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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_typeS] [-nN] [--no_b] [-p|-rN] [-sN] [-tF] [-u|--surround] [-v|--version] [filename] <stdin>stdout

gpiv_errvecsearches 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 withgpiv_rr. Though usinggpiv_errvecwill not harm. The configuration parameters (containing theVALIDkey) may be overruled by the command line options, as explained below.

-aAutomatic threshold; calculates threshold value from residu histogram.-bCalculate statistics of the median residues and print a histogram ofNbins.-gGraphical visualization of residu statistics with gnuplot (needsfilename).-bis not required as this option will be set automatically.-h|--helpOn-line help.-i|--image_typeSImage type or format to be used if particle displacements will have to be re-estimated at the next highest correlation peak.Smay be png, tif, gif, bmp, pgm, r or gpi. Default: png.-nNDefines number of histogram of binsNfor-bor-a--no_bNsuppresses printing median residu histogram-p|filename.par, in casefilenameis used.-rNErroneous 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).-sNSubstitution 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, needsfilename).-tFThreshold valueFof SNR or median residu to determine validity of particle displacement.-u|--surroundOdd number representing the surrounding grid points to be used for local mean and median values.-v|--versionPrint version information on standard output, then exit successfully.filenameFull name of PIV data file for input. Substitutes stdin and stdout. Output will be written tofilename.erv.piv. The parameters will be written or appended tofilename.parand 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,filenameis required.

gpivtools

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