## 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.

## AUTHOR

Gerber Van der Graaf

## BUGS

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