[R] Variograms and large distances

[Ruben Roa]

> -----Original Message-----
> From:	r-help-bounces at stat.math.ethz.ch [SMTP:r-help-bounces at stat.math.ethz.ch] On Behalf Of Julian Burgos
> Sent:	Tuesday, November 08, 2005 10:41 PM
> To:	r-help at 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