[R-sig-ME] Using corSpher to correct for spatial autocorrelation

[Julie Lee-Yaw]

Hi 
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 example syntax would be something like:
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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