1i.fft(1) GRASS GIS User's Manual i.fft(1)
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6 i.fft - Fast Fourier Transform (FFT) for image processing.
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9 imagery, transformation, Fast Fourier Transform
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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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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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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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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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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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84 i.cca, g.gui.iclass, i.ifft, i.pca
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87 David Satnik, GIS Laboratory, Central Washington University
88 Glynn Clements (FFTW support)
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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 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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100GRASS 7.8.5 i.fft(1)