[GRASSLIST:1572] Re: interpolate nominal values

[sturm at datacomm.ch]

At 12:31 08.03.2001 +0000, you wrote:
>Hi list,

>I want to interpolate nominal data (soil types as point information). 
>Which possibilities do I have, what's the best method? -Any 
>experiences, suggestions?

Hi Susanne
I made very good experiences with s.surf.rst (regularised splines with tension).
I used it for the interpoaltion of rainfall point data. I wrote a small perl
script with which you can determine the best available interpolation model (comparing
IDW and RST) by using the cross validation method. You will have to 'play' with
the RST parameters in order to get quite accurate results. In the best cases
I achieved a correlation coefficient of 0.9 for the RST model. But the cross
validation approach took over a week processor time to compute the best fit...

If you'd like I can post you the perl script (but you'll have to adapt it to
your own needs)

Bernhard Sturm
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CDE, Centre for Development and Environment, University of Berne