What you see is the range parameter; as the Gaussian model reaches the sill asymptotically, the value sqrt(3) * a is often used as the "effective range", or distance value where 95% of the (partial) sill is reached. Just plot the curve of 1-exp(-(h/a)^2) to see why this is so.
On 08/09/2010 05:06 PM, Kerry Ritter wrote: > I have a follow up question regarding the range parameter specified for > the gaussian variogram model in gstat.. > First, thank you to Jaime Grion who riplied... > > Dear Kerry, if you write in the option model "Gau" you just have to > specify 200 [for the range]. > > However, when I fit the variogram and the fitted value returns "200" as > the range parameter, the variogram looks like the true range exceeds > 200. Is the returned range parameter the "practical range" = the value > at which this model reaches 95% of its asymptotic value or the value > where spatial correlation ceases to exist?. In Bivand, et. al's book > "Applied Spatial Data Analysis with R", the authors state that the > practical range for the gaussian variogram model is sqrt(3)*a where a is > the range parameter for most other models. So my question remains. Is > the fit giving me the range or the practical range? > > Thanks, > Kerry > > Kerry Ritter wrote: >> Hi all. I have what I hope is a quick question concerning the use of >> "fit.variogram" in"gstat". If you assume a a Spherical model for the >> variogram and the estimated range is say 200m and then you switch >> models to a Gaussian but want to keep the range fixed at 200m, would >> you specify 200 for the range parameter or 200/sqrt(3)? >> >> Thanks, >> Kerry >> >> ********************** >> Kerry Ritter, Ph.D. >> statistician >> Southern California Coastal Water Research Project >> 3535 Harbor Blvd., Suite 110 >> >> work: 714-755-3210 >> cell: 714-420-3346 >> fax: 714-755-3299 >> >> email: ker...@sccwrp.org >> >> _______________________________________________ >> R-sig-Geo mailing list >> R-sig-Geo@stat.math.ethz.ch >> https://stat.ethz.ch/mailman/listinfo/r-sig-geo >> > > -- 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@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
