[GRASSLIST:2409] Re: The g3.region settings ....

[Markus Neteler]

On Thu, Jan 29, 2004 at 05:50:58PM +0100, Geotronix wrote:
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> * giovedì 29 gennaio 2004, alle 10:44, Markus Neteler scrive:
> > On Wed, Jan 28, 2004 at 01:40:06PM +0100, Geotronix wrote:
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> > > Hi,
> > > 
> > > I'm trying to get s.vol.rst to work for the computation of rainfall map
> > > using a 50m resolution cell (1000x1000 cells grid).
> > > Now, the site file that's input for s.vol.rst has 4 columns
> > > x|y|z|%rainfall(mm/year)
> > > 
> > > When I tried to launch s.vol.rst the first time it told me that I had to
> > > set the 3D region. SO I launched g3.createregion which reead the
> > > defaults from the current 2D region. I gave him the following options:
> > > 
> > > g3.createregion t=2500 b=0 dres=1
> > > 
> > > as to resemble:
> > > 
> > > t=2500 --> max altitude in meters that I have on my dem;
> > > b=0  --> min altitude on my dem ;
> > > dres=1 -->vertical resolution on 1 meter.
> > 
> > It's probably much better, if you eventually just want to extract a 2D
> > rainfall map, to run the computation in a single-layer volume:
> > 
> > g3.createwind t=2500 b=0 dres=2500
> > 
> >  t=2500 --> max altitude in meters that I have on my dem;
> >  b=0  --> min altitude on my dem ;
> >  dres=2500 -->vertical resolution 2500 meter.
> > 
> > Then s.vol.rst ...
> > 
> > Please report if this is faster.
> > 
> >  Markus Neteler
> 
> You're right! It's a lot faster.... but what does it change pratically
> form using a dres=2500 instead of dres=1? IS the result diffrent?

Note, I am not the author of s.vol.rst.

The author once explained to me that, when being interesting in a
2D output map, it is not necessary to calculate the temporal volume
in descrete layers. so I expect an identical result.


> There a re a few things that are not stated in the docs of s.vol.rst and
> r.surf.rst.
> What unit measure are used when I state smooth=1; tension=50 and
> zmult=50. Are these percent values. If I don't know what units I'm
> dealing with,how can I state some sort of mathimatical relation between
> the values of these parameters and the geological/meteorological problem
> I'm dealing with.

I write in CC to the authors, they may have an answer for this.

> Let me make an example. Of my 25 stations, most of them have low
> variance of the mean while a few have a very high variance. This lets me
> think that I could use the smooth parameter set to zero for all the low
> variance rainfall stations while I should use a higher smoothing for
> the stations that have I higher variance. Is this conceptually correct?
> But how do I relate the variance to the smoothing parameter?
> 
> Thanks


Markus