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)