NAME

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

SYNOPSIS

       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

DESCRIPTION

       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 harm.

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

Options

       -a     Automatic threshold; calculates threshold value from residu histogram.

       -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 automatically.

       -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 successfully.

       filename
              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.

SEE ALSO

       gpivtools

AUTHOR

       Gerber Van der Graaf

BUGS

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

                                           23 May 2005                             GPIV_ERRVEC(1)