[R-sig-Geo] nugget in variogram

[Edzer Pebesma]

Sorry, this was too fast again:

v[1,"gamma"]
# or
v.m$psill[1]

are estimators of the nugget variance;

v.m$psill[1] / sum(v.m$psill)

is an estimator of the nugget-to-sill ratio.

On 09/30/2010 06:39 PM, Edzer Pebesma wrote:
> 
> 
> On 09/30/2010 04:13 PM, Arantzazu Blanco Bernardeau wrote:
>> Hello everybody
>> I am new on geostatistics so maybe my question is trivial or is
>> already answered (I can not find the solution in the thread list). I
>> have a variogram where I did not fix the nugget, because doing it
>> was giving "singular models". I would like to know the nugget ratio
>> of my variograms but I don't know how to get then the nugget value.
>> So I did look in the output of variogram and did take the minimum
>> value of gamma. Is this correct?
> 
> Well, it's not the usual way, where you would fit a model:
> 
> library(gstat)
> data(meuse)
> coordinates(meuse) = ~x+y
> v = variogram(log(zinc)~1, meuse)
> v.m = fit.variogram(v, vgm(1, "Sph", 500, 1))
> v[1, "gamma"] # your estimator:
> plot(v, v.m)
> v.m$psill[1] / sum(v.m$psill) # the usual estimator:
> 
> Only when you have plenty of measurements at very short distances
> apart, I can imagine you would use the sample variogram (v) value.
> 
>> Thanks very much for your attention. 
>>  		 	   		  
>> 	[[alternative HTML version deleted]]
>>
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> 

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de