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.