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

[Zev Ross]

Hi Dr. Ribeire, This is very helpful, thank you. I was assuming that my code did split the nugget into measurement error and micro-scale variation when I specified in the krige.control "micro=myfit$nugget/2" is this not correct? This, I thought, splits the nugget in half. I also noticed that when I do this, the kriging variance seems odd with a lot of zeros or very low numbers do you know why? I don't suppose you can direct me to some example code that explains how to compute the measurement error using locations as "blocks" and subtracting from the nugget. I don't see that mentioned in your book (the book is very useful by the way). Zev Paulo Justiniano Ribeiro Jr wrote: 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, _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo -- Zev Ross ZevRoss Spatial Analysis 303 Fairmount Ave Ithaca, NY 14850 607-277-0004 (phone) 866-877-3690 (fax, toll-free) [EMAIL PROTECTED]

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