CGAL 6.1 - Bounding Volumes

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Circle Concept Reference
Reference Manual » Concepts

## Definition

An object `circle` of the class `Circle` is a circle in the two-dimensional Euclidean plane \( \E^2\). Its boundary splits the plane into a bounded and an unbounded side. By definition, an empty `circle` has no boundary and no bounded side, i.e. its unbounded side equals the whole plane \( \E^2\). A `circle` containing exactly one point \( p\) has no bounded side, its boundary is \( \{p\}\), and its unbounded side equals \( \E^2 \setminus \{p\}\).

## Types
typedef unspecified_type | Point
| Point type.
typedef unspecified_type | Distance
| Distance type.

## Creation
void | set ()
| sets `circle` to the empty circle.
void | set (const Point &p)
| sets `circle` to the circle containing exactly `p`.
void | set (const Point &p, const Point &q)
| sets `circle` to the circle with diameter equal to the segment connecting `p` and `q`.
void | set (const Point &p, const Point &q, const Point &r)
| sets `circle` to the circle through `p`, `q`, and `r`.

## Predicates
bool | has_on_unbounded_side (const Point &p) const
| returns `true`, iff `p` lies properly outside of `circle`.
CGAL::Bounded_side | bounded_side (const Point &p) const
| returns `CGAL::ON_BOUNDED_SIDE`, `CGAL::ON_BOUNDARY`, or `CGAL::ON_UNBOUNDED_SIDE` iff `p` lies properly inside, on the boundary, or properly outside of `circle`, resp.
bool | has_on_bounded_side (const Point &p) const
| returns `true`, iff `p` lies properly inside `circle`.
bool | has_on_boundary (const Point &p) const
| returns `true`, iff `p` lies on the boundary of `circle`.
bool | is_empty () const
| returns `true`, iff `circle` is empty (this implies degeneracy).
bool | is_degenerate () const
| returns `true`, iff `circle` is degenerate, i.e. if `circle` is empty or equal to a single point.

## Additional Operations for Checking
bool | operator== (const Circle &circle2) const
| returns `true`, iff `circle` and `circle2` are equal.
Point | center () const
| returns the center of `circle`.
Distance | squared_radius () const
| returns the squared radius of `circle`.

## I/O
std::ostream & | operator<< (std::ostream &os, const Circle &circle)
| writes `circle` to output stream `os`.

## Member Typedef Documentation

## ◆ Distance

typedef unspecified_type Circle::Distance

Distance type.

The function `squared_radius()` (see below) returns an object of this type.

Note
  Only needed, if the member function `is_valid()` of `Min_circle_2` is used.

## Member Function Documentation

## ◆ bounded_side()

CGAL::Bounded_side Circle::bounded_side | ( | const Point & | p | ) | const

returns `CGAL::ON_BOUNDED_SIDE`, `CGAL::ON_BOUNDARY`, or `CGAL::ON_UNBOUNDED_SIDE` iff `p` lies properly inside, on the boundary, or properly outside of `circle`, resp.

Note
  Only needed, if the corresponding predicate of `Min_circle_2` is used.

## ◆ center()

Point Circle::center | ( |  | ) | const

returns the center of `circle`.

Note
  Only needed, if the member function `is_valid()` of `Min_circle_2` is used.

## ◆ has_on_boundary()

bool Circle::has_on_boundary | ( | const Point & | p | ) | const

returns `true`, iff `p` lies on the boundary of `circle`.

Note
  Only needed, if the corresponding predicate of `Min_circle_2` is used.

## ◆ has_on_bounded_side()

bool Circle::has_on_bounded_side | ( | const Point & | p | ) | const

returns `true`, iff `p` lies properly inside `circle`.

Note
  Only needed, if the corresponding predicate of `Min_circle_2` is used.

## ◆ is_degenerate()

bool Circle::is_degenerate | ( |  | ) | const

returns `true`, iff `circle` is degenerate, i.e. if `circle` is empty or equal to a single point.

Note
  Only needed, if the corresponding predicate of `Min_circle_2` is used.

## ◆ is_empty()

bool Circle::is_empty | ( |  | ) | const

returns `true`, iff `circle` is empty (this implies degeneracy).

Note
  Only needed, if the corresponding predicate of `Min_circle_2` is used.

## ◆ operator==()

bool Circle::operator== | ( | const Circle & | circle2 | ) | const

returns `true`, iff `circle` and `circle2` are equal.

Note
  Only needed, if the member function `is_valid()` of `Min_circle_2` is used.

## ◆ set() [1/2]

void Circle::set | ( | const Point & | p,
|  | const Point & | q
| ) |  |

sets `circle` to the circle with diameter equal to the segment connecting `p` and `q`.

The algorithm guarantees that `set()` is never called with two equal points.

## ◆ set() [2/2]

void Circle::set | ( | const Point & | p,
|  | const Point & | q,
|  | const Point & | r
| ) |  |

sets `circle` to the circle through `p`, `q`, and `r`.

The algorithm guarantees that `set()` is never called with three collinear points.

## ◆ squared_radius()

Distance Circle::squared_radius | ( |  | ) | const

returns the squared radius of `circle`.

Note
  Only needed, if the member function `is_valid()` of `Min_circle_2` is used.