This is the command i.fftgrass that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
PROGRAM:
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 imaginary raster map
layers. In these raster map layers the low frequency components are in the center and the
high frequency components are toward the edges. The input need not be square. A color
table is assigned 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
REFERNCES
· M. Frigo and S. G. Johnson (1998): "FFTW: An Adaptive Software Architecture for
the FFT". See www.FFTW.org: FFTW is a C subroutine 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 progam author and Ali R. Vali, Space Research
Center, University of Texas, Austin, 1990.
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