[R] Variograms and large distances

[Julian Burgos]

Hello R list,
I need to compute empirical variograms using data from a large 
geographic area (~10^6 km2).  Although I could not find a specific 
reference, I assume that both geoR and gstat calculate distances among 
data points assuming points are on a flat surface (using the Pythagorean 
Theorem).  Because the location of my data is large and located near the 
pole, assuming that latitude and longitude are coordinates on a flat 
surface would introduce a -possibly large- bias in the empirical 
variogram estimate.  My questions are the following:

a)  Does geoR and gstat assume that points are on a flat surface?

b) If I first calculate the distances among points using the Haversine 
formula, it is possible to calculate the variogram with a matrix of 
distances among points (where n is the number of observations) and a 
vector of observation values?

Any help would be appreciated.

Julian

Julian M. Burgos

Fisheries Acoustics Research Lab
School of Aquatic and Fishery Science
University of Washington

1122 NE Boat Street
Seattle, WA  98105 

Phone: 206-221-6864