| With the construction of various Continuously Operating Reference Station (CORS), the network RTK consisting of multi-base stations appears and ravel out the limitations of tranditional RTK technique, which including some shortcomings of error increasing along with distance, dependability and feasibility debasing with baseline increasing, limitation of data transmission methods. Because of the advantages of fargoing overlay, high positioning precision and dependability, VRS technique is becoming one of the most popular network RTK techniques. It is a kind of GPS real-time kinematic positioning technique which makes use of original data observated by multi-base stations to simulate a set of reference station data (including reference station coordinate and GPS carrier phase observation data) near rover station. Consequently, VRS is carrying out the simulation and reconstruction of reference station data and real-timely providing high precision navigation information. Shanghai has already established Virtual Reference Station network system covered with nine GPS base stations. Due to the VRS positioning results belonging to WGS-84 coordinate system and the top-secrecy of local coordinate transform parameters, projection center and other important information, this paper mainly researches the the transform of WGS-84 and local plane coordinate, the realization of serialport communication between GPS and PDA, which based on Windows Mobile 5.0, the sokect network communication based on TCP/IP. On the base of these researches, a set of coordinate transform service system is designed with a purpose of real-timely obtaining local coordinates calculated by server through wireless internet (CDMA/GPRS). Through the continual design and experiment of connection, client validation and data transmission between server and client, this system is successful to achieve data transmission and reception safely and stably. This paper programs all by C# language.
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