-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch
[mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of
Nicholas Lewin-Koh
Sent: zondag 12 november 2006 4:23
To: Carlos A. Bastos M.Guerra
Cc: r-sig-geo at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] how to do a principle component
analysis with geo-referenced points
Hi Carlos,
I think that there are tools in the sp package for dealing with grids.
If I am understanding you correctly and you want to do
"zoning" of your region than you probably are not looking to
do pca, but some sort of clustering.
Marie Jose Fortin had some nice papers on a technique called
wombling, for finding regions of abrupt ecological change.
There are some other techniques for spatial partitioning, but
I am not sure if they are implemented in R. It has been a
long time since I worked on ecological problems.
For more information on the spatial tools in R a good place
to start is http://cran.r-project.org/src/contrib/Views/Spatial.html
the CRAN task view for spatial statistics, and
http://cran.r-project.org/src/contrib/Views/Environmetrics.html
has some more pointers.
Hope this helps,
Nicholas
On Sat, 11 Nov 2006 20:24:59 -0000, "Carlos A. Bastos M.Guerra"
<carlosguerra at esa.ipvc.pt> said:
Dear Nicholas,
First of all thanks for the references, I think they will
my current problem. :) The thing is that I am used to work
to do the spatial analysis, but the statistical methods in
a bit "dummy", namely in spatial PCA. I am used to work with R with
the ade4 package :) but when I heard that I could do
with R I ad to try it...but its more difficult that it seams (at
first)...
What I did was: (in ArcGIS) convert the centroids of a grid into a
point shape file, than I have integrated all the information into
different columns. I converted the dbf file into a txt an then I
imported the file into R ... and my problems began... :)
My objective is to do a PCA and extract the different
in order to make an ecological zoning.
I am still starting with R and "the Geo tools" can you
reading material that I can use?
Best regards,
Carlos
-----Mensagem original-----
De: Nicholas Lewin-Koh [mailto:nikko at hailmail.net]
Enviada: s?bado, 11 de Novembro de 2006 19:06
Para: r-sig-geo at stat.math.ethz.ch
Cc: Carlos GUERRA
Assunto: [R-sig-Geo] RE: how to do a principle component
geo-referenced points
Hi Carlos,
There are a couple of ways to do this, but you have to be a little
more specific about what your goals/intentions are. I
points p(x1,y1), ...., p(xn,yn), where p is a vector of
If the goal is interpolation than you have to model the spatial
covariance of the orthognal factors, and you should look at
waekernagel's book.
if your goal is to extract principal components and account for the
variance induced by a spatial process, a quick and dirty
to include polynomials of the xy coordinates in the data
the augmented matrix. Take a look at
Borcard, D., P. Legendre & P. Drapeau. 1992. Partialling out the
spatial component of ecological variation. Ecology 73: 1045-1055
M?ot, A., P. Legendre & D. Borcard. 1998. Partialling out
component of ecological variation: questions and
linear modeling framework. Environmental and Ecological Statistics 5
(1): 1-27.
Another approach is spatial factor analysis
Christensen, WF, and Amemiya, Y (2001). "Generalized
analysis method for multivariate geo-referenced data," Mathematical
Geology, 33, 801-824.
Christensen, WF, and Amemiya, Y (2002). "Latent variable
multivariate spatial data," Journal of the American Statistical
Association, 97, 302-317
If your question is there R code to do this, I think the
can to the spatial variance partitioning, but for factor
are on your own.
Nicholas