[R-sig-Geo] Univeral kriging

[Ashton Shortridge]

Hi there,

good routines already exist in several R libraries for doing this. They will 
save you trouble in developing bug-free and efficient code. Check out gstat and 
maybe fields.

If you still want to implement kriging manually, these scripts, which I 
developed for a class exercise, might be a useful starting place. They are not 
there permanently, probably through the end of 2009:
http://www.msu.edu/~ashton/classes/866/notes/lect18/manual_krig.R
http://www.msu.edu/~ashton/classes/866/notes/lect18/covmodels.R

yours,

Ashton

On Monday 26 October 2009 07:56:36 TANKISO THEJANE wrote:
> R geo-helpers
>  
> i am new to r and would like you to help me as i am trying to go through
>  basic steps. I need to compute a predicted value at point (3,3) and its
>  variance given la set of locations and value. i want to make the code
>  generic for any size such that i would be able to estimate universal krige
>  at each point of grid (0,..,6) (0,..6). 
> the code
>  
> g = function(h) { return(0.1+3*(1-exp(-h/4)))}## variogram of exponential
>  form x = rbind(c(1,1),c(2,5),c(4,1),c(5,4))##4 observed locations
> x = rbind(x,c(3,3))  # Row five is the point at which we want to estimate.
> d = sqrt(x[,1]^2+x[,2]^2)##distance of the locations from the origin
> s = c(1,9,5,12)## values at the corresponding 4 locations
> ## pairsv = pair semivariogram
> pairsv = function(i,j) {
>   p1 = x[i,]
>   p2 = x[j,]
>   d = sqrt(sum((p1-p2)^2))
>   return(g(d))
> }
> G = matrix(0,4,4)
> for(i in 1:4) for(j in 1:4) G[i,j] = pairsv(i,j)
> X = matrix(0,4,3)
> for(i in 1:4) for(j in 1:3) X[i,j] = d[i]^(j-1)
> ##Asymmetric matrix
> Gu = rbind(cbind(G,X), cbind(t(X),matrix(0,3,3)))
> x
> gu = (1:7)*0
> gu
> for(i in 1:4) gu[i] = pairsv(i,5)
> for(i in 1:3) gu[i+4] = d[5]^(i-1)
> lu = inv(Gu) %*% gu
> 
>  
>  
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 

-- 
Ashton Shortridge
Associate Professor			ashton at msu.edu
Dept of Geography			http://www.msu.edu/~ashton
235 Geography Building		ph (517) 432-3561
Michigan State University		fx (517) 432-1671