Message-ID: <48501317.20008@uni-muenster.de>
Date: 2008-06-11T18:01:59Z
From: Edzer Pebesma
Subject: anisotropy gstat
In-Reply-To: <48500CD7.8060700@scimail.uwaterloo.ca>
Dave Depew wrote:
> Hi All,
> I suppose this is a rather simple question...however, I'm managing to
> get more confused the more I read.
> I'm doing some OK and UK using the R-gstat package...I have some data
> that is moderately anisotropic. Reading the gstat literature, it would
> seem that to specify the appropriate parameters for anisotropic
> variograms I need the set the angle equal to the direction of maximal
> data continuity? or maximal range?. The ratio of the minimum to
> maximum range appears to be straightforward enough, but the first part
> is confusing me.
> As an example;
> data(meuse)
> e<-variogram(dist~1, loc=~x+y,data=meuse, alpha=c(0,45,90,135))
> plot(e)
Dave, try
require(gstat)
data(meuse)
coordinates(meuse) = ~x+y
e<-variogram(dist~1, meuse, alpha=c(0,45,90,135))
plot(e, vgm(.08, "Sph", 5000, anis=c(45, .2)))
I got there with a bit of trial and error. Clearly, for the 45 degrees
most happens beyond 1500 m.
Of course this is just for the idea; a variogram model that has some
parabolic behaviour at the origin would be prefered.
>
> Looks to me anyways, that the direction of maximum range is 45 deg,
> and the minRange/maxRange is ~ 1000/1500 = 0.67.
the max correlation direction is 45, the range is, in my model, 5000,
the anisotropy ratio 0.2.
>
> Could more experienced gstat users tell me if I'm out to lunch on this
> one??
You weren't far off.
--
Edzer