Re: AI-GEOSTATS: spatial GLMM with nested correlation structure
- John, the gstat R package/S-Plus library, found at
does provide nested variograms, each having their
own anisotropy parameters. However, it does not
do a fully integrated variogram parameter estimation
in a Poisson framework; you'd have to work with
residuals. More specificly, it does not fit anisotropy
ratios nor directions; only sills and ranges.
John Jansen wrote:
>Hello all -- I'm in the midst of modeling the distribution of--
>ice-hauling seals in relation to covariates such as day of year (DOY)
>and ice cover (ICE.COV). By strip-transect sampling on 20 separate
>days, I have created a lattice of cells containing seal counts and the
>corresponding covariate measures. To remove a significant north-south
>trend in seal counts, I extracted the residuals from a GAM loess smooth
>of seal counts on the lat/long variables. Modeling the residuals, I
>arrived at the following S+ best fit (using AIC):
>glmmPQL(sealsum.gamfit ~ ICE.COV * DOY * SHIPACT2, random = ~ 1| DOY,
>family = poisson, data = yakgrid.fit, correlation = corGaus(form = ~
>lat.yak + lon.yak | DOY), verbose = T))
>I determined that a gaussian variogram best fit the spatial
>autocorrelation by exploring the data in Surfer, VarioWin, and S+. But
>I have encountered a significant degree of both geometric and zonal
>anisotropy. I believe the anisotropy is real as there are several
>reasonable hypothesis that explain its presence which have to do with
>the seals concentrating in a stream of ice, i.e., creating
>discontinuities in variance and correlation within the study area.
>Though complicated, I have been able to model the autocorrelation (in
>VarioWin) by nesting two spatial structures (both Gaussian)
>corresponding to the directions of maximum and minimum continuity. The
>problem is that I now need to transport this nested model into the S+
>spatial GLMM framework. The avenues I have explored thus far are:
>1) create a new corStruct class in S+ that corresponds to a
>gaussian-gaussian nested model. Problem: I have been unable to find
>any documentation on how to create a new class though the online help
>indicates that it is possible "by specifying a constructor function and
>methods for the functions corMatrix and coef".
>2) transforming/weighting the coordinates prior to running the model.
>Problem: though a geometric transform of the coordinates is
>straightforward it is less obvious how to conduct such a transform using
>a nested model.
>It may be I'm forcing a square peg (nested model) in a round hole (S+
>spatial GLMM), but I'm hoping someone out there has done this in S+
>before and can pass along their experience. Otherwise, I'm soliciting
>the wisdom of those who know where to find the square hole that matches
>my square peg, i.e., other software or techniques that allow one to
>account for spatial correlation with nested structures with the main
>focus of modeling the relation of animals to their environment. Much
>gratitude to any assistance. Thanks, John Jansen
>John K. Jansen
>National Marine Mammal Laboratory
>7600 Sand Point Way N.E. Bldg 4
>Seattle, WA 98115-6349
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