gstat::krige() - regression kriging vs. kriging with external drift
On 14/11/15 17:32, Bede-Fazekas ?kos wrote:
Dear List, dear Edzer, is it correct if I use the term "regression kriging" when I run this function?: kriged_value <- gstat::krige(z ~ x + y, [...])@data$var1.pred Or should I call it "kriging with external drift" (or "universal kriging" if x and y are coordinates), and use the term "regression kriging" only in the case of running this?: linear_model <- lm(z ~ x + y, [...]) residuals <- linear_model$residuals kriged_residuals <- gstat::krige(residuals ~ 1, [...])@data$var1.pred kriged_value <- linear_model$fitted.values + kriged_residuals
For what it's worth, my opinion: I would call it universal kriging, in line with the software you're using (which I wrote):
x = krige(zinc~x+y, meuse, meuse.grid, m)
[using universal kriging] Most of the (older) literature associates external drift kriging with a single external drift variable (e.g. Goovaerts), and universal kriging with using coordinates as covariates. The statistician might call everything best linear unbiased prediction under the the general linear model y = X beta + e, with a spatial covariance function describing the covariance of e, and in that perspective both methods are equivalent. I'm not the person to tell what regression kriging is and what it is not, but it might include the above models as well as those where trend fitting and residuals are done in different steps, and potentially under different assumptions for e.
Edzer Pebesma Institute for Geoinformatics (ifgi), University of M?nster, Heisenbergstra?e 2, 48149 M?nster, Germany; +49 251 83 33081 Journal of Statistical Software: http://www.jstatsoft.org/ Computers & Geosciences: http://elsevier.com/locate/cageo/ Spatial Statistics Society http://www.spatialstatistics.info -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 490 bytes Desc: OpenPGP digital signature URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20151125/b25e72fb/attachment.bin>