【正文】 hnology , bining with modern muni cation technology， to a revolutionary change. The method for simultaneously determ ineing three dimensional coordinates by GPS has changed the traditional positioning technology from land with inshore to entire ocean and outer space, from statics to kinematics, from point positioning to work difference, from afterwards processing to realtime positioning and navigation, and absolute and relative positioning pr233。 GPS observation data by means of diferential processing of carrier phases, consequently calculate the spatial location information of the mobile stations, whose positioning precision can increase. T he method above is named DGPS technology. In general, GPS reference station should be set up in the supervisory center for the sake of convenient supporting pow er, management and maintenance. To ensure the supervisory precision, it is stressed that the distance between the GPS reference station and the construction area must be less than 56 km, and the distance controlling requirement can be satisfied in practice. 1. 1. 4 Mobile terminal Mobile terminal includes systemrequiring equipments installed in the project supervisory car and roller paction machines. 1) Mobile terminal installed in the roller paction machine A mobile terminal installed in a roller paction machine is mainly posed of an integrated system unit, a GPS receiver antenna and a wireless munication antenna. The system unit integrates main equipments of industrial platform puter, GPS receiver, wireless munication and so on. Mobile terminal is mobile super visory equipment like GPS moving station, and carries out GPS mobile observation. Its control items mainly include the rolled track, rolled speed, and rolled times of the roller paction machines. Mobile terminals feed back the effective observation result to the supervisory center continuously and realtimely. Meanwhile, the platform puter reflects the work status of the roller paction machine realtimely, by means of figures and tables in the system unit of driver＇ s cab of the roller paction machine. The operator of the roller paction machine can check out whether his or her work meets the quality requirement on the display screen. 2) Mobile terminal installed in the project supervisory car Project supervisory car is the working vehicle for construction quality super vising that is equipped exclusively for the project main tasks are carr ying out GPS mobile observation and supervising locale quality . Its main items of observation are the thickness variations of paving layer before and after the pact ion, supporting data for controlling the paving thickness and roughness of filling layer and calculating the pacted rate. T he supervisory car also feeds the observation results back to supervisory center. Besides, according to the system supervisory data, it conducts the locale construction from the point of riew of quality management .Mobile terminal installed in the project supervisory car and mobile terminal installed in the roller paction machine resemble each other. 1. 2 Main characteristics of the system Main characteristics of GPS realtime supervisory system are as follows. 1 ) Continuous realtime supervision. Data munication achieves bidirect ional transmission in a real sense. The movement tracks and velocities of the roller paction machines can be displayed realtimely , and three dimensional location information at the sampling rate of one second can be displayed realtimely on the display screen, no matter whether it is in the supervisory center, on locale subsuper visory station or in mobile terminals. The observation data of the system are cont inuous, and the processed results at interval of one second meet enough the need of continuity of supervisory data from the system. 2) High degree of automation. In the whole system, it is fully automatic that emitting the differential data of reference station to mobile terminals, feeding back the position information of terminals to supervisory center, displaying the movement track and velocities of all roller paction machines both in the supervisory center and in the mobile terminals, storing and proceeding data and feedback analyzing , etc. 3) Easy and convenient operation. The supervisory center and work relay station of the system are designed fully according to the need of full automation, and the parts operated manually mainly concentrate on mobile terminals. T he operation of the mobile terminals is very easy and convenient, which contains only several simple necessary steps such as turning on and off the unit , the equipment s of mobile terminal are pact , of small weight and size and its loading and unloading is also very easy. 4) High precision. Thank to GPS RTK technology adopted for data processing of the system and the distance between the mobile terminals of Shuibuy a project and GPS reference station does not exceed 3 km, it s horizontal precision achieves 177。t make destruction to the system equipment , in this way,exclusive power ponent and relevant cable conductor and adapter connector are designed and produced. 3 Elevation accuracy analysis of the system In order to evaluate the elevation accuracy of the system, on a filling surface of the experimental field, using a light car and taking the movement track covering the whole surface almost even, three groups of data of the same elevation surface are obtained. One group of movement track is illustrated as Fig . 2 ( the unit is meter) . As far as three groups of data collected in the experiment are concerned, because the velocity of the car are different and interval distance of two neighbored track line are unequal, the amounts of dots of the groups are different , they are 906, 922 and 639 respectively. It is necessary to