[R-sig-Geo] What is the reason for Very high value by Universal Kriging based on Nested 3D varigram

[Edzer Pebesma]

You don't describe your problem completely, and you also do not provide
a reproducible example, so I can only make a wild guess: your z variable
takes an extreme value at the prediction location(s) where you see the
high predictions.


On 12/04/2014 08:19 AM, Bingwei Tian wrote:
> Dear list,
> 
> I am doing a 3D estimation of logtransfered subsurface temperature (with a
> strong vertical trend) with a Nested 3D variogram, but the results show very
> high value over than origin data.
> This is not normal and absolutely wrong if I back transfer logged data.
> 
> I attached the 
> <http://r-sig-geo.2731867.n2.nabble.com/file/n7587514/vgm.png>  and anyone
> who knows what is the reason for the very high value differ from origin
> data?
> Or what kind of processing I should to do for the data back transfer? Thanks
> in advance for any help.
> 
> Data:
> summary((spdf$logt))
>           Min.        1st Qu.         Median           Mean        3rd Qu. 
> 0.741937344729 3.487375077900 3.908014984030 3.952886346280 4.452019006490 
>           Max. 
> 5.733988316710 
> 
> Model: Nested 3D varigram
> uk.eye1  <- vgm(psill = 0.155,  model = "Gau",  range=700,  nugget=0)
> uk.eye   <- vgm(psill = 0.125,  model = "Sph",  range=35000,  nugget=0, 
> add.to=uk.eye1)
>   model psill range
> 1   Nug 0.000     0
> 2   Gau 0.155   700
> 3   Nug 0.000     0
> 4   Sph 0.125 35000
> UK: 
> logt.uk <- krige(log(t)~z, spdf, grid, model = uk.eye, nmax = 20)
> 
> Result:
> 
> summary((logt.uk$var1.pred))
>           Min.        1st Qu.         Median           Mean        3rd Qu. 
> -1.66562650678  3.30346488250  3.76836777085  3.81376070431  4.24457939254 
>           Max. 
> 15.05945622140 
> 
> 
> 
> -----
> Bingwei
> 
> Ph.D. Student 
> Kyoto University
> C-1-2-225, Katsura Campus, Kyoto University, 
> Nishikyo-ku, 〒615-8530, Kyoto, Japan
> --
> View this message in context: http://r-sig-geo.2731867.n2.nabble.com/What-is-the-reason-for-Very-high-value-by-Universal-Kriging-based-on-Nested-3D-varigram-tp7587514.html
> Sent from the R-sig-geo mailing list archive at Nabble.com.
> 
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-- 
Edzer Pebesma,  Co-Editor-in-Chief Computers & Geosciences
Institute for Geoinformatics (ifgi), University of Münster
Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795

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