[R] Variograms and large distances
Julian Burgos
jmburgos at u.washington.edu
Wed Nov 9 01:40:42 CET 2005
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
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