PHP Function to check if a latitude/longitude point is nearer than a distance thresold

DistanceUtils.php

<?php
  /*
	 * Check if the tournament is nearer than the distance thresold
   * according to the latitude and longitude parameters
	 *
	 * param1 : $latitude of the user
	 * param2 : $longitude of the user
	 * param3 : max distance
	 *
	 * Formula : http://www.movable-type.co.uk/scripts/latlong.html
	 */

	public function isNearerThan($latitude, $longitude, $distanceThresold) {

		$earthRadius = 6371;

		$dLat = deg2rad($latitude - $this->latitude);
		$dLon = deg2rad($longitude - $this->longitude);

		$lat1 = deg2rad($this->latitude);
		$lat2 = deg2rad($latitude);

		$a = sin($dLat / 2) * sin($dLat / 2) +
			 sin($dLon / 2) * sin($dLon / 2) * cos($lat1) * cos($lat2);

		$c = 2 * atan2( sqrt($a) , sqrt(1-$a) );

		$distance = $earthRadius * $c;

		return ($distance <= $distanceThresold) ? true : false;
	}
?>