Ball primitive: a circle in 2D or a sphere in 3D. More...

#include <Ball.h>

Inheritance diagram for Ball:

Public Member Functions
	Ball (const libMesh::Point &c, libMesh::Real r)

	~Ball () override=default

const libMesh::Point &	center () const

libMesh::Real	radius () const

bool	intersect (const LineSegment &line_segment) const override
	Check if a line segment intersects this ball.

Ball	computeBoundingBall () const override
	return the ball itself

libMesh::Sphere	toSphere () const

Private Attributes
libMesh::Point	_c

libMesh::Real	_r

Detailed Description

Ball primitive: a circle in 2D or a sphere in 3D.

Why not just use libMesh::Sphere?

libMesh::Sphere is 3D only; Ball supports both 2D and 3D in a single type.
Ball provides the operations the framework geometries layer needs: intersection with a LineSegment and a tight bounding ball used for fast nearest-neighbor / spatial searches. libMesh::Sphere exposes a different set of surface queries (closest point, normal, above/below surface) that we do not need here.
Ball derives from GeometryBase so every framework geometry primitive can be used through one virtual interface.

If a caller does need the libMesh surface-query interface (e.g. ray tracing), use toSphere() to convert.

Definition at line 34 of file Ball.h.

Constructor & Destructor Documentation

◆ Ball()

Ball::Ball	(	const libMesh::Point &	c,
		libMesh::Real	r
	)

inline

Definition at line 37 of file Ball.h.

37: _c(c), _r(r) {}

Ball::_r

libMesh::Real _r

Definition Ball.h:60

Ball::_c

libMesh::Point _c

Definition Ball.h:59

◆ ~Ball()

Ball::~Ball ( )

overridedefault

Member Function Documentation

◆ center()

const libMesh::Point & Ball::center ( ) const

inline

Definition at line 41 of file Ball.h.

41{ return _c; }

Referenced by AdaptiveRayContainmentCheck::isOutsideBoundingRegion(), and AdaptiveRayContainmentCheck::isOutsideRayBBox().

◆ computeBoundingBall()

Ball Ball::computeBoundingBall ( ) const

overridevirtual

return the ball itself

Implements GeometryBase.

Definition at line 43 of file Ball.C.

{
  return *this;
}

◆ intersect()

bool Ball::intersect ( const LineSegment & line_segment ) const

overridevirtual

Check if a line segment intersects this ball.

Implements GeometryBase.

Definition at line 16 of file Ball.C.

{
  const Point & p0 = line_segment.start();
  const Point & p1 = line_segment.end();
  const Point d = p1 - p0;
  const Point f = p0 - _c;
 
  const Real a = d.norm_sq();
  const Real b = 2.0 * (f * d);
  const Real c = f.norm_sq() - _r * _r;
 
  if (a == 0.0)
    return f.norm_sq() <= _r * _r;
 
  const Real discriminant = b * b - 4.0 * a * c;
  if (discriminant < 0.0)
    return false;
 
  const Real sqrt_disc = std::sqrt(discriminant);
  const Real inv_denom = 1.0 / (2.0 * a);
  const Real t1 = (-b - sqrt_disc) * inv_denom;
  const Real t2 = (-b + sqrt_disc) * inv_denom;
 
  return (t1 >= 0.0 && t1 <= 1.0) || (t2 >= 0.0 && t2 <= 1.0);
}