[GRASSLIST:2397] Re: The g3.region settings ....

[Geotronix]

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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

BTW.

I just tried some new settings with s.vol.rst and I'm getting every time
more puzzled....

He are two tries I gave to s.vol.rst using a 50m resolution DEM, with
area 1000x1000 cells, as "cellin" to compute my rainfall data using 25
mean annual rainfall values for 25 rainfall stations:

a) tension=50 smoothing=0 zmult=1 gave me a map that did not resemble
any altimetric influence. The mean thickness of the rainfall water
table, spread over the 74Km^2 area (after it was masked down to from
original 1600Km^2 using the "maskmap" option) is 1109mm

b) tension=50 smoothing=0 zmult=50 gave me a complete diffrent map where
you can see that topografic influence on the rainfall. To my surprise
the mean water table was 1110mm!! Only 1mm difference for two complete
diffrent maps. 

The problem is that I'm not understanding how zmult influences the
application of the altimetric information to the interpolating
algorithmn.

Another thing is: My highest altimetric rainfall station is at 900 meters
above sea level (which has a mean annual rainfall of 1250mm). 
I have many mountainous areas that reach 1300 meters
a.s.l. and s.vol.rst is not computing any rainfall value higher than
1250mm/year. Shouldn't it be predicting higher values for higher
altitudes?

Thanks.
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