haversine formule php / mysql

niet zeker maar :

$R = 6371; // radius of Earth in KM

$lat = '46.98025235521883'; // lat of center point
$lon = '-110.390625'; // longitude of center point
$distance = 1000; // radius in KM of the circle drawn 
$rad = $distance / $R; // angular radius for query 
$query = '';

// rough cut to exclude results that aren't close
$radR = rad2deg($rad/$R);
$max_lat = $lat + radR;
$min_lat = $lat - radR;
$radR = rad2deg($rad/$R/cos(deg2rad($lat)));
$max_lon = $lon + radR;
$min_lon = $lon - radR;
// this part works just fine!
$query .= '(latitude > ' . $min_lat . ' AND latitude < ' . $max_lat . ')';
$query .= ' AND (longitude > ' . $min_lon . ' AND longitude < ' . $max_lon . ')';
// refining query -- this part returns no results
$query .= ' AND acos(sin('.deg2rad($lat).') * sin(radians(latitude)) + cos('.deg2rad($lat).') * cos(radians(latitude)) *
    cos(radians(longitude) - ('.deg2rad($lon).'))) <= '.$rad;