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Recently, a large scale of passenger-dedicated railway construction is blooming in our country. For the sake of high-speed train running and overcoming the difficulty of line maintenance, the ballastless track with better smoothness and little maintenance, is applied widely. What makes the ballastless track significantly different from the ballast one are the higher precision demand of slab and track lying, as well as the smaller adjustment of track slab installation.Therefore, it sets a higher demand for GPS control network of high-speed railway.In common railway surveying and design which is based on state coordinate system, 25mm/km, the distortion error in length, is acceptable, but not in high-speed railway, where, for higher precision, the error is essentially no more than 10mm/km.In some railway construction,narrowing the projection zone could ensure the distortion error below 10mm/km to satisfy the demand, but it comes with a series of problems, such as too many projection zones and coordinates systems in one line, minute and complicated computation of projection zone conversion, relative precision decline between adjacent points after projection zone conversion and so on, bring great inconvenience into the future work as surveying, design, construction, operation and detection.Based on the above issues, firstly the paper discusses the traditional way in data processing of GPS control network, and systematically analyzes the figures and treatment of length distortion in the network.Then, combined with the long control range and small projection distortion in GPS control network of high-speed railway, in this paper a new method named Subsection Orientational Sequential Adjustment, SOSA for abbreviation, is put forward. That is the "subsection" replaces the "projection zone", the direction after the whole network adjustment computation ensure it unique the axes of all coordinate systems in the network, and the adjustment computation goes from one side of the line to the other one by one. In the coordinate system establishment and the network adjustment computation of CP I control network of high-speed railway, the theoretical analysis and the contrast between calculated length and measured length with total stations have proved that, when using SOSA method, the projection distortion error of length is smaller and the projection plane is closer to the groud and so the coordinate system satisfies the demand of building an independent engineering coordinates system. To use SOSA method in GPS zonary engineering control network, it realizes the only one coordinate system in one line without computation of projection zone conversion, which lays the foundation for achieving the goal of small distortion and no conversion in GPS control network of high-speed railway, and creates the conditions to found a high precise GPS plane control network that can serve surveying, design, construction and operation as a tri-network-integrating-one network.At last, according to the principle of SOSA, grounded on the program design platform of Microsoft Visual Studio 2008, General Data Processing Software for GPS Control Network of Precise Engineering, SOSA GPS for short, has been developed with C#. The software supports various baseline formats and ellipsoid parameters, has precision evaluation of apriority and posteriority, and beside all of common data processing methods to GPS control network, SOSA method works well, which can gain the fruit of high precision、little distortion、no conversion in the whole line in a larger scale of CP I GPS control network of high-speed railway.
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