[R-sig-Geo] Doubts about kriging

[Rubén Roa-Ureta]

GEMA FERNANDEZ-AVILES CALDERON wrote:

> Dear list,
>  
> I have two problem and I would like to know you opinion.
>  
> 1.  I am kriging 6 environmental variables, SO2, NOx, O3, CO, NO, 
> PM10, to built and enviromental index in R. I have standardized the 
> observed values and I am implementing in geoR  the function likfit to 
> obtain the parameter lambda (Box-Cox transformation) to see if the 
> standarized variables are normal. But I have error using the likfit 
> function. It could be that the error arise because the standarized 
> variables contain negative values?
>   
You have to tell us what the error message says. The negative values of 
your variable should not be the problem.
Another thing. The lambda parameter is there not to 'see' if the 
regionalised variable is normal. The lambda parameter is there to *make* 
the regionalised variable as close to normal as possible.

>  
> 2. I have values of the 6 variables at 25 locations but I want to use 
> a linear combination of the six variables to deal with only a 
> variable. Finally, I want to interpolate this only variable in several 
> sites where I have not observed data. What do you think is better? - 
> To interpolate each one of the six variables and then elaborate the 
> linear combination.
> - Or to elaborate a linear combination with the observed values and 
> finally krige the linear combination.
>   
If the variables are correlated you can use your first option doing a 
principal component analysis, and then kriging the first component.
HTH
R.