[R-sig-Geo] anisotropy modeling

[Edzer Pebesma]

help(fit.variogram) has the following description:

     Fit ranges and/or sills from a simple or nested variogram model to
     a sample variogram

I suspected it would completely ignore anisotropy settings. However,
this seems not to be the case:

> library(gstat)
Loading required package: sp
Loading required package: spacetime
Loading required package: zoo
Loading required package: xts
> loadMeuse()
> v0 = variogram(zinc~1,meuse, alpha = 0, tol.hor = 45)
> v90 = variogram(zinc~1,meuse, alpha = 90, tol.hor = 45)
> v = variogram(zinc~1,meuse)
> fit.variogram(v, vgm(1, "Exp", 300, anis=c(90,1)))
  model  psill    range
1   Exp 166238 323.6674
> fit.variogram(v, vgm(1, "Exp", 300, anis=c(90,.1)))
  model  psill    range ang1 anis1
1   Exp 166238 3236.674   90   0.1
> fit.variogram(v0, vgm(1, "Exp", 300, anis=c(90,.1)))
  model    psill    range ang1 anis1
1   Exp 146068.7 2772.751   90   0.1
> fit.variogram(v90, vgm(1, "Exp", 300, anis=c(90,.1)))
  model    psill    range ang1 anis1
1   Exp 200767.2 4027.282   90   0.1
>


On 07/13/2011 11:34 AM, Matevž Pavlič wrote:
> Hi, 
> 
> thanks for the reply. Can you explain this a little bit more :
> " it assumes the variogram to fit to is in the major (correlation) direction (or averaged over all directions)."
> 
> I don't know exactly ehat it means....
> m
> 
> -----Original Message-----
> From: r-sig-geo-bounces at r-project.org [mailto:r-sig-geo-bounces at r-project.org] On Behalf Of Edzer Pebesma
> Sent: Wednesday, July 13, 2011 10:10 AM
> To: r-sig-geo at r-project.org
> Subject: Re: [R-sig-Geo] anisotropy modeling
> 
> 
> 
> On 07/12/2011 10:52 PM, Matevž Pavlič wrote:
>> Hi all,
>>
>>  
>>
>> i 'm am not entirely sure I understand anisotropy kriging in R. 
>>
>> I have a data set in which is (at least i think so) anisotropy is clearly visible. So I made directional variograms....
>>
>> So as i understand, the only thing that is different from >normal< kriging is the  >anis< property in which you define the diffrenece of ranges? Is that coreect?
> 
> Yes. Please note that fit.variogram ignores anything about anisotropy, it assumes the variogram to fit to is in the major (correlation) direction (or averaged over all directions).
> 
>>
>> Bellow is the code i use :
>>
>>  
>>
>> a<-5000/7000
>>
>> print(plot(variogram(Z ~ 1, DF, map = TRUE, cutoff = 15000, width = 
>> 100), main = "Variogram map, podlaga",col.regions = 
>> terrain.colors(64)))
>>
>> v1.a<-variogram(Z~1, DF, alpha=c(45, 135))
>>
>> (vmf.a <- fit.variogram(v1.a, vgm(2900, "Pen", 5500, 300, anis = 
>> c(135, a))))
>>
>> print(plot(v1.a, pl = F, pch = 20, col = "blue"))
>>
>> print(plot(v1.a, plot.numbers = F, pch = 20, col = "darkblue", model = 
>> vmf.a))
>>
>>  
>>
>> podlaga.aniso<-krige(Z~1, DF[-zerodist(DF)[,1],], grd, vmf.a )
>>
>> print(spplot(podlaga.aniso, zcol="var1.pred", 
>> col.regions=terrain.colors(64), contour=T, pretty=T, cuts=15, 
>> key.space="right"))
>>
>> print(spplot(podlaga.aniso,  zcol="var1.var", 
>> col.regions=terrain.colors(64), contour=T, pretty=T, cuts=15, 
>> key.space="right"))
>>
>> writeGDAL(podlaga.aniso, "podlaga_aniso.tif")
>>
>>  
>>
>> thanks for info,
>>
>>  
>>
>> m
>>
>>
>> 	[[alternative HTML version deleted]]
>>
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> 
> --
> Edzer Pebesma
> Institute for Geoinformatics (ifgi), University of Münster Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
> http://www.52north.org/geostatistics      e.pebesma at wwu.de
> 
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de