[R-sig-Geo] anisotropy gstat

[Dave Depew]

Thanks Edzer,

SO to confirm, the 45 deg direction is the maximum range of correlation, 
or simply just the maximum range to determine the angle of anisotropy?


Edzer Pebesma wrote:
> 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
>