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       gpiv_peaklck  -  Tests PIV data on the so-called peak-locking effect by
       printing/displaying an histogram of the particle displacements at  sub-
       pixel level.


       gpiv_peaklck  [-g] [-h | --help] [-n N] [-p | --print] [-v | --version]
       [filename] < stdin > stdout


       Peak-locking effects in Particle Image Velocimetry  (PIV)  result  into
       estimations of the particle displacements that are mainly at an integer
       number of pixels, instead of at sub-pixel  displacements.  This  effect
       may  due  to  stretching  of the (round) pixel images, due to a too low
       resolution of the pixel-image or may be due to signal interferences  of
       the  data  from  camera  to frame grabber.  Gpiv_Peaklck calculates the
       particle displacement distribution at sub-pixel level in between 0.0 an
       1.0  (0  included,  1  excluded). If peak locking occurs, a non-uniform
       distribution of the estimated particle displacements at sub-pixel level
       will be found.

       The   configuration  parameters  (containing  the  VALID  key)  may  be
       overruled by the command line options, as explained below.


       -g     Graphical visualization of the histogram with gnuplot.

       -h | --help
              On-line help

       -n N   Override number of bins (default 10, hard coded).

       -p | --print
              Print parameters, command line options and eventually used input
              and  output  filenames  to  stdout.   The  output  is identic of
              filename.par, in case -f is used.

       -v | --version
              Print  version  information  on  standard  output,   then   exit

              Input  PIV data file. Overrides stdin and stdout. Output will be
              written to filename.plk.  The  parameters  will  be  written  or
              appended  to  filename.par  and  may  be  used for future use by
              including them in ./gpivrc.




       Gerber Van der Graaf


       The program seems to work fine with real PIV data.  So far, no  serious
       bugs have been found.

                                8 November 2006