gpiv_errvec (1)

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 harm.

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 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.

gpivtools

Gerber Van der Graaf

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