[SOLVED]Drift Description for Kriging

Any question regarding the Interpolation method using Kriging

[SOLVED]Drift Description for Kriging

Postby Costu » Sat Oct 10, 2015 9:53 am

Hi,

I would like to know how one describes a drift ( e.g., a second order polynomial drift in a 2-D space) through the parameter uc= of the functions vario.calc() and kriging(). I note that the command uc.names() specified in the documentation does not exist in the package.

Thanks,

Francky

Edit moderation: I move this post in the kriging section.
Costu
 
Posts: 10
Joined: Sun Oct 14, 2012 8:37 pm

Re: Drift Description for Kriging

Postby Nicolas Desassis » Sat Oct 10, 2015 12:47 pm

Dear Francky,

here is a short script using a data set of RGeostats to explain how to perform universal kriging.

Load the data:

Code: Select all
data(Exdemo_ext.data)
dat=Exdemo_ext.data #to do shorter


Perform the variography and the modeling:

Code: Select all
vario=vario.calc(dat)
model1=model.auto(vario,struct=c("K-Bessel","Nugget Effect"))


Create the output grid and the neighborhood (unique):

Code: Select all
grid=db.create(nx=c(200,200))
unique=neigh.init(type=0)


Perform ordinary kriging:

Code: Select all
grid=kriging(dat,grid,neigh=unique,model=model1)
plot(grid,pos.legend=1,zlim=c(-4,5))
plot(dat,add=T)


Perform universal kriging with a second order polynomial drift:

Code: Select all
x11()
grid=kriging(dat,grid,neigh=unique,model=model1,uc=c("1","x","y","xy","x2","y2"))
plot(grid,pos.legend=1,zlim=c(-4,5))
plot(dat,add=T)


It seems that there is not a great difference (it is probably due to the
fact that drift is useless in this specific case and the data control the result.
However we can see some differences far from the data points:

Code: Select all
grid=db.add(grid,grid[,6]-grid[,4],loctype="z")
plot(grid,pos.legend=1)
plot(dat,add=T)


I hope it helped you.
I am not really aware about universal kriging :oops:

Regards,
Nicolas
Nicolas Desassis
 
Posts: 198
Joined: Thu Sep 20, 2012 4:22 pm

Re: Drift Description for Kriging

Postby Costu » Sat Oct 10, 2015 1:10 pm

Dear Nicolas,

Thank you so much,

Regards,

Francky
Costu
 
Posts: 10
Joined: Sun Oct 14, 2012 8:37 pm


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