class THaOptics::TOpticsPos: public THaOptics::TOpticsDir

    THaOptics

  Read in track X,Y,Theta,Phi in TRCS and fill in any thing else in THaTrack



 Author: Jin Huang <mailto:jinhuang@jlab.org>    Jan 2008
    Modify History:
      Mar 2007    Jin Huang <mailto:jinhuang@jlab.org>
          Modify ApplyOptics to give a central trajectory





THIS IS an abstract class basis for general optics class.
It has following functions:
> handles general optics interface
> managing beam information
> supporting coordinate transformation (see child class TOpticsDir and TOpticsPos).
> supporting some geometry calculation such as CrossingSurfLine3D(...)



TERMINOLOGY used in this class follows conventions of Hall A
Tech Notes JLAB-TN-02-012:
http://hallaweb.jlab.org/publications/Technotes/files/2002/02-012.pdf



DERIVED CLASS should reload function of virtual Int_t ApplyOptics(...).



FOUR DERIVED OPTICS CLASS have been implemented, each with difference algorithm,
but using same interface defined by this class. They are THaOpticsAnalytical,
THaOpticsHRS, THaOpticsNoFeild and THaOpticsAGen.



USAGE: to make a spectrometer support this series of optics classes,
following code have to be included:

0.#include "THaOptics.h"

1.in class definition:
public:
virtual Bool_t   MountOptics(THaOptics *);
protected:
TRef            fOptics;  //pointer to optics calculation class
public:
inline THaOptics *  GetOptics() const
{return (THaOptics *)(fOptics.GetObject());}

2.in destructor:
if (fOptics.IsValid()) delete (THaOptics *)(fOptics.GetObject());

3.anywhere in spectrometer.cxx:
Bool_t THaBigBite::MountOptics(THaOptics *Optics)
{
mount a optics class to the Spectrometer.
return true if successful.
Notice: This function have to be called
before Init() to make sure readdatebase
        is called for the optics class.

if (fOptics.IsValid()) {
DEBUG_WARNING("MountOptics",
"The Optics has already been mounted. Deleting the old one and mounting new.");
delete fOptics.GetObject();
}

fOptics=Optics;

return fOptics.IsValid();
}

4.reload THaSpectrometer::FindVertices(TClonesArray& tracks ) and add:
if (fOptics.IsValid())
{
Int_t n_exist = tracks.GetLast()+1;

for( Int_t t = 0; t < n_exist; t++ ) {
THaTrack* theTrack = static_cast<THaTrack*>( tracks.At(t) );
assert(fOptics.IsValid());
((THaOptics *)(fOptics.GetObject()))-> ApplyOptics (theTrack);
}
}

5.reload THaSpectrometer::Init( const TDatime& run_time ) and add:
THaAnalysisObject::EStatus stat=THaSpectrometer::Init(run_time);
if (stat!=kOK) return stat;

Optics is the last one to be initialized.
So it could use any other variable
if (fOptics.IsValid())
stat=((THaOptics *)(fOptics.GetObject()))->Init(run_time);

6.(optional)in constructor:
Bool_t mr=MountOptics(new <the optics class name>(<name>,<description>,this));

7.(optional)in the code, one can always reassign a difference optics
class to the spectrometer by calling MountOptics(THaOptics *);




Child Class THaOptics::TOpticsDir

a vector class with information of it's Coordinate System
also handles Coordinate transformation. But it only handle
rotation of the vector. It's useful to describe a direction
For example, p vector




Child Class THaOptics::TOpticsPos

a vector class derived from THaOptics::TOpticsDir, specially designed
for position coordinate, ex vertex.