3 &p) const
| returns the homogeneous \( z\)-coordinate of point \( p\).
RT | get_hw (const Point_3 &p) const
| returns the homogenizing coordinate of point \( p\).
void | get_point_coordinates (const Point_3 &p, RT &px, RT &py, RT &pz, RT &ph) const
| returns all homogeneous coordinates of point \( p\) at once.
RT | get_a (const Plane_3 &f) const
| returns the first coefficient of plane \( f\).
RT | get_b (const Plane_3 &f) const
| returns the second coefficient of plane \( f\).
RT | get_c (const Plane_3 &f) const
| returns the third coefficient of plane \( f\).
RT | get_d (const Plane_3 &f) const
| returns the fourth coefficient of plane \( f\).
void | get_plane_coefficients (const Plane_3 &f, RT &a, RT &b, RT &c, RT &d) const
| returns all four plane coefficients of \( f\) at once.

## Member Typedef Documentation

## ◆ ChullTraits

typedef unspecified_type WidthTraits_3::ChullTraits

The traits class for using the convex hull algorithm.

It must be a model of the concept ConvexHullTraits_3. This class is used only if the width is computed from a set of points.

## ◆ Plane_3

typedef unspecified_type WidthTraits_3::Plane_3

The plane type.

Access to the coefficients of the plane is made via the `get_...()` functions. Constructing a plane is done with the `make_plane()` operation.

## ◆ Point_3

typedef unspecified_type WidthTraits_3::Point_3

The point type.

The (in)equality tests must be available. Access to the point coordinates is done via the `get_...()` functions. Constructing a point is done with the `make_point( )` operation.

## ◆ RT

typedef unspecified_type WidthTraits_3::RT

Ring type numbers.

Internally all numbers are treated as ring type numbers, i.e., neither \( /\)-operator nor \( \sqrt{.}\) nor other inexact operations are used. But because the algorithm does not use any divisions, but multiplication instead, the numbers can get really big. Therefore it is recommended to use a ring type number, that provides values of arbitrary length. Furthermore it is assumed that the underlying number type of `Point_3`, `Plane_3` and `Vector_3` equals `RT`.

## ◆ Vector_3

typedef unspecified_type WidthTraits_3::Vector_3

The vector type.

There is no need to access the coefficients of a vector; only constructing is required and is done with the `make_vector` operation.