[GRASSLIST:81] Re: interpolated values out of range

[Stefan Istvan]

On Tue, 2006-03-14 at 12:12 +0100, Markus Neteler wrote:
> On Tue, Mar 14, 2006 at 12:03:06PM +0100, Stefan Istvan wrote:
> > Hello List!
> > 
> > I have some vector points with a value attached to them, and I would
> > like to interpolate a raster surface from them. 
> > My problem is that the resulting raster map contains values that are
> > smaller then the minimum value of my vector points.
> > I set the smooth paramter to 0, in order to the resulting surface cross
> > exactly the vector points.
> > I also set the tension paramter to 180 because during the interpolation
> > grass said that overshoot occures and suggested to increase tension.
> > The imported vector point values range from 10-35900, but on the
> > resulting raster map there are values far below zero (-2000).
> > I also tried so set smooth to default (0.1), but still get values below
> > 0.
> > Is there any method to calculate the value of tension and smooth, or
> > just trying?
> 
> In GRASS 6.1-CVS, cross validation was added as flag to optimize
> tension and smoothing.
> 
> See: 
>  http://grass.itc.it/grass61/manuals/html61_user/v.surf.rst.html
>  -> Cross validation procedure
> 
> Markus
> 
Thank you, I've tried it, but still need help, because I don't
understand exactly what sould I do.
I performed cross validation with this command:
v.surf.rst -c input=szennyezes2d05meteren cvdev=valid
I got a vector file named valid.
Now what is the next step to calculate proper parameters for
interpolation?

Thank you,
Istvan