# Great circle distance matrix

### 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.

### See Also

rdist, exp.earth.cov

### Examples

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
``` |