[R-sig-Geo] automap model defaults

[Mark Connolly]

On 04/15/2010 07:42 AM, Paul Hiemstra wrote:
> Mark Connolly wrote:
>> I was wondering what is behind the selection of the default models 
>> tried by autofitVariogram (model=c("Sph","Exp","Gau","Ste")).  For 
>> example, why was linear model left out?
>>
>> Thanks
>>
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> Hi Mark,
>
> These models are the models that are most often used, so it seemed 
> logical to use these ones. But why do you want to include the linear 
> model specifically?
>
> cheers,
> Paul
>
Only because it sometimes results in a lower SSError.  I guess that is 
my real question: why wouldn't I want to try the linear model in the 
set?  The field I am looking at is a layered ag field in a coastal 
plain, and the five depth layers (which extend to less than a meter from 
the surface) I am looking at are often fairly homogeneous for specific 
properties.  Some of property values I am fitting produce a linear model 
as the best fit in a specific layer.  (Although sometimes when this is 
the case, the linear model is just barely better and than the next-best 
non-linear model.)

I assume the selection of the default models is not arbitrary, but I 
lack the experience to include/exclude linear models in the best fit 
search.  Best to stick with the default?

Thanks,
Mark