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

for kriging a preliminary analysis is important. We should know if the data
has trend or how are the ouliers? should we remove them or not. Some of the
kriging techniques like universal kriging create very odd values at some
points if we dont deal with the data frist hand before kriging. I hope that
we can come up with the software that does all this by itselft ( some sort
of decision maker like AI). I hope to see this kind of sotware pretty soon
and I wish it be open source.
  

On Mon, May 25, 2009 at 6:42 PM, Edzer Pebesma <
edzer.pebesma at uni-muenster.de> wrote:

  

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:

require(gstat)
require(geoR)
xyz = data.frame(x = c(0,0,1), y = c(0, 1, 1), z = c(1,2,3))
coordinates(xyz)=~x+y
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)))
kr1
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.
--
Edzer

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 ?crit:
      

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

      
------------------------------------------------------------------------
      

--
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of M?nster
Weseler Stra?e 253, 48151 M?nster, 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