assorted questions

[zij@ornl.gov (Yetta Jager)]

Hello,

This is our first posting to the Gstat list.  We've settled
on using GSTAT to generate indicator simulations of categorical
landcover data.  Our project has the goal of evaluating the
effects of spatial uncertainty on predictions made by ecological
population viability models for endangered species.  The models
depend on spatial data to describe habitat suitability.

We have benefitted greatly from Dr. Pebesma's generosity in 
providing his software and support, but thought it would be
better to use the listserver to give everyone access to the
answers in case others have the same questions.  Here goes:

1. This is a statistical question.  We are using truly categorical
data and I'm not clear whether constructing semivariograms for
cumulative thresholds is correct (order=4).  It seems to me that we want
to avoid having mis-classified locations tend to be in a category 
with an adjacent index.  We found a place in the code where the
inequality could be replaced with an equality, but we don't know if
there are other implications of such a change.

2. We are also interested in cross-validating and tried Xvalid=1.  We're
not sure what the output is.  It gave an additional predicted indicator
variable that seems to correspond to the first category.  We were kind of
hoping for a summary of mean square errors and average kriging variance for
each category predicted one at a time.  Is this already available or should we
write a program to read the original data and kriged probabilities to
do the comparison?

3. Apparently the program doesn't like being asked to predict at a location
exactly matched by one in the input mask.  Is there a switch to set that will
handle this situation?

Thanks for your help,  

Yetta


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Yetta Jager                                             
Environmental Sciences Division   
Oak Ridge National Laboratory         
P.O. Box 2008, MS 6036             
Oak Ridge, TN  37831-6036          
OFFICE: 423/574-8143
FAX:    423/576-8543 
Work email: jagerhi@ornl.gov 
Home email: hjager@utk.edu
WEBpage: http://www.esd.ornl.gov/~zij/
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"One man's mean is another man's Poisson" J.W. Haeffner