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\section{Camera Program}

\subsection{Abstract}
	
The Camera Program is for the simulation of the MAGIC camera. The
input is the output of the program Reflector, what are all the
cerenkov photons hitting the camera. All these photons are reflected
from the mirrors. 

The determination of the pixel that is hitted by one cerenkov photon
is the first working step of the program. Then the simulation of the
different efficencies inside the camera are following (i.e. the
absorption due to the distance between mirrors and the camera plane, 
the quantuum efficency of the photocathod...). 
So after this first part we
know the time and the Pixel identification of each
photo electron leaving the photo cathod. 

The simulation of the trigger is the next step inside the camera
program.  
For each photo electron one create a standard response signal.
Also the noise (from opto-electonic) of the trigger signal is
implemented. 
After doing this for all photo electrons, the program
calculates the diskriminator signal for each channel. With this
digital signals the program decides  if a trigger is created. 
All this trigger studies are implemented in
the (C++) class MTrigger. At the end of each event you have the
knowledge if there occurs a trigger signal or not. 

The output of the program is a root tree (using the root package from
CERN). In this tree there are different branches. One branch stores
the information about the MonteCarlo event (McEvt). One the result of
the trigger studies (McTrig). And last but not least, there is a
branch in which the expected raw data format is stored (MRawEvt). 
 
\subsection{Usage}

To start the Camera Program you have to create a steercard file (see
chapter \ref{chap_steercard}).
I.e. this file is called {\bf input.card}. Then start the program with
the command:
\begin{center}
 \bf {camera $<$ input.card }
\end{center}
With the steercard file one can control the program and its different
features. In the followin you will find a special list of all the 
steercard control words. 

\subsection{Steercard control}
\label{chap_steercard}

With the steercard file the user can control the procedure of the
Camera Program. At the beginning of the program, all lines in this
file are read in. Depending on the first word in the line, a control
value for the further program behaviour is set. 

A list of the different steerword is following. They are seperated by
their importance for a good simulation. 

\begin{itemize} 
  \item {\bf input and output files} \\
	 the following steerword are neccessary to read in the data
	 from the right file and to store the output in the right
	 files. 

	\begin{itemize}
	   \item {\bf ct\_file } \\
		This steerword controls the geometry of the used
   	 	cerenkov telescope. At the beginning of the
   	        development is was planned to simulated different
	        types (MAGIC and CT1 of HEGRA). But if you want to
        	simulated only for MAGIC put the following line into
		your steercard file: \\
		ct\_file   \hspace{10mm}   ../Data/magic.def
	   \item {\bf input\_file} \\
		With this line you declare the input file for the
		camera program. The input file is the output file of
		the Reflector Program. So the line may look like: \\
		input\_file  \hspace{10mm}     /dat1/RefData/prot.rfl
	   \item {\bf root\_file} \\
		The output of the Camera Program is written in a root
		tree. To give the root file a name used this steercard
		control line: \\
		root\_file   \hspace{10mm}     /dat1/CamData/prot.root

		To control the different branches of the root tree,
	   	there are some steerwords to do this job. 
                \begin{itemize}
		   \item {\bf nowrite\_McEvt} \\
			In a normal run the Camera Program writes
	   		the information of the Monte Carlo Event to
	   		the root tree. If you use a line like:
			nowrite\_McEvt \\
			it does not. This is useful for testing the 
			reconstruction precision, because the analyser 
			doesn't now anaything about the input. 
			
                   \item {\bf write\_RawEvt} \\
			If you want to create the branch with the raw 
			data format of the events, you must use this
			command. If you don't use it, the camera
			program will not create and fill this branch. 
			
		   \item {\bf write\_McTrig} \\
			To study some properties of the triggers, it
			is useful to create a branch with the McTrig
			information in it. To do this use this
			steerword. If you don't use it, you won't get
			any McTrig information.   

                   \item Be aware! If you don't use one of this three 
			steerwords, you get only the Monte Carlo
			Information (McEvt) in your root tree file. 
		\end{itemize}
	\end{itemize}

   \item {\bf amount of output data} \\
	For different studies on needs a different amount of output
	data. To study trigger effiencies it is neccessary to write
	all events to file, but for the optimisation of reconstruction
	methods you need only the triggered events. There is a
	steerword, that controls the difference: 
	\begin{itemize}
	   \item {\bf write\_all\_images} \\
		If you use this steerword, you write out all events. 
		But the default behaviour is to write only the
		triggered events. 

	\end{itemize}
   \item {\bf Parameters of the camera} \\
	It is possible to control some behaviours of the camera with
	the steercard. They all are listed here: 
	\begin{itemize}
	   \item {\bf ana\_pixels} \\
		In earlier development steps it was possible to change
	   	the size of the camera with this variable. But for the
		actual version of the camera layout it is neccessary
	   	to put the following line into your steercard: 
  		ana\_pixels   \hspace{10mm}     577
	   \end{itemize}

   \item {\bf Simulation of the Night Sky Background} \\
	Due to the night sky background there are a lot of other
	photons reaching the camera. It is possible to simulate the
	behaviour of such NSK photons using the Camera Program. 
	You can switch the NSB on and set the value of NSB photons. 
	This is done with the following steerwords: 
	\begin{itemize}
	   \item {\bf nsb\_on} \\
		To start the simulation of the NSB use this
		steerword.
	   \item {\bf nsb\_mean} \\
		To set the NSB to a given value use the following
		line:\\[1mm]
		nsb\_mean   \hspace{10mm}     0.09 \\[1mm]
		This value corresponds to 0.09 NSB photon in 1 ns for
		the inner pixels. 
	\end{itemize}
	

   \item {\bf Parameters of the random generator} \\
	The simulation of some efficencies need a random
	generator. This generator is a part of the ranlib. To set the
	seed of the generator you can use the following steercard
	line: 
	\begin{itemize}
	   \item {\bf seeds} \\
		You must put a line in your steercard file, that looks
		like: 	 \\ 
  		seeds   \hspace{5mm}  12345\hspace{5mm}  67890
	   \end{itemize}

   \item {\bf Don't forget the end} \\
	Very important is the last line in the steercard file. This
	linie indicates the end of the steercard. So don't forget to
	put end\_file marker at the end of the file!!\\[1mm]
	{\bf end\_file} \\
\end{itemize}
So at the end the file may look like: 
\begin{verbatim}
#
input_file    /dat1/RefData/gamma.rfl
root_file     /dat1/CamData/gamma.root
#
ct_file       ../Data/magic.def
#
write_all_images
#
write_McTrig
#
ana_pixels    577
#
seeds   69184 10406
#
end_file
\end{verbatim}

\end{document}




