计算地球上两点间的距离

	/**
	* @desc 根据两点间的经纬度计算距离
	* @param float $lat 纬度值
	* @param float $lng 经度值
	*/
	function get_distance($lat1, $lng1, $lat2, $lng2){
		$earthRadius = 6367000; //approximate radius of earth in meters
 
		//Convert these degrees to radians to work with the formula
 
		$lat1 = ($lat1 * pi() ) / 180;
		$lng1 = ($lng1 * pi() ) / 180;
 
		$lat2 = ($lat2 * pi() ) / 180;
		$lng2 = ($lng2 * pi() ) / 180;
 
 
		$calcLongitude = $lng2 - $lng1;
		$calcLatitude = $lat2 - $lat1;
		$stepOne = pow(sin($calcLatitude / 2), 2) + cos($lat1) * cos($lat2) * pow(sin($calcLongitude / 2), 2);
		$stepTwo = 2 * asin(min(1, sqrt($stepOne)));
		$calculatedDistance = $earthRadius * $stepTwo;
		//精确到小数点后两后 
		return round($calculatedDistance,2);
	}