 Dear Sweta J.P.,

The function autofitvariogram does not support fitting anisotropic
variograms. The function does do something however. The example below
illustrates what happens (under the hood automap uses fit.variogram to
fit the variogram):

library(automap)

loadMeuse()

# No anisotropy
vgm1 <- variogram(log(zinc)~1, meuse)
v.noanis = fit.variogram(vgm1, vgm(1,"Sph",300,1))

# Anisotropy
vgm2 <- variogram(log(zinc)~1, meuse, alpha = c(0,45,90,135))
v.anis = fit.variogram(vgm2, vgm(1,"Sph",300,1))

# Removing anisotropy
vgm2$dir.hor = 0
v.removeanis = fit.variogram(vgm2, vgm(1,"Sph",300,1))

v.noanis
v.anis
v.removeanis

'v.anis' and 'v.removeanis' are the same. So fit.variogram ignores the
anisotropy and treats the anisotropic sample variogram as one big
isotropic variogram. So it fits an average isotropic variogram model
from the anisotropic sample variogram. I'll add a warning to the automap
package that tells people that anisotropy is not supported by
autofitVariogram.

However, there is a function in the intamap package which can
automatically detect anisotropy. You can use this function to get the
anisotropy parameters. Then rescale your 2D space to an isotropic 2D
space, use autofitVariogram, make predictions and rescale to the
original anisotropic 2D space. This is what is done in the intamap package.

regards,
Paul

ps I also cc'ed the R-sig-geo mailing list with this e-mail as it might
prove interesting for more users of automap.

On 07/19/2011 07:46 PM, Jinnagara Puttaswamy, Sweta wrote:
>
> Hello Dr. Hiemstra,
>
>  
>
> When I use alpha parameter as a set of angles, eg: alpha
> =c(0,45,90,135), how does the autofitVariogram model this directional
> sample variogram? Will it take the average in all direction and then
> fit a model ?
>
>  
>
> Thank you !
>
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>
> Sweta J.P.
>
> Information Analyst II
>
> Department of Environmental Health
>
> Emory University, Rollins School of Public Health
>
> 1518 Clifton Road NE, Atlanta, GA 30322
>
> (404) 712-8072
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