[GRASS-dev] Re: [GRASS-SVN] r34353 - in grass/trunk/imagery: i.fft i.ifft

[Glynn Clements]

Markus Neteler wrote:

> > Author: glynn
> > Date: 2008-11-17 20:41:17 -0500 (Mon, 17 Nov 2008)
> > New Revision: 34353
> >
> > Removed:
> >   grass/trunk/imagery/i.fft/fft_colors.c
> >   grass/trunk/imagery/i.fft/globals.h
> >   grass/trunk/imagery/i.fft/local_proto.h
> >   grass/trunk/imagery/i.fft/orig_wind.c
> >   grass/trunk/imagery/i.fft/save_fft.c
> >   grass/trunk/imagery/i.ifft/globals.h
> >   grass/trunk/imagery/i.ifft/local_proto.h
> >   grass/trunk/imagery/i.ifft/orig_wind.c
> > Modified:
> >   grass/trunk/imagery/i.fft/Makefile
> >   grass/trunk/imagery/i.fft/i.fft.html
> >   grass/trunk/imagery/i.fft/main.c
> >   grass/trunk/imagery/i.ifft/Makefile
> >   grass/trunk/imagery/i.ifft/i.ifft.html
> >   grass/trunk/imagery/i.ifft/main.c
> > Log:
> > Rewrite i.fft, i.ifft
> > Output maps are FP
> > Don't use cell_misc/<map>/fft{real,imag} files, use the output maps
> > Don't rescale to powers of two (not needed with FFTW)
> > Use fft2() with FFTW-style interleaved array, not fft() with separate real/imaginary arrays
> > Miscellaneous clean-up
> 
> backport this?

No. It's an incompatible change. The output of the old i.fft won't
work with the new i.ifft and vice versa.

The old i.fft stored the actual FFT coefficients in the files
cell_misc/<map>/fft{real,imag}; the actual maps were just visual
representations which could be viewed with d.rast. The old i.ifft used
the data in the fft{real,imag} files, ignoring the maps' contents (it
would explicitly read the mask file, allowing you to perform filtering
by setting a mask before running i.ifft).

The new i.fft stores the data in the maps, and the new i.ifft reads
the maps. So you can perform filtering by using e.g. r.mapcalc on the
FFT maps.

-- 
Glynn Clements <glynn at gclements.plus.com>