> I have a bunch of geographic locations specified by lat-long 
> coordinates. What's an easy way to calculate geographic distance 
> between any two points? OR, perhaps there is a function for 
> calculating a distance matrix for K sites? 

A comparison of some geographic distance calculations is provided at 
http://pineda-krch.com/2010/11/23/great-circle-distance-calculations-in-r/ 
, along with code for calculating the Vincenty inverse formula, which 
relies on the WGS-84 ellipsoid approximations.

The author compares the results to fields::rdist.earth, which seems to 
rely on a spherical model of the earth.  It would be interesting to 
compare it to other distance functions as well.

I found that the function provided at the above URL did not handle the 
case of coincident points.  Adding the following line after the while loop 
fixed this.
        if (iterLimit==100) return(0)  # formula began with nearly or 
exactly coincident points

Enjoy the days,
cur
-- 
Curt Seeliger, Data Ranger
Raytheon Information Services - Contractor to ORD
seeliger.c...@epa.gov
541/754-4638

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