[R-sig-Geo] geoR nugget and coincident locations

[Paulo Justiniano Ribeiro Jr]

Dear Zev

The warning is really just a warning and not an error...

the point is you may need some data manipulation in order to run the
analysis you anty.

Firts of all the fact you have duplicated information in (some) locations
may give you the opportunity to split you negget parameter estimate in
measurement error and micro-scale variation.
One possibility to compute the former using the duplicated data (locations
as "blocks" and subtract this from the nugget. The difference givesyouy
the latter.
You can them use thei information when kriging with krige.conv()

hope this helps, otherwise contact me again for further details

best


Paulo Justiniano Ribeiro Jr
LEG (Laboratório de Estatística e Geoinformação)
Universidade Federal do Paraná
Caixa Postal 19.081
CEP 81.531-990
Curitiba, PR  -  Brasil
Tel: (+55) 41 3361 3573
Fax: (+55) 41 3361 3141
e-mail: paulojus AT  ufpr  br
http://www.leg.ufpr.br/~paulojus

On Tue, 30 Oct 2007, Zev Ross wrote:

> Hi All,
>
> At many monitoring locations we've taken two air quality samples. Rather than
> simply average these values, I want to krige all the observations and
> accommodate the different values at coincident locations by including
> measurement error in the nugget.
>
> When I run the code based on geoR, though, I get an error that the coincident
> locations may "cause crashes in some matrices operations" and I'm wondering if
> someone could shed light on the issue -- is this what you'd expect with
> coincident locations? Is the code below incorrectly specified?
>
> Thank you, Zev
>
> # ----set up the modelling and validation samples as geodata
>
> model.a<-as.geodata(samples.hull, coords.col=c("x", "y"),
> 	data.col="no2.ppb",
> 	covar.col=c("phase", "traffic)  )
>
> validation.a<-as.geodata(samples.val, coords.col=c("x", "y"),
> 	data.col="no2.ppb",
> 	covar.col=c("phase", "traffic) )
>
> #-----use the modeling samples to estimate the variogram
>
> myvario<-variog(model.a, option="bin",
> 	breaks=seq(1,10000, by=300), maxdist=10000,
> 	trend=~phase+traffic)
>
> #----- fit the variogram
>
> myfit<-variofit(myvario, ini.cov.pars=c(15, 1000),
> 	cov.model="spherical")
>
> #----- set kriging to include a trend AND split
> #----- the nugget into micro and measurement
>
> KC<-krige.control(type="ok", obj.model=myfit, micro=myfit$nugget/2,
> 	trend.d=trend.spatial(~phase+traffic, model.a),
> 	trend.l=trend.spatial(~phase+traffic, validation.a))
>
> # ----krige
> mykrige<-krige.conv(model.a,locations=validation.a$coords,
> 	krige=KC, output=output.control(signal=F)
>
> # here is the warning
>
> krige.conv: model with covariates matrix provided by the user
> krige.conv: Kriging performed using global neighbourhood
> Warning message:
> Two or more pairs of data at coincident (or very close) locations.
> This may cause crashes in some matrices operations.
>  in: varcov.spatial(coords = coords, cov.model = cov.model, kappa = kappa,
>
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