We needed to compute the distance between two points on the Earth using longitude and latitude from Google’s Geocode API service. We use PHP, but there was no reference to a PHP implementation of the Haversine Equation, so I made one. I needed miles, but if you need another unit, just replace $earth_radius with the appropriate value. Enjoy!

public function distance($long_1,$lat_1,$long_2,$lat_2) { $earth_radius = 3963.1676; // in miles $sin_lat = sin(deg2rad($lat_2 - $lat_1) / 2.0); $sin2_lat = $sin_lat * $sin_lat; $sin_long = sin(deg2rad($long_2 - $long_1) / 2.0); $sin2_long = $sin_long * $sin_long; $cos_lat_1 = cos($lat_1); $cos_lat_2 = cos($lat_2); $sqrt = sqrt($sin2_lat + ($cos_lat_1 * $cos_lat_2 * $sin2_long)); $distance = 2.0 * $earth_radius * asin($sqrt); return $distance; }

Hat tip to Aaron Overton for an error in the $sin_long line.