On 02/21/2011 10:07 PM, yong.t...@optusnet.com.au wrote: > Dear All, > > I plan to use gstat to do some 3D kriging on a spatio-temporal dataset I have > collected to look at the spatio-temporal distributions of soluble nutrients > in shallow groundwater. > I did read some papers such as written by Heuvelink and De Inco, quite > impressed by the outcomes and curiously want to do my own. When I ran > demo(pcb) and demo(wind), found the outputs were slightly different from what > I expected. they did not calculate the temporal semivariance (or maybe they > did but I just did not know where they are). > In the literature, people always talk about the combination of spatial > variance and temporal variance, such product and product-sum functions, but I > did not see them in the demo(pcb) and demo(wind). > > Any experts in the area giving me a full procedure of using gstat to do 3D > kriging is highly appreciated. > py demo(pcb) essentially uses cokriging, and sees the (4) time replicates as correlated, but different variables. Spatial correlation is then modelled in the direct variograms, spatio-temporal correlation in the cross variograms.
demo(wind) in package gstat defines a separable covariance function (function covfn) similar to the one used by Haslett and Raftery, that is passed to krige0. You could define your own function, such as a product-sum model, here. In package spacetime the same example is worked out (see the vignette), using spatio-temporal data structures. In principle you can mimic product-sum variograms by the metric (3D) variogram model in 3D kriging in gstat by setting the right anisotropy ranges to values very close to zero. > Regards, > > Yong Li > > ps. > I used to be on the list of r-sig-geo, but was knocked out by unknown > reasons. wish this time I can make it. I'll keep them informed. Maybe your questions were too hard. ;-) > > _______________________________________________ > Geostatistics mailing list > geostatist...@52north.org > http://list.52north.org/mailman/listinfo/geostatistics > http://geostatistics.forum.52north.org -- 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 _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo
