automap model defaults

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

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