[GRASS-user] Question about MODIS band 5 destriping?

Glynn Clements glynn at gclements.plus.com
Wed Apr 9 23:09:50 EDT 2008

Markus Neteler wrote:

> >  > I think that the strange i.fft file format is an obstacle here. AFAIK it
> >  > is not saved as "normal" raster file which limits the possibilities to
> >  > elaborate. Maybe I am wrong, don't quite remember well..
> >
> >  No, you're quite correct.
> >
> >  i.ifft ignores the actual input map, reading the data from the fftreal
> >  and fftimag files created by i.ifft. So you can't modify the i.fft
> >  output with e.g. r.mapcalc than use i.ifft on the result. The only
> >  modification which can be performed on the FFT data is masking; i.ifft
> >  reads the mask separately and applies it to the data.
> Could we change this for GRASS 7? Possibly there was a reason
> to implement it as private solution but hopefullyx we can work around
> that.

The main issue is that you can't store both the real and imaginary
components (or, alternatively, magnitude and phase) in a single map.

The other issues (e.g. the fact that an array of FFT coefficients
isn't actually geodata) can probably be fudged around.

Glynn Clements <glynn at gclements.plus.com>

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