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     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

     This simulation is based on OpNovice and OpNovice2

Build requirements
  Geant4 compiled with GDML and additional datasets
  ROOT
  -CADMesh is required to read CAD models (i.e. stl, step), but is optional for compiling


main()
------

 ==> define Random Number Engine, initial seed, CAD input and GDML output

G4VUserPhysicsList
------------------

 ==> define particles; including *** G4OpticalPhoton     ***
     define processes; including *** G4Cerenkov          ***
                                 *** G4Scintillation     ***
                                 *** G4OpAbsorption      ***
                                 *** G4OpRayleigh        ***
                                 *** G4OpBoundaryProcess ***

Materials
---------

==> defines many materials for potential use
    For our purposes the G4OpticalSurface AlSurface and the G4Material Al and Air
    will be given optical properties and used for construction.


G4VUserDetectorConstruction
---------------------------

 ==> A light guide is made either by simple G4trd or by importing a model
     via CADMesh.
     define G4LogicalBorderSurface between the light guide and world volume
     defines a PMT window sensitive detector at the top of the light guide
     AlSurface properties can be modified via DetectorMessenger via the following commands
     /lightGuide/surfaceModel
     /lightGuide/surfaceType
     /lightGuide/surfaceFinish
     /lightGuide/surfaceSigmaAlpha
     /lightGuide/surfaceProperty

     examples can be found in run1.mac


G4VUserPrimaryGeneratorAction
-----------------------------

 ==> Use G4GeneralParticleSource to shoot an optical photon into the light guide
     Particle type and distribution is set in run1.mac


G4UserRunAction
---------------

==> define G4Timer (start/stop)
    define G4AnalysisManager (output .root file)
    set verbose levels


PMTHit
------

==> stores G4int         trackID,
           G4ThreeVector pos;      // Origin position of the photon
           G4ThreeVector hit;      // Location where the photon hit the PMT window
           G4double      energy;   // Energy of the photon
           G4ThreeVector momentum; // Momentum of the photon (direction)
           G4double      time;     // Time of arrival of the photon
    for each hit on the PMT sensitive detector


PMTSD
------

==> Records a PMTHit if the photon strikes the PMT window

G4UserEventAction
---------------

==> Adds data from a PMTHit to the output root file

Visualisation
-------------

 The Visualization Manager is set in the main().
 The initialisation of the drawing is done via a set of /vis/ commands
 in the macro vis.mac. This macro is automatically read from
 the main in case of interactive running mode.

 HOW TO START
 ------------

 - compile and link to generate an executable
  % mkdir zdclg-build zdclg-install
 	% cd zdclg-build
 	% cmake -DCMAKE_INSTALL_PREFIX=../zdclg-install /path/to/zdclg

   This example handles the program arguments in a new way.
   It can be run with the following optional arguments:
   % ./lightGuide [-m macro ]
                  [-u UIsession]
                  [-t nThreads]
                  [-r seed]
                  [-o outputFileName]
                  [-c CADmodelName filetype]
                  [-co GDMLoutFileName]

   The -t option is available only in multi-threading mode
   and it allows the user to override the Geant4 default number of
   threads. The number of threads can be also set via G4FORCENUMBEROFTHREADS
   environment variable which has the top priority.

 - execute lightGuide in 'batch' mode from macro files
 	% ./lightGuide -m run1.mac

 - execute lightGuide in 'interactive mode' with visualization
 	% ./lightGuide
 	....
 	Idle> type your commands. For instance:
 	Idle> /control/execute run1.mac
 	....
 	Idle> exit