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
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
-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
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
-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