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       gpiv_errvec  -  Searches  erroneous  vectors  in  a  PIV  data file and
       substitutes with new values.


       gpiv_errvec [-a] [-b ] [-g][-h] [-h | --help] [-i | --image_type S] [-n
       N]  [--no_b ] [-p | --print] [-r N] [-s N] [-t F] [-u | --surround] [-v
       | --version] [filename] < stdin > stdout


       gpiv_errvec searches erroneous  outliers  in  a  PIV  data  stream  and
       substitutes with new values, if possible, i.e. if (the majority) of its
       surroundings are non-erroneous.  Evaluation  of  erroneous  vectors  is
       done  by  looking  up  the Signal to Noise Ratio (SNR) value in the PIV
       data file or by calculating the median residu of the  vector  with  its
       surroundings.  A  new displacement is obtained by the mean value of the
       surrounding values or by the location of the next higher  peak  in  the
       covariance function.

       PIV data validation is not needed anymore while this is now done during
       image interrogation with gpiv_rr. Though  using  gpiv_errvec  will  not

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


       -a     Automatic threshold;  calculates  threshold  value  from  residu

       -b     Calculate   statistics  of  the  median  residues  and  print  a
              histogram of N bins.

       -g     Graphical visualization of residu statistics with gnuplot (needs
              filename).  -b  is  not  required  as  this  option  will be set

       -h | --help
              On-line help.

       -i | --image_type S
              Image type or format to be used if particle  displacements  will
              have  to be re-estimated at the next highest correlation peak. S
              may be png, tif, gif, bmp, pgm, r or gpi. Default: png.

       -n N   Defines number of histogram of bins N for -b or -a

       --no_b N
              suppresses printing median residu histogram

       -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 filename is used.

       -r N   Erroneous vector determined by SNR of the  correlation  function
              (N  =  0),  median  residu (N = 1) or normalized median (N = 2),
              i.e. the ratio between  median  residu  with  current  datapoint
              included   and   between  median  residu  of  surroundigs  (with
              datapoint excluded).

       -s N   Substitution of the erroneous vectors by (N =  0)  nothing,  the
              local  mean  from the surrounding values (N = 1), median (N = 2)
              or next highest covariance peak (N = 3, needs filename).

       -t F   Threshold value F of SNR or median residu to determine  validity
              of particle displacement.

       -u | --surround
              Odd  number  representing the surrounding grid points to be used
              for local mean and median values.

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

              Full  name  of  PIV  data  file for input. Substitutes stdin and
              stdout.  Output  will  be  written  to   filename.erv.piv.   The
              parameters  will  be written or appended to filename.par and may
              be used for  future  use  by  including  them  in  ./gpivrc.  If
              particle  displacements will have to be re-estimated at the next
              highest correlation peak, filename is required.




       Gerber Van der Graaf


       The program has been tested for artificial generated  DPIV  images.  So
       far, no serious bugs have been found.

                                  23 May 2005