/**
     * @param $lat1
     * @param $lng1
     * @param $lat2
     * @param $lng2
     * @return float 结果以【米】为单位
     */
     function _getDistance($lat1, $lng1, $lat2, $lng2)
    {
        $earthRadius = 6367000; //approximate radius of earth in meters
        $lat1 = ($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 * $stepTwo;
        return round($calculatedDistance);
    }

参考：di  zhi  wang  ji  le