[R-sig-Geo] Cubic variogram models - in vgm( )? elsewhere?

[Edzer Pebesma]

On 01/10/2015 06:02 AM, Ted wrote:
> Hi all -
> 
> Apologies if the answer to this is obvious - it isn't to me so any help appreciated.
> 
> I have been asked to match in R some kriging done in Isatis (BTW, this is not part
> of any assessment task). The model that was used in Isatis was a cubic one. Specifically,
> it is a nested cubic one of the form:
>   
>   Structure 1: Cubic(60', 80') sill = 220
>   Structure 2: Cubic(Inf, 80') sill = 100
> 
> That's probably more information than needed for my question. Basically it is clear that 
> we are dealing with zonal anisotropy (managed by extreme geometric anisotropy). 
> 
> But how do I generate a cubic model in R? I have been using vgm() and although cubic
> models are not commonly used I have this challenge placed before me and wonder what
> I can do in the absence of an explicit "Cub" model  :-)
> 

As you mentioned vgm(), I'll assume you are looking at package gstat in
R, one of the many packages doing geostatistics in R.

You don't specify what the cubic model is. Is it the same as described here:
http://support.sas.com/documentation/cdl/en/statug/63347/HTML/default/viewer.htm#statug_variogram_a0000000579.htm
?

It would be pretty trivial to implement this model in the code behind
vgm(), but hasn't been done; it's the first time I see this model. You
can of course precompute model values and pass these as model "Tab" to
vgm(), (see ?vgm), or you can write your own cubic model R function and
pass that on to gstat::krige0 (which has more limited capabilities than
gstat::krige).

The meaning of your Structure 1 and 2 listed above requires working
knowledge of Isatis - I would recommend to not assume this, and explain
what is meant by them instead.
-- 
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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 490 bytes
Desc: OpenPGP digital signature
URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20150111/6f46ca9a/attachment.bin>