1i.fft(1)                      Grass User's Manual                     i.fft(1)
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NAME

6       i.fft  - Fast Fourier Transform (FFT) for image processing.
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KEYWORDS

9       imagery, transformation, Fast Fourier Transform
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SYNOPSIS

12       i.fft
13       i.fft --help
14       i.fft  input=name  real=name  imaginary=name   [--overwrite]   [--help]
15       [--verbose]  [--quiet]  [--ui]
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17   Flags:
18       --overwrite
19           Allow output files to overwrite existing files
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21       --help
22           Print usage summary
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24       --verbose
25           Verbose module output
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27       --quiet
28           Quiet module output
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30       --ui
31           Force launching GUI dialog
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33   Parameters:
34       input=name [required]
35           Name of input raster map
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37       real=name [required]
38           Name for output real part arrays stored as raster map
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40       imaginary=name [required]
41           Name for output imaginary part arrays stored as raster map
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DESCRIPTION

44       i.fft is an image processing program based on the FFT  algorithm  given
45       by  Frigo et al. (1998), that processes a single input raster map layer
46       (input) and constructs the real and  imaginary  Fourier  components  in
47       frequency space.
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NOTES

50       The  real  and imaginary components are stored into the real and imagi‐
51       nary raster map layers.  In these raster map layers the  low  frequency
52       components  are  in  the  center  and the high frequency components are
53       toward the edges.  The input need not  be  square.  A  color  table  is
54       assigned to the resultant map layer.
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56       The  current  geographic  region  and  mask settings are respected when
57       reading the input file. The presence of nulls or a mask will  make  the
58       resulting fast Fourier transform invalid.
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EXAMPLE

61       North Carolina example:
62       g.region raster=lsat7_2002_70
63       i.fft input=lsat7_2002_70 real=lsat7_2002_70.real imaginary=lsat7_2002_70.imag
64       # set region to resulting FFT output map (due to new FFT coordinate space):
65       g.region raster=lsat7_2002_70.real -p
66       d.mon x0
67       d.rast lsat7_2002_70.real
68       d.rast lsat7_2002_70.imag
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REFERENCES

71           ·   M.  Frigo and S. G. Johnson (1998): "FFTW: An Adaptive Software
72               Architecture for the FFT". See www.FFTW.org: FFTW is a  C  sub‐
73               routine  library  for  computing the Discrete Fourier Transform
74               (DFT) in one or more dimensions, of both real and complex data,
75               and of arbitrary input size.
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77           ·   John  A. Richards, 1986. Remote Sensing Digital Image Analysis,
78               Springer-Verlag.
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80           ·   Personal communication, between program author and Ali R. Vali,
81               Space Research Center, University of Texas, Austin, 1990.
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SEE ALSO

84        i.cca, g.gui.iclass, i.ifft, i.pca
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AUTHOR

87       David Satnik, GIS Laboratory, Central Washington University
88       Glynn Clements (FFTW support)
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SOURCE CODE

91       Available at: i.fft source code (history)
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93       Main  index | Imagery index | Topics index | Keywords index | Graphical
94       index | Full index
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96       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
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100GRASS 7.8.2                                                           i.fft(1)
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