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List:       r-sig-geo
Subject:    [R-sig-Geo] gstat: choice of inverse distance power in idw()
From:       "Mudrak, Erika [EEOBS]" <mudrak () iastate ! edu>
Date:       2010-08-30 16:31:48
Message-ID: 1E7ADA3325202A43BC5B52A5A9A843EF0377B5D54D () EXITS713 ! its ! iastate ! edu
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I used the gstat package to interpolate measurements of eight environmental variables \
in a square 15.4 m x 15.4 m, and then I used model selection from another package to \
build models of dependence of plant population locations on those environmental \
variables.  I used the idw() function to interpolate the environmental variables.  \
The model selection procedure defined which of the eight variables helped to explain \
the patterns seen in my plant populations.

Are there any guidelines for the choice of the inverse distance weighting power \
(idp)?   I had been using idp=2, because it was the default, but for some variables \
it made the surface look not very smooth.   I have tried my models on surfaces with \
other values of idp, and changing this parameter causes the model selection procedure \
to arrive at different models.

Does anyone have any advice or guidelines about the choice of the ipd parameter, \
other than "tweaking" it until the surfaces look smooth?

Thank you,

Erika Mudrak

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