The help page for variogram in the spatial package
leaves my slightly uncertain about a few things. I'd
be grateful for confirmation of my understanding.
If I fit a trend surface using surf.ls, and then set
the krig parameter to use that object in the variogram
function, I'm assuming that the variogram produced is
calculated for the residuals contained in the trend
surface object. Is that right?
I'm afraid I don't have the references to check the
following either. Using notation of Cressie, am I
right in thinking that the y co-ordinate of the
variogram corresponds to gamma (or 2x gamma)? And x:
is that h?
And then, how does h correspond to my original data?
i.e. do I interpret it as distance calculated with the
original x and y submitted to surf.ls, or as distance
calculated with the rescaled x and y used within
surf.ls (I understand that the internals rescale x and
y to -1:1).
I'd actually like to check for isotropy before using
this variogram function. Any suggestions as to
functions I might use?
Thanks in advance.
Hywel
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