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
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.
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.
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
- 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 program author and Ali R. Vali,
Space Research Center, University of Texas, Austin, 1990.
i.cca,
g.gui.iclass,
i.ifft,
i.pca
David Satnik, GIS Laboratory,
Central Washington University
Glynn Clements (FFTW support)
SOURCE CODE
Available at:
i.fft source code
(history)
Latest change: Thursday Feb 03 11:10:06 2022 in commit: 547ff44e6aecfb4c9cbf6a4717fc14e521bec0be
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© 2003-2023
GRASS Development Team,
GRASS GIS 8.2.2dev Reference Manual