i.fft(1grass) GRASS GIS User's Manual i.fft(1grass)
NAME
i.fft - Fast Fourier Transform (FFT) for image processing.
KEYWORDS
imagery, transformation, Fast Fourier Transform
SYNOPSIS
i.fft
i.fft --help
i.fft input=name real=name imaginary=name [--overwrite] [--help]
[--verbose] [--quiet] [--ui]
Flags:
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of input raster map
real=name [required]
Name for output real part arrays stored as raster map
imaginary=name [required]
Name for output imaginary part arrays stored as raster map
DESCRIPTION
i.fft is an image processing program based on the FFT algorithm given
by Frigo et al. (1998), that processes a single input raster map layer
(input) and constructs the real and imaginary Fourier components in
frequency space.
NOTES
The real and imaginary components are stored into the real and imagi-
nary raster map layers. In these raster map layers the low frequency
components are in the center and the high frequency components are to-
ward the edges. The input need not be square. A color table is as-
signed to the resultant map layer.
The current geographic region and mask settings are respected when
reading the input file. The presence of nulls or a mask will make the
resulting fast Fourier transform invalid.
EXAMPLE
North Carolina example:
g.region raster=lsat7_2002_70
i.fft input=lsat7_2002_70 real=lsat7_2002_70.real imaginary=lsat7_2002_70.imag
# set region to resulting FFT output map (due to new FFT coordinate space):
g.region raster=lsat7_2002_70.real -p
d.mon x0
d.rast lsat7_2002_70.real
d.rast lsat7_2002_70.imag
REFERENCES
• M. Frigo and S. G. Johnson (1998): "FFTW: An Adaptive Software
Architecture for the FFT". See www.FFTW.org: FFTW is a C sub-
routine library for computing the Discrete Fourier Transform
(DFT) in one or more dimensions, of both real and complex data,
and of arbitrary input size.
• John A. Richards, 1986. Remote Sensing Digital Image Analysis,
Springer-Verlag.
• Personal communication, between program author and Ali R. Vali,
Space Research Center, University of Texas, Austin, 1990.
SEE ALSO
i.cca, g.gui.iclass, i.ifft, i.pca
AUTHOR
David Satnik, GIS Laboratory, Central Washington University
Glynn Clements (FFTW support)
SOURCE CODE
Available at: i.fft source code (history)
Accessed: unknown
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GRASS 7.8.7 i.fft(1grass)
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