maxdist for kriging with an external drift

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 Hern?ndez 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.pebesma at 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

--
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

-- 
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