[R-sig-Geo] GSTAT and anisotropy

[Michael Hewson]

I would like an opinion please on package gstat and examining anisotropy in variograms.

I have a set of atmospheric science variables in a regular grid of 3000 points at 1 km resolution.


When I use this code for one variable:



plot(variogram(d1$wrfae ~ 1, d1, alpha=c(0, 45, 90, 135)))

I can see the four different directions have different experimental variograms thus exhibiting anisotropy for that variable (as one might expect in an atmospheric data set). I can do the same for another variable of course.

I construct a cross-variogram for two of the variables and plot for anisotropy thus (because this is what I want - the cross-variogram examining spatial correlation):

g <- gstat(NULL, id = "ae", form = wrfae ~ 1, data=d1)
g <- gstat(g, id = "in", form = intensity ~ 1, data=d1)
xv1.aeVin <- variogram(g, alpha=c(0))
xv2.aeVin <- variogram(g, alpha=c(45))
xv3.aeVin <- variogram(g, alpha=c(90))
xv4.aeVin <- variogram(g, alpha=c(135))
plot(xv1.aeVin)
plot(xv2.aeVin)
plot(xv3.aeVin)
plot(xv4.aeVin)

but - I get exactly the same experimental variograms for two variables - and the cross-variogram - for each direction (thus implying isotropy).

If I use:
g <- gstat(NULL, id = "ae", form = wrfae ~ 1, data=d1)
g <- gstat(g, id = "in", form = intensity ~ 1, data=d1)
xv.aeVin <- variogram(g, alpha=c(0, 45, 90, 135))

then I can see the anisotropy for the larger varying variable variogram - but the now superimposed graphs contain also the small varying variable variogram - and the cross-variogram - these lines are not distinguishable from the x-axis in the four plots (thus unreadable for analysis).

I'm looking for a single plot set (2 variograms and a cross variogram for a given direction) - can I achieve that with some code amendments to my second set of code above?

Alternatively - can I extent the y axis (semi-variance) in the third set of code above?

If it helps I can add the plots ...

My thanks,
________________________________________________________
Michael Hewson PhD candidate
Climate Research Group<http://www.gpem.uq.edu.au/crg> | Centre for Spatial Environmental Research<http://www.gpem.uq.edu.au/cser>
The University of Queensland | Brisbane Q 4072 | Australia
m.hewson at uq.edu.au | +61 (0)408 379 373

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