G4Ellipse.icc

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// $Id$
//
// --------------------------------------------------------------------
// GEANT 4 inline definitions file
//
// G4Ellipse.icc
//
// Implementation of inline methods of G4Ellipse
// --------------------------------------------------------------------

inline
void G4Ellipse::Init(const G4Axis2Placement3D& position0,
                     G4double semiAxis10, G4double semiAxis20)
{
  position= position0;
  semiAxis1= semiAxis10;
  semiAxis2= semiAxis20;

  ratioAxis2Axis1= semiAxis2/semiAxis1;

  SetBounds(0, 0);

  // needed only for 2D ellipses
  toUnitCircle = G4Scale3D(1/semiAxis1, 1/semiAxis2, 0)
                 * position.GetToPlacementCoordinates();

  forTangent= -semiAxis1*semiAxis1/(semiAxis2*semiAxis2);
}

inline
G4double G4Ellipse::GetSemiAxis1() const
{
  return semiAxis1;
}

inline
G4double G4Ellipse::GetSemiAxis2() const
{
  return semiAxis2;
}


inline
G4double G4Ellipse::GetPMax() const
{
  return CLHEP::twopi;
}

inline
G4Point3D G4Ellipse::GetPoint(G4double param) const
{
  param-= GetPShift();
  return G4Point3D( position.GetLocation()
                    + semiAxis1*std::cos(param)*position.GetPX()
                    + semiAxis2*std::sin(param)*position.GetPY() );
}

inline
G4double G4Ellipse::GetPPoint(const G4Point3D& pt) const
{
  G4Point3D ptLocal= position.GetToPlacementCoordinates()*pt;
  G4double angle= std::atan2(ptLocal.y(), ptLocal.x()*ratioAxis2Axis1);
  G4double r= (angle<0)? angle+CLHEP::twopi: angle;
  return r+GetPShift();
}


#include "G4CurveRayIntersection.hh"

/*
inline
void G4Ellipse::IntersectRay2D(const G4Ray& ray,
                               G4CurveRayIntersection& is)
{
  is.Init(*this, ray);

  // transform s.t. the ellipse becomes the unit circle
  // with the center at the origin

  // 2D operations would be faster
  G4Point3D s= toUnitCircle*ray.GetStart();
  G4Vector3D d= toUnitCircle*ray.GetDir();
  
  // solve (s+i*t)^2 = 1 for i (the distance)

  G4double sd= s*d;
  G4double dd= d.mag2(); // never 0
  G4double ss= s.mag2();

  G4double discr= sd*sd-dd*(ss-1);
  if (discr >= 0) {

    // 2 intersections (maybe 1, but this case is rare)
    G4double sqrtdiscr= std::sqrt(discr);
    // find the smallest positive i
    G4double i= -sd-sqrtdiscr;
    if (i<kCarTolerance) {
      i= -sd+sqrtdiscr;
      if (i<kCarTolerance) {
        return;
      }
    }
    i/= dd;
    G4CurveRayIntersection isTmp(*this, ray);
    isTmp.ResetDistance(i);
    is.Update(isTmp);

  }
}
*/

inline
G4int G4Ellipse::IntersectRay2D(const G4Ray& ray)
{
  // transform s.t. the ellipse becomes the unit circle
  // with the center at the origin

  // 2D operations would be faster
  G4Point3D  st= toUnitCircle*ray.GetStart();
  G4Vector3D d= toUnitCircle*ray.GetDir();
  
  // solve (st+i*t)^2 = 1 for i (the distance)
  G4double sd= st*d;
  G4double dd= d.mag2(); // never 0
  G4double ss= st.mag2();

  G4double discr= sd*sd-dd*(ss-1);
  G4int nbinter = 0;
  G4double i;

  if (discr > 0) 
  {
    // 2 intersections 
    G4double sqrtdiscr= std::sqrt(discr);
   
    // if i is positive, we have an intersection
    i= -sd-sqrtdiscr;
    if (i > kCarTolerance) 
      nbinter++;
      
    i= -sd+sqrtdiscr;
    if (i > kCarTolerance) 
      nbinter++;      
  }
  
  // if the ray is tangent on the circle
  if (discr == 0)
    nbinter = 1;

  return nbinter;
}

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