[R-sig-Geo] Fitting nested variograms to empirical variograms

[Edzer J. Pebesma]

Eliot McIntire wrote:

>
> gstat: I can run nested models using
> F2.BA1.fit = fit.variogram (F2.BA1.variogram, vgm(psill=33,"Lin",6, 
> add.to  = vgm(psill=33,"Lin",6, nugget=20) )
>                 , print.SSE=T, fit.sills=T, fit.ranges=T )
>
>
> but I never seem to get a good fit, i.e., it always fails to fit the  
> empirical variogram.
>
> If anyone has a solution, I also need to calculate the Residual Sums 
> of  Squares to test for the relative fit.

The problem is your starting values for the ranges. Use the values that you
fit `by eye' from the sample variogram; they should be sufficiently distinct
(and present in the sample variogram) for gstat to fit them with success.

Also, be aware that the linear model with range is not a valid variogram
model for data in more than one dimension.

Best regards,
--
Edzer