[R-sig-Geo] quick question re: fit.variogram in gstat

[Kerry Ritter]

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: kerryr at sccwrp.org
>
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-- 
**********************
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: kerryr at sccwrp.org