G4LineSection.cc

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//
// G4LineSection implementation
//
// Created: J.Apostolakis, 1999
// --------------------------------------------------------------------

#include "G4LineSection.hh" 

G4LineSection::G4LineSection( const G4ThreeVector& PntA, 
                              const G4ThreeVector& PntB )
  : EndpointA(PntA), VecAtoB(PntB-PntA)
{ 
  fABdistanceSq = VecAtoB.mag2();  
}

G4double G4LineSection::Dist( G4ThreeVector OtherPnt ) const
{
  G4double       dist_sq;  
  G4ThreeVector  VecAZ;
  G4double sq_VecAZ, inner_prod, unit_projection ; 

  VecAZ= OtherPnt - EndpointA;
  sq_VecAZ = VecAZ.mag2();

  inner_prod= VecAtoB.dot( VecAZ );
   
  //  Determine  Projection(AZ on AB) / Length(AB) 
  //
  if( fABdistanceSq != 0.0 )
  {
    //  unit_projection= inner_prod * InvsqDistAB();
    unit_projection = inner_prod/fABdistanceSq;

    if( (0. <= unit_projection ) && (unit_projection <= 1.0 ) )
    {
      dist_sq= sq_VecAZ -  unit_projection * inner_prod ;
    }
    else
    {
     //  The perpendicular from the point to the line AB meets the line
     //   in a point outside the line segment!
     
      if( unit_projection < 0. ) // A is the closest point
      {
        dist_sq= sq_VecAZ;  
      }
      else                       // B is the closest point
      {
        G4ThreeVector   EndpointB = EndpointA + VecAtoB;
        G4ThreeVector   VecBZ =     OtherPnt - EndpointB;
        dist_sq =  VecBZ.mag2();
      }
    }
  }
  else
  {
     dist_sq = (OtherPnt - EndpointA).mag2() ;   
  }  
  if( dist_sq < 0.0 ) dist_sq = 0.0 ;

  return std::sqrt(dist_sq) ;  
}