NAME

       funcen - find centroid (for binary tables)

SYNOPSIS

       funcen [\-i] [\-n iter] [\-t tol] [\-v lev] <iname> <region>

OPTIONS

         -i            # use image filtering (default: event filtering)
         -n iter       # max number of iterations (default: 0)
         -t tol        # pixel tolerance distance (default: 1.0)
         -v [0,1,2,3]  # output verbosity level (default: 0)

DESCRIPTION

       funcen  iteratively calculates the centroid position within one or more regions of a Funtools table (FITS
       binary table or raw event file).  Starting with an input table, an initial region specification,  and  an
       iteration count, the program calculates the average x and y position within the region and then uses this
       new position as the region center for the next iteration. Iteration terminates when the maximum number of
       iterations  is  reached or when the input tolerance distance is met for that region. A count of events in
       the final region is then output,  along  with  the  pixel  position  value  (and,  where  available,  WCS
       position).

       The  first  argument to the program specifies the Funtools table file to process.  Since the file must be
       read repeatedly, a value of "stdin" is not permitted when the number of  iterations  is  non\-zero.   Use
       Funtools Bracket Notation to specify FITS extensions and filters.

       The  second  required argument is the initial region descriptor. Multiple regions are permitted. However,
       compound regions (accelerators, variable argument regions and regions connected via boolean algebra)  are
       not  permitted.  Points  and  polygons  also  are illegal. These restrictions might be lifted in a future
       version, if warranted.

       The \-n (iteration number) switch specifies the maximum number of iterations to perform. The  default  is
       0,  which  means  that  the  program  will  simply  count and display the number of events in the initial
       region(s).  Note that when iterations is 0, the data can be input via stdin.

       The \-t (tolerance) switch specifies a floating point  tolerance  value.  If  the  distance  between  the
       current  centroid  position  value  and  the  last  position  values  is  less than this value, iteration
       terminates.  The default value is 1 pixel.

       The \-v (verbosity) switch specifies the verbosity level of the output. The default is 0,  which  results
       in a single line of output for each input region consisting of the following values:

         counts x y [ra dec coordsys]

       The  last  3  WCS  values  are  output if WCS information is available in the data file header. Thus, for
       example:

         [sh] funcen -n 0 snr.ev "cir 505 508 5"
         915 505.00 508.00 345.284038 58.870920 j2000

         [sh] funcen -n 3 snr.ev "cir 505 508 5"
         1120 504.43 509.65 345.286480 58.874587 j2000

       The first example simply counts the number of events in the initial region.  The second example  iterates
       the centroid calculation three times to determine a final "best" position.

       Higher  levels  of  verbosity  obviously  imply  more  verbose output. At level 1, the output essentially
       contains the same information as level 0, but with keyword formatting:

         [sh] funcen -v 1 -n 3 snr.ev "cir 505 508 5"
         event_file:     snr.ev
         initial_region: cir 505 508 5
         tolerance:      1.0000
         iterations:     1

         events:         1120
         x,y(physical):  504.43 509.65
         ra,dec(j2000):  345.286480 58.874587
         final_region1:  cir 504.43 509.65 5

       Level 2 outputs results from intermediate calculations as well.

       Ordinarily, region filtering is performed using analytic (event)  filtering,  i.e.  that  same  style  of
       filtering  as  is  performed by fundisp and funtable. Use the \-i switch to specify image filtering, i.e.
       the same style filtering as is performed by funcnts.  Thus, you can perform a quick calculation of counts
       in regions, using either the analytic or image filtering method, by specifying the
        \-n 0 and optional \-i switches. These two method often give different results because of  how  boundary
       events are processed:

         [sh] funcen  snr.ev "cir 505 508 5"
         915 505.00 508.00 345.284038 58.870920 j2000

         [sh] funcen -i snr.ev "cir 505 508 5"
         798 505.00 508.00 345.284038 58.870920 j2000

       See Region Boundaries for more information about how boundaries are calculated using these two methods.

SEE ALSO

       See funtools(7) for a list of Funtools help pages

version 1.4.2                                    January 2, 2008                                       funcen(1)