[R-sig-Geo] Question about correcting for spatial autocorrelation

[Roger Bivand]

On Fri, 22 Jun 2018, Julie Lee-Yaw via R-sig-Geo wrote:

> Hi 
> I've posted this to the mixed models forum as well but thought people 
> here might know:
> I want to use the the correlation setting with corSpher in nlme to 
> account for potential spatial autocorrelation in my data. My data 
> include observations from across the globe with locations in latitude 
> and longitude (decimal degrees). From the R help for corSpher, the 
> syntax for their wheat example would be something like:

Nothing in the documentation nor the underlying book suggests that the 
coordinates are anything other than planar, so geographical coordinates in 
decimal degrees should not be used. Unfortunately, I do not have access to 
the underlying article in crop science, but there is no reason to think 
that the agricultural experiment extended from France to Turkey and France 
to south of Ghana. The documentation in nlme::corSpher() refers to 
stats::dist, and I can't see any way to insert fields::rdist.earth() in 
its place. So you can safely accept that the coefficients must be 
projected (i.e. planar). This is all accessible in the documentation and 
Pinheiro & Bates (2000). It is pretty certain that they did not envisage 
global scope in geographical coordinates, so maybe you should be using 
fields or gstat which are more likely to be able to handle Great Circle 
distances.

Hope this clarifies,

Roger

> fm1Wheat2 <- gls(yield ~ variety - 1, corr =corSpher(c(28, 0.2), form = 
> + ~ latitude + longitude, nugget = TRUE))
>
> My question is whether the latitude and longitude provided should be 
> projected into a spatial projection that preserves distances or areas or 
> whether providing decimal degrees is appropriate?

> Many thanks!

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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand using nhh.no
http://orcid.org/0000-0003-2392-6140
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