Calculating distances from latitude and longitude (PHP)

Enter latitude and longitude of two places, and find out the distance between them:

	Latitude	Longitude	// Function takes latitude and longitude // of two places as input and prints the // distance in miles and KMs. function toMiles($lat1, $lon1, $lat2, $lon2) { // Formula for calculating distances // from latitude and longitude. $dist = acos(sin(deg2rad($lat1)) * sin(deg2rad($lat2)) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($lon1 - $lon2))); $dist = rad2deg($dist); $miles = (float) $dist * 69; // To get kilometers, multiply miles by 1.61 $km = (float) $miles * 1.61; // This is all displaying functionality $display = sprintf("%0.2f",$miles).' miles' ; $display .= ' ('.sprintf("%0.2f",$km).' kilometers)' ; return $display ; }
First Place
Second Place

Other references

From CENSUS.GOV: How to calculate distances between 2 points on the earth
http://www.census.gov/cgi-bin/geo/gisfaq?Q5.1
From USGS National Mapping Information: Get geographic information about US based locations:
http://geonames.usgs.gov/pls/gnis/web_query.gnis_web_query_form
Comprehensive lookup for UK addresses
http://www.streetmap.co.uk/
How to determine latitude and longitude given a street address, city, state, province, territory, country or whatever.
http://www.hmssurprise.org/Resources/whereami.html