NAME

    gtvcut - This tool displays a summary of the Data Sub-Space keywords. 


USAGE
    
    gtvcut infile table


DESCRIPTION

    gtvcut is used to view the Data Sub-Space (DSS) keywords in a given
    extension, where the EVENTS extension is assumed by default. The DSS
    keywords scheme was introduced for recording data selection criteria
    in a systematic manner. Note that inspection of the file extension 
    with the tools fv or ds9 would serve the same purpose.

    For FERMI data, DSS keywords store information in the FITS headers
    about the selection criteria that have been applied to the data using
    the gtselect tool (type "fhelp gtselect" for further explanation). The 
    DSS keywords are used by the exposure-related tools (gtexpmap, gtrspgen)
    and by gtlike for calculating various quantities, such as the
    predicted number of detected events given the source model. These
    keywords must be exactly the same for all of the filtered event files
    considered in a given analysis. gtlike will check to ensure that all
    of the DSS keywords are the same in all of the relevant files.

    A filtering condition is expressed with a set of keywords (e.g., DSTYP1,
    DSUNI1, DSVAL1, and DSREF1). For example, selecting events in a given 
    time interval (TIME>start_time&&TIME<end_time), the filtering conditions 
    are stored as

    DSTYP3: TIME
    DSUNI3: s
    DSVAL3: TABLE
    DSREF3: :GTI

    or

    DSTYP3 = TIME
    DSUNI3 = s   
    DSVAL3 = start_time:end_time

    Selecting events in a given energy range 
    (ENERGY>start_energy&&ENERGY<end_energy), the filtering conditions are
    stored as

    DSTYP4: ENERGY
    DSUNI4: MeV
    DSVAL4: start_energy:end_energy


PARAMETERS

    infile [filename]
         Input event FITS file. This is the file containing the LAT event data.
	
    table [string]
         Data extension name. Default (and only possible) is "EVENTS".
 	 	 
    (suppress_gtis) [boolean]
         Flag to suppress the printing of the individual GTI start and stop
         times. Default is "no".
 	 	 
    (chatter) [integer]  
         This parameter fixes the output verbosity: no screen output (0),
         nominal screen output (2), maximum verbosity (4). Default is "2".

    (clobber) [boolean]
         If true, an existing file of the same name will be overwritten. 
         Default is "yes".
    
    (debug) [boolean]
         Activate debugging mode. Default is "no". When debug is "no", all 
         exceptions that are not caught and
         handled by individual tool-specific code are caught by a top-level
         exception handler that displays information about the exception and
         then exits. When debug is "yes", such exceptions are not caught by the
         top level code. Instead the tool produces a segmentation violation,
         which is more useful for debugging. When debugging mode is enabled,
         the tool produces more verbose output describing any errors or
         exceptions that are encountered.
    
    (gui) [boolean]
         Graphical User Interface (GUI) mode is activated if set to "yes".
         Default is "no".
    
    (mode) [string]
         Mode of automatic parameters: "h" for batch, "ql" for interactive. 
         Default is "ql".


EXAMPLES

    Parameters are passed following the FTOOLs model. They could be passed
    answering from a prompt, as a list in a command line, or by editing
    the parameter file.
 
    To be prompted for gtvcut simply type in the command line: 

> gtvcut

    This will prompt for parameter values. Not all parameter are prompted: 
    some of them are "hidden". To change one of the "hidden" parameter, 
    the user should specify the values in the command line or modify its 
    mode by editing the parameter file. 
    For example, to suppress the printing of the individual GTI start and 
    stop times, the following command line as to be typed:

> gtvcut suppress_gtis=yes

    In the next example the gtselect tool (see the gtselect help) was applied
    first selecting a time range of the events in the original event file
    between 252374400 (MET sec) and 252460800 (MET sec), an energy
    range between 30 MeV and 200000 MeV, and a region of 20 degrees
    from a central point at coordinates RA=193.98 DEC=-5.82.

> gtvcut
Input FITS file[] events.fits
Extension name[EVENTS]

    The output is as follows:
    
DSTYP1: BIT_MASK(EVENT_CLASS,0,P7REP)
DSUNI1: DIMENSIONLESS
DSVAL1: 1:1

DSTYP2: POS(RA,DEC)
DSUNI2: deg
DSVAL2: CIRCLE(193.98,-5.82,20)

DSTYP3: TIME
DSUNI3: s
DSVAL3: TABLE
DSREF3: :GTI

GTIs:
252374400 252460800

DSTYP4: ENERGY
DSUNI4: MeV
DSVAL4: 30:200000

DSTYP5: ZENITH_ANGLE
DSUNI5: deg
DSVAL5: 0:105


    That last example could be also be run in the command line as follows:

> gtvcut infile=events.fits table=EVENTS


KNOWN BUGS


SEE ALSO

     gtselect
