Class describing a geometrical plane in 3 dimensions.
      A Plane3D is a 2 dimensional surface spanned by two linearly independent vectors.
      The plane is described by the equation
      \f$ a*x + b*y + c*z + d = 0 \f$ where (a,b,c) are the components of the
      normal vector to the plane \f$ n = (a,b,c)  \f$ and \f$ d = - n \dot x \f$, where x is any point
      belonging to plane.
      More information on the mathematics describing a plane in 3D is available on
      <A HREF=http://mathworld.wolfram.com/Plane.html>MathWord</A>.
      The Plane3D class contains the 4 scalar values in double which represent the
      four coefficients, fA, fB, fC, fD. fA, fB, fC are the normal components normalized to 1,
      i.e. fA**2 + fB**2 + fC**2 = 1
      @ingroup GenVector
| void | Normalize() | 

         generic constructors from the four scalar values describing the plane
	 according to the equation ax + by + cz + d = 0
         \param a scalar value
         \param b scalar value
         \param c scalar value
         \param d sxcalar value
         Construct from a generic DisplacementVector3D (normal vector) and PositionVector3D (point coplanar to
         the plane)
	 \param n normal expressed as a generic ROOT::Math::DisplacementVector3D
	 \param p point  expressed as a generic ROOT::Math::PositionVector3D
{}
         constructor from three generic point belonging to the plane
	 \param p1 point1 expressed as  ROOT::Math::DisplacementVector3D<Cartesian3D<double> >
	 \param p2 point2 expressed as  ROOT::Math::DisplacementVector3D<Cartesian3D<double> >
	 \param p3 point3 expressed as  ROOT::Math::DisplacementVector3D<Cartesian3D<double> >
{} compiler-generated copy ctor and dtor are fine.
 ------ assignment ------
         Assignment operator from other Plane3D class
         Return the a coefficient of the plane equation \f$ a*x + b*y + c*z + d = 0 \f$. It is also the
         x-component of the vector perpendicular to the plane.
{ return fA; }
         Return the b coefficient of the plane equation \f$ a*x + b*y + c*z + d = 0 \f$. It is also the
         y-component of the vector perpendicular to the plane
{ return fB; }
         Return the c coefficient of the plane equation \f$ a*x + b*y + c*z + d = 0 \f$. It is also the
         z-component of the vector perpendicular to the plane
{ return fC; }Return the Hesse Distance (distance from the origin) of the plane or the d coefficient expressed in normalize form
Return the signed distance to a Point. The distance is signed positive if the Point is in the same side of the normal vector to the plane. \param p Point expressed in Cartesian Coordinates
Return the projection of a Cartesian point to a plane \param p Point expressed as PositionVector3D<Cartesian3D<double> >
 ------------------- Equality -----------------
         Exact equality