[R-sig-Geo] [Soc] GRASS module for kriging - call for users [was: R-sig-Geo Digest, Vol 69, Issue 21]

Edzer Pebesma edzer.pebesma at uni-muenster.de
Mon May 25 12:42:01 CEST 2009

I believe that many interpolation problems "out there" are simple, and
can be solved using geostatistics with a "finish" or "interpolate"
button. A question I find interesting is whether this button should
always do its best, or should it be so clever to warn the user in case a
problem is not "that simple", and what the criteria are for this.

Of course this SoC project is about an "interpolate" button using open
source software, so the user is always able to find out every detail
behind it. But will she or he actually do this in a non-simple case?

As of your claim that no two geostatistical packages provide the same
result, as a more optimistic person I'd like to provide some
counter-evidence; please run:

xyz = data.frame(x = c(0,0,1), y = c(0, 1, 1), z = c(1,2,3))
x0 = SpatialPoints(data.frame(x=0,y=.5))
kr1 = krige(z~1,xyz,x0,vgm(1, "Exp", 1))
kr2 = krige.conv(as.geodata(xyz), locations=coordinates(x0),
	krige=list(cov.model="exponential", cov.par=c(1,1)))
c(kr2$predict, kr2$krige.var)
kr1[[1]] - kr2$predict
kr1[[2]] - kr2$krige.var

I'd be more than happy if someone could repeat this, or another example,
with ArcGIS or other software, of course.

Ebrahim Jahanshiri wrote:
> Dear Ann,
> I think having a "finish" button is the ulitimate thing that all of us
> looking for in a software!. Unfourtunately it is not possible. There are far
> too many issues regarding a good kriging operation that prevents you from
> trusting a nice package like "Geostatistical Analyst" in ArcGIS. The
> evidence is that you cant find two geostatistical package that their resutl
> is the same (I know this is a big statement but I have seen this for a
> couple of softwares!). I cant say the surface that is generated by ArcGIS is
> not accurate but it bothers me to not know what happens beneath the program
> when it fits the variogram and calculates the matrices for kriging and more
> importantly a "routine" that you mentioned will not work for all the data.
> So personaly I will go for the chors of GeoR or Gstat instead of using the
> ArcGIS. Though it is not complete and I have to admit that I have a lot of
> problem adapting to it.
> Ebrahim
> On Sun, May 24, 2009 at 1:59 AM, Anne Ghisla Insubriae <
> a.ghisla at studenti.uninsubria.it> wrote:
> Ebrahim Jahanshiri a écrit:
>>>> Dear Anne,
> Ebrahim,
>>>> Thanks for the enquiry. I think we should have done this long before. I
>>>> havent done any geostatistics with GRASS but I did alot in ArcGIS and
> also
>>>> in R (variography). I have to tell you that ArcGIS is for those who want
> to
>>>> have a surface only by just clicking on "finish" button trought its
>>>> powerfull interface. That is, it does not provide a good scientific
>>>> backgroud for you to check the procedure. for example how it fitted the
>>>> variogram model or how exactly it does the "validation". That is why the
>>>> "Geostatistical package" objects or classes are not available for the
>>>> programmers to program with (there is a kriging in "Spatial analyst"
> package
>>>> though that its object is programmable and I personally did some with it.
>>>> but it lacks the variogram modeling). I think they are still working on
> it.
>>>> In short I dont recommend ArcGIS for the so called scientific kriging.
> I was afraid of this. Therefore I guess an interface with too many
> mandatory options would be considered overcomplicated.
> There should be as more options as needed for a flexible calculations,
> and also proper defaults to clik on Ok and get an acceptable result.
> What do you think about this solution?
>>>> In
>>>> the other hand R is very powerfull in that it gives you freedom to do
> your
>>>> own style through coding. I worked with "GeoR" pakcage and it is pretty
> nice
>>>> both in terms of variography and kriging. There are other package like
>>>> "Gstat" that I havent worked with but have good qualities. GeoR
> implements
>>>> the so called "model based geostatistics" which is the application of
>>>> bayesian statististics to the geostistics I guess and it is quite new.
> I'm presently having a look at both geoR and gstat, and also the wrapper
> package automap.
> I guess that the first users of the new module would be already familiar
> with R and GRASS, so their feedback about most used functions is very
> important.
>>>> I hope these comments were helpful and please let me know if you need any
>>>> further explanation from me,
> Very helpful, thank you very much!
>>>> Ebrahim
> best regards,
> Anne

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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.springer.com/978-0-387-78170-9 e.pebesma at wwu.de

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