mysql函数-依据经纬度坐标计算距离

class Distance{
const EARTH_RADIUS = 6378.137; // earth radius (const) kilometer

	/**
	 *
	 *	Example:
	 *	$precision = 49;
	 *	ini_set("precision", $precision);
	 *	echo pi(); //will output 3.141592653589793115997963468544185161590576171875
	 *
	 *	1 kilometer = 0.621371192 mile
	 *
	 *	@param double d
	 *	@return double data
	 */
	private function rad( $d )
	{
	return $d * M_PI / 180.0;
	}

	/**
	 *
	 *	Example : get_distance(44.2112,-88.4175,34.5082,-82.6498)
	 *	Get Distance between two point : longitude,latitude(lat1,lng1 => lat2,lng2 )
	 *
	 *	@param double d
	 *	@return double data
	 *
	 */
	public function get_distance( $lat1, $lng1, $lat2, $lng2, $base = 1000 )
	{
	$radLat1 = floatval( $this->rad($lat1) );
	$radLat2 = floatval( $this->rad($lat2) );
	$a = $radLat1 - $radLat2;
	$b = $this->rad($lng1) - $this->rad($lng2);

	$s = 2 * asin(sqrt(pow(sin($a/2),2) + cos($radLat1) * cos($radLat2) * pow(sin($b/2),2)));

	$s = $s * self::EARTH_RADIUS;
	$s = round($s * 10000) / 10000;

	return $s;
	}
}