protected function prepareIndex($index)
    {
        foreach ($index as &$value) {
            // Convert ascending
            $value = $value === 'asc' ? 1 : $value;

            // Convert descending
            $value = $value === 'desc' ? -1 : $value;

            // Convert geo to 2d
            $value = $value === 'geo' ? '2d' : $value;
        }

        return $index;
    }