CGAL::Plane_3<R>

Definition

³

h : a x + b y + c z + d = 0

The plane splits $$ ³ in a positive and a negative side. A point $$p with Cartesian coordinates $$(px, py, pz) is on the positive side of h, iff a px + b py +c pz + d > 0, it is on the negative side, iff a px + b py +c pz + d < 0.

Creation

Plane_3<R> h ( R::RT a, R::RT b, R::RT c, R::RT d);
	creates a plane h defined by the equation a px + b py + c pz + d = 0. Notice that h is degenerate if a = b = c.
Plane_3<R> h ( Point_3<R> p, Point_3<R> q, Point_3<R> r);
	creates a plane h passing through the points p, q and r. The plane is oriented such that p, q and r are oriented in a positive sense (that is counterclockwise) when seen from the positive side of h. Notice that h is degenerate if the points are collinear.
Plane_3<R> h ( Point_3<R> p, Direction_3<R> d);
	introduces a plane h that passes through point p and that has as an orthogonal direction equal to d.
Plane_3<R> h ( Line_3<R> l, Point_3<R> p);
	introduces a plane h that is defined through the three points l.point(0), l.point(1) and p.
Plane_3<R> h ( Ray_3<R> r, Point_3<R> p);
	introduces a plane h that is defined through the three points r.point(0), r.point(1) and p.
Plane_3<R> h ( Segment_3<R> s, Point_3<R> p);
	introduces a plane h that is defined through the three points s.source(), s.target() and p.

Operations

bool	h.operator== ( h2)
		Test for equality: two planes are equal, iff they have a non empty intersection and the same orientation.
bool	h.operator!= ( h2)
		Test for inequality.
R::RT	h.a ()	returns the first coefficient of h.
R::RT	h.b ()	returns the second coefficient of h.
R::RT	h.c ()	returns the third coefficient of h.
R::RT	h.d ()	returns the fourth coefficient of h.
Line_3<R>	h.perpendicular_line ( Point_3<R> p)
		returns the line that is perpendicular to h and that passes through point p. The line is oriented from the negative to the positive side of h.
Point_3<R>	h.projection ( Point_3<R> p)
		returns the orthogonal projection of $$p on h.
Plane_3<R>	h.opposite ()	returns the plane with opposite orientation.
Point_3<R>	h.point ()	returns an arbitrary point on h.
Vector_3<R>	h.orthogonal_vector ()
		returns a vector that is orthogonal to h and that is directed to the positive side of h.
Direction_3<R>	h.orthogonal_direction ()
		returns the direction that is orthogonal to h and that is directed to the positive side of h.
Vector_3<R>	h.base1 ()	returns a vector orthogonal to orthogonal_vector().
Vector_3<R>	h.base2 ()	returns a vector that is both orthogonal to base1(), and to orthogonal_vector(), and such that the result of orientation( point(), point() + base1(), point()+base2(), point() + orthogonal_vector() ) is positive.

2D Conversion

The following functions provide conversion between a plane and CGAL's two-dimensional space. The transformation is affine, but not necessarily an isometry. This means, the transformation preserves combinatorics, but not distances.

Point_2<R>	h.to_2d ( Point_3<R> p)
		returns the image point of the projection of p under an affine transformation, which maps h onto the $$xy-plane, with the $$z-coordinate removed.
Point_3<R>	h.to_3d ( Point_2<R> p)
		returns a point $$q, such that to_2d( to_3d( p )) is equal to p.
Oriented_side	h.oriented_side ( Point_3<R> p)
		returns either ON_ORIENTED_BOUNDARY, or the constant ON_POSITIVE_SIDE, or the constant ON_NEGATIVE_SIDE, determined by the position of $$p relative to the oriented plane h.

Predicates

For convenience we provide the following boolean functions:

bool	h.has_on ( Point_3<R> p)
bool	h.has_on_positive_side ( Point_3<R> p)
bool	h.has_on_negative_side ( Point_3<R> p)
bool	h.has_on ( Line_3<R> l)
bool	h.is_degenerate ()	Plane h is degenerate, if the coefficients a, b, and c of the plane equation are zero.

Miscellaneous

Plane_3<R>	h.transform ( Aff_transformation_3<R> t)
		returns the plane obtained by applying $$t on a point of h and the orthogonal direction of h.

See Also