The coding style and the design of the class is below mediocre. It's downright bad.
The classes provide a NMEA parser that at the same time mixes into its functionality Windows port connection and MySQL database stuff.
It's reusability, code-wise, is converging to 0 fast. The coding style and comments are also very poor and not in English, respectively.
I would recommend a full re-write, preceded by a period of at least 5 minutes of thinking about reusability of the components and their relationships (i.e. port connection versus database storage versus NMEA input parsing etc.)