CGAL 6.2 - 2D Arrangements

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CGAL::Arr_polycurve_traits_2< SubcurveTraits_2 > Class Template Reference
Reference Manual » Geometry Traits Classes

`#include <CGAL/Arr_polycurve_traits_2.h>`

## Definition

template<typename SubcurveTraits_2>
class CGAL::Arr_polycurve_traits_2< SubcurveTraits_2 >

Note: The `SubcurveTraits_2` can comprise of Line_segments, Conic_arcs, Circular_arc, Bezier_curves, or Linear_curves.

A portion or a part of any of the above mentioned geometric traits is called a subcurve.

The traits class `Arr_polycurve_traits_2` handles piecewise curves that are not necessarily linear, such as conic arcs, circular arcs, Bezier curves, or line segments. We call such a compound curve a polycurve. A polycurve is a chain of subcurves, where each two neighboring subcurves in the chain share a common endpoint; that is, the polycurve is continuous. Furthermore, the target of the \(i\)-th segment of a polycurve has to coincide with the source of the \(i+1\)-st segment; that is, the polycurve has to be well-oriented. Note that it is possible to construct general polycurves that are neither continuous nor well-oriented, as it is impossible to enforce this precondition (using the set of predicates required by the relevant concepts, see below). However, such polycurves cannot be used for the actual computation of arrangements. The traits class template exploits the functionality of the `SubcurveTraits_2` template-parameter to handle the subcurves that compose the polycurve.

The type substituting the template parameter `SubcurveTraits_2` when the template Arr_polycurve_traits_2 is instantiated must be a model of the concepts

- `AosTraits_2` and
- `AosDirectionalXMonotoneTraits_2`.

If, in addition, the SubcurveTraits_2 models the concept `AosApproximatePointTraits_2` then `Arr_polycurve_traits_2` models this concept as well. The same holds for the concept `AosOpenBoundaryTraits_2`. If no type is provided, then `Arr_segment_traits_2` (instantiated with `Exact_predicates_exact_constructions_kernel` as the kernel) is used. Otherwise, `Arr_algebraic_segment_traits_2<Coefficient>`, `Arr_Bezier_curve_traits_2<RatKernel, AlgKernel, NtTraits>`, `Arr_circle_segment_traits_2<Kernel>`, `Arr_conic_traits_2<RatKernel, AlgKernel, NtTraits>`, `Arr_linear_traits_2<Kernel>`, `Arr_non_caching_segment_traits_2<Kernel>`, `Arr_segment_traits_2<Kernel>`, `Arr_rational_function_traits_2<AlgebraicKernel_d_1>`, or any other model of the concepts above can be used.

The number type used by the injected subcurve traits should support exact rational arithmetic (that is, the number type should support the arithmetic operations \(+\), \(-\), \(\times\) and \(\div\) carried out without loss of precision), in order to avoid robustness problems, although other inexact number types could be used at the user's own risk.

A polycurve that comprises \(n > 0\) subcurves has \(n+1\) subcurve end-points, and they are represented as objects of type `SubcurveTraits_2::Point_2`. Since the notion of a vertex is reserved to 0-dimensional elements of an arrangement, we use, in this context, the notion of points in order to refer to the vertices of a polycurve. For example, an arrangement induced by a single non-self intersecting polycurve has exactly two vertices regardless of the number of subcurve end-points. Finally, the types `Subcurve_2` and `X_monotone_subcurve_2` nested in `Arr_polycurve_traits_2` are nothing but `SubcurveTraits_2::Curve_2` and `SubcurveTraits_2::X_monotone_curve_2`, respectively.

A note on Backwards compatibility
In CGAL version 4.2 (and earlier) any object of the `X_monotone_curve_2` type nested in `Arr_polycurve_traits_2` which in that version was called `Arr_polyline_tratis_2` maintained a direction invariant; namely, its vertices were ordered in an ascending lexicographical \(xy\)-order. This restriction is no longer imposed and `X_monotone_curve_2` can be now directed either from right-to-left or left-to-right. If you wish to maintain a left-to-right orientations of the \(x\)-monotone polycurve, set the macro `CGAL_ALWAYS_LEFT_TO_RIGHT` to 1 before any CGAL header is included.

Is model of
  `AosTraits_2`
  `AosDirectionalXMonotoneTraits_2`
  `AosApproximatePointTraits_2` (if the type that substitutes the template parameter `SubcurveTraits_2` models the concept as well)

See also
  `Arr_algebraic_segment_traits_2<Coefficient>`
  `Arr_Bezier_curve_traits_2<RatKernel, AlgKernel, NtTraits>`
  `Arr_circle_segment_traits_2<Kernel>`
  `Arr_conic_traits_2<RatKernel, AlgKernel, NtTraits>`
  `Arr_linear_traits_2<Kernel>`
  `Arr_non_caching_segment_traits_2<Kernel>`
  `Arr_segment_traits_2<Kernel>`
  `Arr_rational_function_traits_2<AlgebraicKernel_d_1>`
  `CGAL_ALWAYS_LEFT_TO_RIGHT`

Examples
  Arrangement_on_surface_2/polycurve_bezier.cpp, Arrangement_on_surface_2/polycurve_circular_arc.cpp, and Arrangement_on_surface_2/polycurve_conic.cpp.

## Classes
class | Construct_curve_2
| Construction functor of a general (not necessarily \(x\)-monotone) polycurve. More...
class | Construct_x_monotone_curve_2
| Construction functor of \(x\)-monotone polycurve. More...
class | Curve_2
| The `Curve_2` type nested in the `Arr_polycurve_traits_2` represents general continuous piecewise-linear subcurves (a polycurve can be self-intersecting) and support their construction from range of subcurves. More...
class | Make_x_monotone_2
| subdivides a given subcurve into \(x\)-monotone subcurves and isolated points, and insert them into an output container. More...
class | Number_of_points_2
| Function object which returns the number of subcurve end-points of a polycurve. More...
class | Push_back_2
| Functor to augment a polycurve by either adding a vertex or a subcurve at the back. More...
class | Push_front_2
| Functor to augment a polycurve by either adding a vertex or a subcurve at the front. More...
class | Trim_2
class | X_monotone_curve_2
| The `X_monotone_curve_2` class nested within the polycurve traits is used to represent \(x\)-monotone piecewise linear subcurves. More...

## Types
typedef SubcurveTraits_2::Point_2 | Point_2
typedef SubcurveTraits_2::Curve_2 | Subcurve_2
typedef SubcurveTraits_2::X_monotone_curve_2 | X_monotone_subcurve_2

## Accessing Functor Objects
Construct_curve_2 | construct_curve_2_object () const
Construct_x_monotone_curve_2 | construct_x_monotone_curve_2_object () const
Number_of_points_2 | number_of_points_2_object () const
Push_back_2 | push_back_2_object () const
Push_front_2 | push_front_2_object () const
Make_x_monotone_2 | make_x_monotone_2_object () const