Gps Positioning Technology Used In The Highway Control Survey

Global Positioning System(GPS) is advanced navigating and positioning technology based on modern science. Due to its advantages over traditional surveying GPS surveying is getting more and more important in surveying engineering. Consequently, the related technique and knowledge are well developed. GPS technology together with Remote Sensing(RS) and Geographical Information System(GIS) technology is applied to surveying engineering ,which contributes greatly to the conversion from traditional surveying to digital one.GPS technology has got improved a lot in many fields. For example, the performance of GPS receivers gets higher and some technologies such as DGPS differentiate positioning and RTK differentiate positioning are exerted. In addition, the SA policy was abolished. As a result, GPS positioning can meet the needs of high precision and low consumption of time. Thus GPS surveying is applied to lots of fields such as land navigation, establishment of various levels of controlling nets, precise surveying, layout surveying and so on. Not exceptionally GPS surveying is attractive to highway reconnaisance. Meanwhile, the application of GPS surveying in highway reconnaisance may put forth some questions and problems, to which the solutions are given in the paper. Some significant conclusions are acquired by making experiment and analyzing the data obtained I Distortion of projection length.As for long-distance highway project, the distance from different part of the highway to central meridian varies, because of which the distortion of projection length varies. And positioning precision of different measurement segment is not the same. In principle the projection length distortion should be analyzed and the adjustment should be added. But if the project does not range much in the east-west direction, the above mentioned compensation can be omitted. Nevertheless, GPS surveying of highway reconnaissance often covers long distance amounting to even several hundred kilometers. In such case, the projection length distortion ofdifferent section of the project varies greatly. So the adjustment has to be made.In this paper, the equation of projection length distortion is given. Also some figure isdrawn to illustrate the relationship, When the projection length distortion is out of thelimitation, three set of such coordinate systems are put forward in the paper.II Height measurement Height data obtained by GPS surveying is geodetic height, while the height system adoptedin China is normal-orthometric height system. Thus the GPS geodetic height has to be transferred to normal-orthometric height. In this paper, an approximation model is given. And the least squares approximation is used. Outcome by different methods is analyzed, which leads to significant conclusions.In brief, the above-mentioned problems commonly exist in GPS highway surveying projects. And the solutions given in the paper is valuable for the execution of the surveying engineering. Furthermore, the least squares approximation is introduced as a calculating method, which is theoretically creative.