[R-sig-Geo] Note on variogram fitting with polynomial degree

[Caspar Hallmann]

Hi Edzer,
Thanks for the clarification. Well, ideally, I think variogram()
should be made possible to account for "degree". Alternatively a
simple note in the help file for variogram along the lines "NOTE:
degree is not used in variogram(), Use formula to specify a trend
surface instead", might suffice.
Thanks again
Caspar


On Tue, Sep 17, 2013 at 12:27 PM, Edzer Pebesma
<edzer.pebesma at uni-muenster.de> wrote:
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> degree is not listed as a parameter in ?variogram, and is ignored,
> regrettably silently, but this is how R often works when there's a ...
> in the argument list.
>
> The function that accepts degree is ?gstat, and I tried:
>
> variogram(gstat(NULL, "lzinc", log(zinc)~1, meuse, degree=2))
>
> and that gives a nice error message that degree is not supported by
> variogram().
>
> I understand this is somewhat confusing. Do you think we should modify
> the book or the documentation of some function?
>
> On 09/17/2013 11:36 AM, Caspar Hallmann wrote:
>> Dear all,
>>
>> I read in ASDAR: "Residual variograms are calculated by default
>> when a more complex model for the trend is used..."
>>
>> However, I noticed that when using fit.variogram in gstat with an
>> additional option: degree=2, but keeping the formula as an
>> intercept only, does not account for the higher degree of
>> complexity in the model. I suspect this is not the intended
>> behavior. To honour a dependence structure (polyn degree) in my
>> observations I need to state the dependence explicitly in the
>> formula.
>>
>> Best regards,
>>
>> Caspar
>>
>> data(meuse) coordinates(meuse) <- c("x", "y")
>> v<-variogram(log(zinc)~1,meuse) print(v)
>> vs<-variogram(log(zinc)~1,meuse,degree=2) print(vs)
>> vt<-variogram(log(zinc)~x*y+I(x^2)+I(y^2),meuse) print(vt)
>>
>> PS: x86_64-w64-mingw32/x64 (64-bit) R version 3.0.1 (2013-05-16)
>> gstat_1.0-16
>>
>> _______________________________________________ R-sig-Geo mailing
>> list R-sig-Geo at r-project.org
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>
> - --
> Edzer Pebesma
> Institute for Geoinformatics (ifgi), University of Münster
> Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
> 83 33081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de
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