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

[Anne Ghisla]

Edzer Pebesma escribió:
> 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.

Hello Edzer and others that follow this thread,

as suggested by Ebrahim, most users would appreciate a tool able to
quietly fit the analysis to the data oddities, but surely I wouldn't
implement nor use a tool that automagically gives acceptable results
without tracking of the optimisation steps. I have some experience with
ArcView's Animal Movement[0]: I tested the tool in edge cases, where
algorithms *have to* crash, and it always succeeded without
explanations. 
Sincerely speaking, I'm not able to provide such intelligence to my
module in the near future. If we plan to add this functionality later, I
guess it will be good both to log the procedure and/or let user interact
and understand what it is happening in any moment.

Apropos of warning users about possibile difficulties, I think that the
cleverness needed to give such advices is quite hard to implement, but
not impossible. (/me thinks of strategy-missing hints in card games...).

> 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?

I suppose the users to know what they're doing - R and GRASS users are
already aware that the tools they use can give meaningless answers and
it's up to them to use commands consciously. If users want to use
v.autokrige2 just to try it out, they will get the result of a standard
procedure. To obtain something better, they should know how to use the
'advanced' options.

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

Marked on the todo list, stay in touch :)

thank you very much,
Anne

[0] http://www.absc.usgs.gov/glba/gistools/animal_mvmt.htm

> 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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