Oh, geostatistics and its funny naming conventions!
I see local models vs. global models as a completely different modelling
aspect (model decision, basically) then the SK/OK/UK differences. When
building on the same tradition / body of literature you quote: in that
case KED would be a special form of UK, having only a single
non-coordinate predictor called 'external drift'.
In my eyes (and that of the literature with more mathematical
statistical grounding, such as Cressie 1993 and others), the difference
between SK on the one hand and OK/UK on the other is that SK assumes
that you know the mean or mean structure. SKlm is then residual kriging
added to a known mean function.
In the gstat R package you obtain SK by specifying a beta value (for the
mean); SKlm by specifying one or more predictors and passing the (known)
regression coefficients as beta; you obtain OK/UK by not specifying
beta; a formula ending on ~1 results in OK with an unknown mean only.
Ah, and then SK = simple kriging, OK = ordinary kriging, UK = universal
kriging.
--
Edzer
Cutberto Uriel Paredes Hernández wrote:
Dear Edzer,
Would it be correct to say then that if a neighbourhood is specified
in the krige command the result would be that of Kriging with an
External Drift (KED), otherwise it would be that of Simple Kriging
with varying local means (SKlm)?
Apologies for posting on this thread but I was about to post a
similiar question.
Thanks, Cutberto.
2010/1/26 Edzer Pebesma <edzer.pebe...@uni-muenster.de>:
Yes, that is right.
Els Verfaillie wrote:
Dear list,
I want to use Kriging with an external drift for a sedimentological
dataset
of grain-size that has a linear relation with the depth.
Am I correct that when I set a 'maxdist' using the krige command, that a
trend for the primary variable (grain-size) is calculated as a local
linear
function of the secondary variable (depth)? Is this function thus
different
for each interpolation window?
d50.ked.dir50 <- krige(D50F~depth, locations=ds50, newdata=Depth,
model=d50.fit.var.50, nmin=2, nmax=16, maxdist=9000)
Thank you for your help.
Best regards,
Els Verfaillie
______________________________________________
Dr. Els Verfaillie
Carto-GIS cluster
Ghent University (UGent) - Department of Geography
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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.pebe...@wwu.de
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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.pebe...@wwu.de
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