R help - Jun 2012 - Specifying spatial correlation Form in nmle

Dear R users,

I'm applying a correlation structure in a mixed model (nmle function) to
control for spatial correlation between land parcels that are adjacent to
each other. I generated X,Y coordinates in ArcGIS for each land parcel and
used them in the correlation form like this:

test.exp<-corExp(1, form = ~ X + Y)

test.exp<- Initialize(test.exp,dataset)

However, the correlation Matrix generated does not look right. Here is a
portion of the matrix, in which all correlations are 0:
> corMatrix(pdxspc.exp)[1:5, 1:5]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    0    0    0
[2,]    0    1    0    0    0
[3,]    0    0    1    0    0
[4,]    0    0    0    1    0
[5,]    0    0    0    0    1

It seems I'm not using the X Y coordinates correctly in the form. I saw two
examples that used "east" and "north" in their form. But I
do not quite
know what "east" and "north" are. Any help would be greatly
appreciated.

Best
Gary

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