SlastShowerGenerator

 This is ctor

 SlastShowerGenerator is initialized reading from config/LightToEuso/GeneratorLightToEuso.cfg file
 Edit that file to setup desired parameters of the showers such as energy, theta, phi intervals
 or initial position in case of unique parameters.
 Init() is called in SlastShowerGenerator ctor

  This is dtor

 This is a special method to setup desired showertrack parameters from the code (not from the config file)
 This can be a usefull function in the reconstruction code

 Returns atmosphere depth before the first interaction.
 Attention: units are ESAF internal. In order to get in human way one has to multiple by cm2/g

 SlastShowerGenerator internal function which computes the hadronic interactio  length.
 Used by GetX1() method

Computes NUCLEN + AIR CROSS SECTION:
... USES AN EMPIRICAL PARAMETRIZATION OF TOTAL INELASTIC
... NUCLEON AIR CROSS SECTION (in mbarn)
... INPUT:  NUCLEON ENERGY in eV
... OUTPUT: NUCLEON AIR CROSS SECTION (in mbarn)
... REFERENCES:
... 1. Mielke H.H., Foller, M, Knapp J.
...    // J.Phys.G: Nucl.Part.Phys. 1994. V 20, P637
... 2. V.A. Naumov, T.S. Sinegovskaya (eq (17))

 Filling the ShowerStep object with relevant information

 Assigning of fNe - number of electrons in the current step according to the Shower Parameterization.
  GIL stands for Greizen-Ilina-Linsley which is the QGSJET model
 parameterization.
 GFA stands for Gaussian Function in Age
 GHF stands for Gaisser Hillas Function

 Generates point uniformly on top of atmosphere on the upper part of the earth hemisphere
 theta, phi angles are taken at TOA impact, then translated into MES frame for further steps of event simulation

 returns true if pos is within Euso FoV cone

 finds the intersection between the given track and the Euso FoV cone, if exists
 if does not exist, returns (0,0,HUGE)

 intersection considered only above ground

 X1 is known --> find the first point fInitPoint from TOA impact
 if event goes out atmosphere / OR / reaches ground without interacting, returns kFALSE

 Assess Xmax position and tell if it is in FoV
 used to reject event with Xmax out of FoV, without simulating the dvpt

 This method checks if next point is visible and makes the next step if it is OK.

 Assigning of fNe - number of electrons in the current step according to GIL parameterization.
 (GIL stands for Greizen-Ilina-Linsley which is the QGSJET model parameterization.

 Assigning of fNe - number of electrons in the current step according to Gaussian Function in Age parameterization.
 Formulae from C. Song, Astropart. Physics 22(2004)151
 sigma values fitted and extrapolated, Xmax, Nmax from GHF used
 Factor 1.1 added to Ne because of threshold energy used for corsika simulation (10% particles missing)

 WARNING !!!     not usable yet, cause cannot currently handle X1 fluctuations

 Assigning of fNe - number of electrons in the current step according to
 Gaisser Hillas    parametrisation
 Formulae from C. Song, Astropart. Physics 22(2004)151
 Xmax, Nmax, lambda, X1, X0 values fitted and extrapolated
 Factor 1.1 added to Ne because of threshold energy used for corsika simulation (10% particles missing)

 WARNING !!!     not usable yet, cause cannot currently handle X1 fluctuations

 method returning the ShowerTrack object

 Reset ShowerTrack and SlastShowerGenerator internal parameters

 Fills ShowerTrack parameters

 Method developing the shower

 Method returning the Truth object

 returns Xmax of the shower according to GIL parametrization (used by Reco)