private function fixTimeForGranularity($points, $granularity) {
        if ($granularity != $this->mapper::GRANULARITY_DAILY) {
            return $points;
        }
        foreach ($points as &$value) {
            $date = substr($value['time'],0, 10); // get date (2017-08-29)
            $offset = substr($value['time'], -6); // get timezone offset (+02:00, -04:00)
            $value['time'] = $date . "T00:00:00" . $offset;
        }
        return $points;
    }