# rdist.earth: Great circle distance matrix In spectralGP: Approximate Gaussian Processes Using the Fourier Basis

## Description

Given two sets of longitude/latitude locations computes the Great circle (geogrpahic) distance matrix among all pairings. This function and help file are copied from the fields library.

## Usage

 `1` ```rdist.earth(loc1, loc2, miles = TRUE, R = NULL) ```

## Arguments

 `loc1` Matrix of first set of lon/lat coordinates first column is the longitudes and second is the latitudes. `loc2` Matrix of second set of lon/lat coordinates first column is the longitudes and second is the latitudes. If missing x1 is used. `miles` If true distances are in statute miles if false distances in kilometers. `R` Radius to use for sphere to find spherical distances. If NULL the radius is either in miles or kilometers depending on the values of the miles argument. If R=1 then distances are of course in radians.

## Details

Surprisingly this all done efficiently in S.

## Value

The great circle distance matrix if nrow(x1)=m and nrow( x2)=n then the returned matrix will be mXn.

 ```1 2 3``` ``` lon.lat=cbind(runif(20,0,360),runif(20,-90,90)) out<- rdist.earth (lon.lat) #out is a 20X20 distance matrix ```