Difference between revisions of "Geopsy: Fast Fourier Transform"
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| − | All Fourier Transforms in geopsy are based on the algorithms developed by Matteo Frigo and Steven G. Johnson (MIT) called the "Fastest Fourier Transform in the West" and encapsulated in FFTW library. | + | All [[Wikipedia: Fourier_Transform|Fourier Transforms]] in geopsy are based on the algorithms developed by Matteo Frigo and Steven G. Johnson (MIT) called the "Fastest Fourier Transform in the West" and encapsulated in FFTW library. This is a highly optimized library able to handle any number of samples (not only a power of 2) |
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| + | A Fourier transform does not alter the signal, i.e. an inverse transform reproduces the complete original signal without any loss. Hence, in ''geopsy'' graphical interface, a Fourier transform is not considered as a [[Geopsy: Waveform Menu|waveform processing]]. The switch from time to frequency domain and vice-versa is located in [[Geopsy: View menu|View menu]]. | ||
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| + | When [[Geopsy: File menu#Export|exporting]] to an [[Geopsy: Supported file formats#ASCII Multi column (rw)|ASCII Multi-column file]] (and only for that format), the current domain is taken into account. The Fourier spectrum is exported with two columns per channel (real and imaginary). The total number of lines of the produced file is approximately half of the number of samples (difference between odd and even number of samples). | ||
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== External references == | == External references == | ||
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[http://www.fftw.org FFTW] | [http://www.fftw.org FFTW] | ||
Latest revision as of 13:31, 12 March 2010
All Fourier Transforms in geopsy are based on the algorithms developed by Matteo Frigo and Steven G. Johnson (MIT) called the "Fastest Fourier Transform in the West" and encapsulated in FFTW library. This is a highly optimized library able to handle any number of samples (not only a power of 2)
A Fourier transform does not alter the signal, i.e. an inverse transform reproduces the complete original signal without any loss. Hence, in geopsy graphical interface, a Fourier transform is not considered as a waveform processing. The switch from time to frequency domain and vice-versa is located in View menu.
When exporting to an ASCII Multi-column file (and only for that format), the current domain is taken into account. The Fourier spectrum is exported with two columns per channel (real and imaginary). The total number of lines of the produced file is approximately half of the number of samples (difference between odd and even number of samples).
