Regional Three-Dimensional Real-Time Positioning Theory And Applications Based On Network GPS And Geoid Determination

In recent years, with the rapid development of GPS technology and (quasi-) geoid technology, GPS positioning accuracy has been improved from the meter-scale to the centimeter level or even higher, while the accuracy of refined (quasi-) geoid has been improved to millimeter level and will become an important alternative to the traditional means of survey. However, with the innovation of GPS technology, people put forward higher requirements for the accuracy, reliability, real-time-ness and validity of the technology. Meanwhile, the continuously operating GPS reference station (CORS or network GPS) and high precision (quasi-) geoid will be or have been gradually established and finished, making the regional surveying and mapping datum real-time and dynamic, and the positioning services based on the two technologies are of great potential for applications and services. Therefore, the study of regional three-dimensional real-time positioning theory based on GPS network and geoid has high theoretical value and practical significance.This thesis, based on an in-depth analysis of continuously operating GPS reference stations network and geoid determination, is focused on the theory and method of regional network GPS system and the establishment of geoid model of precision as high as centimeter level. We have established the Chengdu integrated GPS service network (CDIGN) and high precision (quasi-) geoid model of Chengdu region. Meanwhile, we carried out extensive research on the integrated application of the geoid model and network GPS, including the rapid recovery of regional surveying and mapping datum, geoid model and the CORS system integration methods, the geoid querying system and the traditional height control network system and so on.The main content of this thesis includes the following three parts:1. A comprehensive introduction to the key technologies of establishing GPS network and the basic method of establishing regional geocentric surveying and mapping datum is given, including the GPS carrier phase and code pseudo-range observation equations, the GPS observation error, the method of estimating network ambiguity and the network parameters, the computational model of network RTK and the communication protocol of CORS system, the coordinate conversion and so on. The Chengdu Integrated GPS Network (CDIGN) service system is established, in which the network ambiguities are solved via Kalman filtering and LAMBDA method and the real-time troposphere delay is estimated via the ARSNet/VENUS Venus software. Detailed analysis proved the method is effective and stable.2. The performance test of the network RTK positioning system based on ARSNet/VENUS software shows:Inside the CORS network, the initialization time obeys a uniform distribution with the minimum value of 2 seconds, the maximum value of 103 seconds, and the average value of 9.2 seconds. The initialized time is almost independent to DOP value (when DOP<3). Outside the network, the time is under 6 seconds when the distance is shorter than 30km. With the increase of distance, the time is increased from several seconds to 480 seconds. When the distance is longer than 60km, the initialization process couldn't be finished.The internal coincidence accuracy of single epoch positioning is the same along the north and the east directions, in which the mean square error is±1.0cm, the maximum error is 5cm, and the elevation mean square error is±1.4cm. The difference between the coordinates obtained from two initializations is very small. The absolute positioning accuracy of inside and outside network is uniform. The horizontal accuracy is smaller than 3cm. The geodetic elevation accuracy is smaller than 5cm.In short distance GPS survey, the relative error of distance measurements can be decreased by using synchronized RTK survey. The mean square error of distance decreased to 1/3 of that of the asynchronous measurement, thus fulfill the accuracy requirement of the CJJ73-97 standard.The kinematic positioning accuracy is dependent on the communication condition, the satellites geometric distribution and the observation condition. Under good conditions, the kinematic horizontal accuracy is smaller than±4cm.3. A comprehensive study on the theories and methods of determining geoid has been carried out, including the Stokes theory and Molodensky theory, the geometry, gravity, and combined method, as well as the computation method of quasi-geoid, i.e. the removing-restoring method. The 1'xl'(about 2km) and 2'30"x2'30" (about 5km) grid gravity quasi-geoid models are calculated, using EGM96 and WDM94 as reference gravity field models, for a certain region in the Southwest, China. Field check has been performed to verify the built gird quasi-geoid models that use the WDM94 as the reference gravity field model. The result shows that the external check accuracy of the height anomaly of the 1'and 2'30 "grid quasi-geoid models are±0.009m and±0.017m respectively in this region. The interpolation accuracy of 1 x 1 geometric quasi-geoid model is 2-3 times of that of the gravity grid model of the same grid size. That indicates gravity data is important.On the basis of the above work, a detailed analysis of fitting accuracy of several common interpolation models (weighted average, Shepard surface fitting, Polynomial fitting and mobile surface-fitting) is given. The result shows that the interpolation accuracies are basically the same. It is also shown that in small range and relatively flat areas, the geometric interpolation method can be used directly to achieve high accuracy (cm order of magnitude) of the GPS height transformation.4. With the CDIGN and the 1'and 2'30" grid quasi-geoid models, we have developed the quasi-geoid query system and detected the system error in traditional elevation control network in this area. Rapid recovery of the datum in the region after the 5.12 Wenchuan earthquake has also be done. An integration approach of the determined geoid model based on NMEA0183 protocol or RTCM protocol is proposed, with which the user can immediately get normal height of a point. The first one is a real-time system that defines the communication protocol between the data center and the user. The latter uses the correction of GPS observed distance to achieve real-time conversion from GPS-geodetic height to the normal height.Based on the GPS system and the Galileo system, a preliminary analysis of the GNSS constellation positioning accuracy is provided. The result shows that in terms of the number of observed satellites and DOP values, GNSS system is obviously better than the GPS system alone. When combining the two systems for navigating and positioning, the number of satellite visible usually increases, and the DOP value is normally smaller than the single-system approach. They help overcome the constraints of altitude angle of satellite positioning, and expands the scope of satellite positioning, particularly for built-up urban and mountain environment.