> -----Original Message----- > From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED] On Behalf Of Julian Burgos > Sent: Tuesday, November 08, 2005 10:41 PM > To: r-help@stat.math.ethz.ch > Subject: [R] Variograms and large distances > > 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 > > Hi Julian,
I suggest you transform your coordinates to UTM. I use Eino Uikannen's GeoConv program http://www.kolumbus.fi/eino.uikkanen/geoconvgb/index.htm but i believe there are packages and functions in R to carry out the transformation. GeoConv is a DOS program that runs in batch mode from the DOS console. Ruben ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
