Dear Edzer

Thank you greatly for your reply. I have attempted to implement the
solution you suggested, but either it's not what I was looking for, or more
likely, I'm missing something. Currently the relevant code passage looks
like this:

##--------------------

m.grid=data.frame(x=outgrid$V1,y=outgrid$V2)
 m_preca=data.frame(x=prec[,2],y=prec[,3],preca=prec[,5])
m_precb=data.frame(x=conc[,2],y=conc[,3],precb=conc[,6])
m_conc=data.frame(x=conc[,2],y=conc[,3],conc=conc[,5])
 coordinates(m.grid) = ~x+y
coordinates(m_preca)=~x+y
coordinates(m_precb)=~x+y
coordinates(m_conc)=~x+y

## Gstat
m.g=gstat(id="conc",formula=conc ~ 1, data = m_conc,
nmax=16,model=vgm(0.4,"Pow",1,add.to=vgm(120,"Sph",200,10)))
m.g=gstat(m.g,id="preca",formula=preca ~ 1,
data=m_preca,nmax=16,model=vgm(0.1,"Pow",1,add.to=vgm(25,"Sph",200,80)))
m.g=gstat(m.g,id="precb",formula=precb ~ 1,
data=m_precb,nmax=16,model=vgm(0.1,"Pow",1,add.to
=vgm(25,"Sph",200,80)),merge=list(c("preca",1,"precb",1)))
m.g=gstat(m.g,id=c("conc","preca"),model=vgm(0.01,"Pow",1,add.to
=vgm(110,"Sph",200,70)))
m.g=gstat(m.g,id=c("preca","precb"),model=vgm(0.01,"Pow",1,add.to
=vgm(110,"Sph",200,70)))
m.g=gstat(m.g,id=c("conc","precb"),model=vgm(0.01,"Pow",1,add.to
=vgm(110,"Sph",200,70)))

## Empirical Variogram
m.g.var=variogram(m.g,width=110,cutoff=600,pseudo=-1)
 ## Fitting
m.g.fit=fit.lmc(m.g.var,m.g,fit.lmc=TRUE,fit.ranges=FALSE,correct.diagonal=1.01,fit.method=7)

## Force same variograms for preca and precb
m.g.fit$model$preca=m.g.fit$model$preca.precb
m.g.fit$model$precb=m.g.fit$model$preca.precb

## Co-Kriging
m.g.fit$set=list(nocheck=1)
m.g.pred=predict(m.g.fit,newdata=m.grid)

##----------------------------

As you can see from the variable names, this has organically grown from
something inspired by the 'meuse' example in gstat.
Here's what I think I'm doing:

- set up a three variable gstat object, where two variables (conc and
precb) come from the same measuring stations. preca comes from another
station network, as discribed in my first message.
- fit variograms and cross-variograms to this object
- force the variograms for 'preca' and 'precb' and their cross-variogram to
be identical
- use the variograms for co-kriging

Am I making some fundamental mistake?

Best Regards
Ralph

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