MightyLittleGeodesy (nuget): You can translate both ways between coordinate systems: RT90, SWEREF99 andWGS84.        The WGS84 object can parse out positions from strings in DMS (degrees, minutes seconds, and DM (degrees, minutes) format.        All in all it’s a pretty easy to use and powerful library.
Keywords: RT90|SWEREF99|WGS84|Geodesy