[R-sig-Geo] Non-symmetric variogram map in gstat

[David Rossiter]

Edzer Pebesma wrote:

> David, you may also notice that the map produced does not have a cell 
> centre or cell 'crossing' at (0,0). Of course you'd assume enough 
> cleverness that this would be enforced automatically, but too bad. Try
>
> v <- variogram(Ni ~ 1, jura.pred, cutoff=1.8, width=0.18, map=T)
>
> (making sure that the cutoff is a multiple of the width) and you'll
see 
> something symmetric.

Edzer,

Thanks for the quick response. That was pretty stupid of me, not
noticing that there was a discrepency in the parameters. I should have
considered something like that; the different dataset should not affect
the algorithm!

Indeed looking at v$map at coords[92,] in my example I see 0.06  0.06; this
is the closest to (0,0). If I try an even multiple:

v <- variogram(Ni ~ 1, jura.pred, cutoff=0.9, width=0.18, map=T)

I get one of the cells as [61,] -2.77556e-17 -8.32667e-17

which I guess is (0, 0) for all practical purposes!

Thanks again,

D G Rossiter
http://www.itc.nl/personal/rossiter