PIVMat Function Reference | << Prev | Next >> |

Fourier temporal filter of a vector/scalar field time series

VF = **tempfilterf**(V, IND) applies a Fourier temporal band-pass filter to
the vector or scalar fields time-series V at the frequency specified by
the integer index IND. The output field VF is a time series containing
the spatial structure of the (eigen)mode corresponding to this frequency.
The frequency index IND can be determined from the peaks in the
temporal Fourier spectrum, by using the function tempspecf with option
'peaks'.
VF = **tempfilterf**(V, IND) also works when IND is an array of integers.
For instance, IND = [IND1, IND2, IND3 ...] applies a band-pass filters
for the frequency indices IND1, IND2, IND3 ...
If IND is an interval in the form IFIRST:IEND, it applies a band-pass
filtering for the range of frequency indices between IFIRST and IEND
(i.e. it removes all the frequencies outside the interval IND). If
IFIRST=1, this corresponds to a low-pass filter; if IEND==LENGTH(VF)/2,
this corresponds to a high-pass filter.
Algorithm: **tempfilterf** Fourier-transforms the input fields V in the
frequency doamin, applies a mask function (=1 for the frequencies
specified by the indices IND, and =0 otherwise), and Fourier transform
back in the time domain.
Note that if IND is a single integer, the filter is a Dirac in
frequency, so the resulting output time-series is strictly periodic.
In this case, only the first period is of interest: it can be recovered
using the option VF = **tempfilterf**(V, IND, 'phaseaverf'). On the other
hand, if IND contains more than one frequency index, the result is not
periodic in general.
VF = **tempfilterf**(V, IND, 'remove') removes all the frequency indices
specified by IND (again, IND may be a scalar or an array of integers).
This option just takes the complementary of the intial mask function.
This is useful to remove the oscillations due to an unwanted vibration
in the acquisition system.
By default, the filtering applies to both positive and negative
frequencies, so that the resulting filtered time series is real-valued.
It is possible to filter only the positive frequencies by using the
following syntax: VF = **tempfilterf**(V, IND, 'complex').
In this case, the output field VF is complex-valued, i.e. the arrays
VF.vx, VF.vy etc contain both the amplitude and phase of the filtered
fields. Note that such complex fields can be used for usual computations
(averf, filterf etc), but cannot be directly displayed using showf.
See operf to extract the real or imaginary part of VF in order to
display it using showf.
If no output argument specified, the filtered field is displayed.

**Example**
Displays the spatial structure of an eigenmode
mv = loadvec('*.vc7');
tempspecf(mv, 200, 'peaks');
% from this plot, select the index of the peak of interest, e.g. 35
m = **tempfilterf**(mv, 35);
showf(m, 'rot');

**See Also**
tempspecf, phaseaverf, smoothf, operf, showf.
Published output in the Help browser
showdemo **tempfilterf**

Previous: tempcorrf | Next: tempspecf |

2005-2017 PIVMat Toolbox 4.10