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.