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Helix.h

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// $Header: /nfs/slac/g/glast/ground/cvs/geometry/geometry/Helix.h,v 1.2 2000/01/18 00:42:06 burnett Exp $
//
#ifndef GEOMETRY_HELIX_H
#define GEOMETRY_HELIX_H

#include "geometry/Ray.h"

class Helix : public Ray
{
 public:
   Helix( const Point& p, const Vector& d, const Vector& a,
                         double r );
   Helix( const Helix& h );


   Point position( double step ) const;
   Vector direction( double step ) const;

   double curvature(double =0) const{ return rho? 1.0/rho : FLT_MAX; }


   double step() const { return rho? 2.* fabs(rho) : FLT_MAX; }

   GeomObject& transform( const CoordTransform &);

   const char *nameOf() const { return "Helix"; }
   void printOn( std::ostream& os = std::cout ) const;

 private:
   Vector axis;         // helix axis direction (unit vector)
   double rho;          // helix radius, sign significant
   Vector perp;         // perpendicular direction
   double parallel;     // component along axis (for efficiency)
   void updateCache(double)const;
};

#endif

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