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## PartitionTraits_2

### Definition

The polygon partitioning functions are each parameterized by a traits class that defines the primitives used in the algorithms. Many requirements are common to all traits classes. The concept PartitionTraits_2 defines this common set of requirements.

### Types

PartitionTraits_2::Point_2
| The point type on which the partitioning algorithm operates.
PartitionTraits_2::Polygon_2
| The polygon type to be created by the partitioning algorithm. For testing the validity postcondition of the partition, this type should provide a nested type Vertex_const_iterator that is the type of the iterator over the polygon vertices and member functions Vertex_const_iterator vertices_begin() and Vertex_const_iterator vertices_end().

PartitionTraits_2::Less_xy_2
| Predicate object type that compares Point_2s lexicographically. Must provide bool operator()(Point_2 p, Point_2 q) where true is returned iff p <xy q. We have p<xyq, iff px < qx or px = qx and py < qy, where px and py denote the x and y coordinates of point p, respectively.
PartitionTraits_2::Less_yx_2
| Same as Less_xy_2 with the roles of x and y interchanged.
PartitionTraits_2::Left_turn_2
| Predicate object type that provides bool operator()(Point_2 p,Point_2 q,Point_2 r), which returns true iff r lies to the left of the oriented line through p and q.
PartitionTraits_2::Orientation_2
| Predicate object type that provides CGAL::Orientation operator()(Point_2 p, Point_2 q, Point_2 r) that returns CGAL::LEFT_TURN, if r lies to the left of the oriented line l defined by p and q, returns CGAL::RIGHT_TURN if r lies to the right of l, and returns CGAL::COLLINEAR if r lies on l.
PartitionTraits_2::Compare_y_2
| Predicate object type that provides CGAL::Comparision_result operator()(Point_2 p, Point_2 q) to compare the y values of two points. The operator must return CGAL::SMALLER if py < qy, CGAL::LARGER if py > qy and CGAL::EQUAL if py = qy.
PartitionTraits_2::Compare_x_2
| The same as Compare_y_2, except that x coordinates are compared instead of y.

### Creation

A copy constructor and default constructor are required.

PartitionTraits_2 traits;

PartitionTraits_2 traits ( & tr);

### Operations

The following functions that create instances of the above predicate object types must exist.

Less_yx_2 | traits.less_yx_2_object ()
Less_xy_2 | traits.less_xy_2_object ()
Left_turn_2 | traits.left_turn_2_object ()
Orientation_2 | traits.orientation_2_object ()
Compare_y_2 | traits.compare_y_2_object ()
Compare_x_2 | traits.compare_x_2_object ()

### Has Models

CGAL::Partition_traits_2<R>

### See Also

CGAL::approx_convex_partition_2
CGAL::greene_approx_convex_partition_2
CGAL::optimal_convex_partition_2
CGAL::y_monotone_partition_2

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The CGAL Project . Tue, December 21, 2004 .