nugget in variogram
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 M?nster Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de http://www.52north.org/geostatistics e.pebesma at wwu.de