[R-sig-Geo] Need help understanding the spatial correlation structure applied in lme

[Ing. Agr. Agustín Alesso]

Dear Arnaud,

First at all, I'm not an expert but your question maybe help me, so my
apologies about that. 
The plot you posted is from Normalised residuals of a fitted lme.object
that already take account for correlation?
Can you submit your code for that plot?

Regards,


Agustin

El mar, 22-02-2011 a las 12:00 +0100, r-sig-geo-request at r-project.org
escribió:
> Dear Users,
> 
> I apologize to resubmit this question to your brains, but I need to
> understand some of my results to be sure that I did not make errors
> setting
> my analysis.
> So, even (and particularly) if the answer is "You are totally wrong",
> please
> let me know !
> 
> >From previous analysis (semi-variograms using package gstat), I found
> spatial autocorrelation in my dataset.
> The best fitted model to this spatial correlation structure is the
> Gaussian
> model (Spherical, Exponential, Linear tested and comparison done by
> Sum of
> Square errors).
> So I used corGaus function to define this spatial autocorrelation in
> my lme
> model using the option "correlation".
> 
> Example: lme( Y ~ X1 + X2 + ... + X3,  random = ~ 1 | RandomFactor,
> correlation = corGaus(form = ~ X + Y | RandomFactor )
> 
> The Variogram function (package nlme) used on a lme object calculates
> the
> semi-variogram for the within-group residuals and add the
> semi-variogram of
> the corSpatial element (corGaus in my case) included in my model ...
> so far
> no problem.
> 
> I was surprised, however, to see on the plot of the semi-variogram
> issued
> from the Variogram function, (see figure at http://imm.io/3OLe) the
> low
> range value (~1600 meters) used in the corGaus structure included in
> the lme
> object.
> When I fitted the same corGaus structure manually or using the
> fit.variogram
> function (package gstat) on the data of each group defined in lme, it
> gaves
> me ranges between 2050 and 2700 meters (mean 2350 meters).
> 
> Can anyone explain me those differences ?
> 
> Note: As I mentioned in a previous message (
> http://markmail.org/message/gjgag4ohjopevgax), I tried to define a
> different
> range in the corGaus function directly in the lme function, but it is
> not
> taken into account.
> 
> Arnaud
> 
>         [[alternative HTML version deleted]]
> 
> 
> 
> ------------------------------ 
-- 
Ing. Agr. Agustín Alesso
Dpto. de Ciencias del Ambiente
Fac. Ciencias Agrarias - UNL
Kreder 2805 - S3080HOF - Esperanza
Tel: 03496-426400 ext 256