[R-sig-Geo] Package for automatic interpolation

[Paul Hiemstra]

Hi Thomas,

The automatic fitting procedure checks a range of possible variogram 
models, including Spherical, Exponential, Gaussian and Matern models. 
Each of these models could lead to a singular model fit. The fitting 
function in gstat (fit.variogram) says the following on singular model fits:

"""On singular model fits: If your variogram turns out to be a flat, 
horizontal or sloping line, then fitting a three parameter model such as 
the exponential or spherical with nugget is a bit heavy: there's an 
infinite number of possible combinations of sill and range (both very 
large) to fit to a sloping line. In this case, the returned, singular 
model may still be useful: just try and plot it. Gstat converges when 
the parameter values stabilize, and this may not be the case. Another 
case of singular model fits happens when a model that reaches the sill 
(such as the spherical) is fit with a nugget, and the range parameter 
starts, or converges to a value smaller than the distance of the second 
sample variogram estimate. In this case, again, an infinite number of 
possibilities occur essentially for fitting a line through a single 
(first sample variogram) point. In both cases, fixing one or more of the 
variogram model parameters may help you out. """'

regards,
Paul

Thomas Adams schreef:
> Paul,
>
> This is outstanding; thank you very much! BTW, I noticed that when I 
> run your example that I get:
>
> Warning: singular model in variogram fit
>
> …actually, 2 such warnings with the OK example, and 1 with the UK 
> example. Are you seeing these too? Otherwise, the results look fine…
>
> Thanks again for your contribution!
>
> Regards,
> Tom
>
>
> Paul Hiemstra wrote:
>> Dear r-sig-geo,
>>
>> In the course of my PhD I have written a R package that performs 
>> automatic interpolation (kriging) and might be interesting for other 
>> people. I work on real-time automatic interpolation of radioactivity 
>> levels. It depends heavily on the gstat pacakge written by Edzer 
>> (Pebesma, he is my supervisor). If people are interested in this 
>> package, it can be downloaded from 
>> http://intamap.geo.uu.nl/~paul/Downloads.html. If you have any 
>> comments, complaints or suggestions please do not hesitate to e-mail me.
>>
>> Some sample code:
>> library(automap)
>> data(meuse)
>> coordinates(meuse) = ~x+y
>> data(meuse.grid)
>> gridded(meuse.grid) = ~x+y
>> kr.ok = autoKrige(log(zinc)~1, meuse, meuse.grid)
>> plot(kr.ok)
>> kr.uk = autoKrige(log(zinc)~sqrt(dist), meuse, meuse.grid)
>> plot(kr.uk)
>>
>> cheers,
>> Paul
>>
>>   
>
>


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: 	+31302535773
Fax:	+31302531145
http://intamap.geo.uu.nl/~paul