On Friday, December 7, 2001, at 10:05 AM, Andreas Hartmann wrote:
>
> How do I compute the residual semivariogramm when I don't know the
> residuals? Or have I misunderstood something in the concept of external
> drift?
There is a nice section (Chapter 5.4) in Cressie's textbook (Statistics
for
Spatial Data) that discusses the potential bias of estimating
semivariograms from residuals and Matheron's formulation of
IRF-K kriging as an alternative means to krige in the presence of
a trend. The iterative fitting of the covariance is usually
non-graphical,
which is a drawback in itself, and Fig. 5.1 in the same section shows
Cressie's bold attempt at showing the pitfalls of doing such an
"automatic" fit. I have not used IRF-K kriging very much in practice,
for the above reasons. Better to live with the devil that I know, i.e.
my -- albeit biased -- residual variogram.
Regards,
Syed
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