Hello,
  I have multiple observations (replicates) per station...and the stations are distributed in space.
   
  I've applied models using  lme and gls from the nlme library. I've messed around with compound symmetry to capture the correlation within stations. My question is.....I have x and y coordinates for each station (the subsamples have nearly the same coordinates)...how do you include a spatial correlation structure between stations?
   
  I tried things like:
   
  tmp<-gls(y~z,correlation=corSpher(form=~xcoord+ycoord| Station))
   
  but this is modelling the within-station correlation. I want to include between station correlation as some stations are close in space, and others are not. Station is the highest level (it is just 2-way data).
   
  Is this possible? The examples in the literature mainly use xcoord and ycoord as fixed terms.
   
  Kind regards,
  Pieter Bell
   
   
   

 		
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