[GRASSLIST:9736] Re: filtering with FFT

[Martin Landa]

Hi,

I have tried to reproject the data to a UMN location. I get similar
wrong result, see the attached image. Is it really necessary to make
it in XY location. FFT should not affect geographic coordinates(?).
>From my point of view it seems like a bug.

Martin

2005/12/23, Markus Neteler <neteler at itc.it>:
> Martin,
>
> I have made these steps
>
>  g.region rast=tm1
>  i.fft in=tm1 real=tm1_r imag=tm1_i --o
> # g.region rast=tm1_r
> # r.circle -b out=ff coord=-769058,-988168 max=1550 --o
>  r.circle -b out=ff coord=-769058,-988168 max=10550 --o
>  d.rast tm1_r
>  d.rast -o ff
>
>  r.mapcalc 'mymask=if(isnull(ff),1,null())'
>  g.rename rast=mymask,MASK
>  i.ifft real=tm1_r imag=tm1_i out=tm1_hp --o
>  g.remove rast=MASK
> # g.region rast=tm1
>  r.colors map=tm1_hp col=grey.eq
>  d.rast tm1
>  d.rast tm1_hp
>
> and get the same ugly result.
>
> I suspect that 'krovak' with it's negative coordinates may be
> the case to let misbehave i.[i]fft.
>
> You may reproject to an UTM location and try again.
> If this works, we have to understand what i.[i]fft doesn't
> work with negative coordinates. If it doesn't work, the
> problem is more generic.
>
> Markus
>
> On Thu, Dec 22, 2005 at 09:06:26PM +0100, Martin Landa wrote:
> > Hi Markus,
> >
> > > can you put a mini location somewhere to play?
> >
> > the dataset which I use for lessons "Image processing" [1] (only in
> > Czech) at my university
> > is available at [2].
> >
> > [1] http://gama.fsv.cvut.cz/wiki/index.php/Zpracov%C3%A1n%C3%AD_obrazov%C3%BDch_dat
> >
> > [2]
> > http://grass.fsv.cvut.cz/~martin/vyuka/zzoz/datasety/
> >
> > Best regards, Martin
> >
> > PS: merry Christmas all GRASS developers/users...
> >
> > >
> > > Markus
> > >
> > > On Mon, Dec 19, 2005 at 10:38:43PM +0100, Martin Landa wrote:
> > > > Hi all,
> > > >
> > > > according to OSS GIS: A GRASS GIS Approach (see page 243) I am trying
> > > > to apply high pass filter with FFT. I always get a strange result
> > > > image (see the attached file).
> > > >
> > > > g.region rast=tm1
> > > > i.fft in=tm1 real=tm1_r imag=tm1_i
> > > > g.region rast=tm1_r
> > > > r.circle -b out=ff coord=-769058,-988168 max=1550
> > > > r.mapcalc 'MASK=if(isnull(ff),1,null())'
> > > > i.ifft real=tm1_r imag=tm1_i out=tm1_hp
> > > > g.remove rast=MASK
> > > > g.region rast=tm1
> > > > r.colors map=tm1_hp col=grey.eq
> > > > d.rast tm1_hp
> > > >
> > > > I don't know where I am wrong ... Does anyone have the same problem?
> > > >
> > > > Thanks for help, best regards,
> > > >
> > > > Martin
> > >
> > >
> > >
> > > --
> > > Markus Neteler     <neteler itc it>       http://mpa.itc.it
> > > ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
> > > MPBA - Predictive Models for Biol. & Environ. Data Analysis
> > > Via Sommarive, 18        -       38050 Povo (Trento), Italy
> > >
>
> --
> Markus Neteler     <neteler itc it>       http://mpa.itc.it
> ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
> MPBA - Predictive Models for Biol. & Environ. Data Analysis
> Via Sommarive, 18        -       38050 Povo (Trento), Italy
>
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