Study On Key Technologies Of GNSS Visual Simulation

Global Navigation Satellite System(GNSS)visual simulation is able to analyze the function and performance of multi-constellation GNSS,and more comprehensively,intuitively and graphically express the space logic relationship among satellites,space environments and users.It is also very useful to the design and analysis of satellite navigation system.In order to solve the problems in GNSS visual simulation,such as the visualization of large scale differences between satellites and earth,GNSS user complicated movement scenario design,GNSS urban canyons visual simulation and analysis,key technologies of GNSS visual simulation are studied.The researches are shown bellow.1.In order to solve the visualization problem of large scale difference between satellites and earth,three methods were proposed.Firstly,in order to improve the visualization efficiency of multi-GNSS satellite orbit model,a new simplified method was demonstrated.This method included the following aspects.The orbit shape of satellites was altered approximately from ellipse to circle.In a same constellation,different values of orbit semi-major axes were unified into one mean value.The values of right ascension of ascending node were clustered and renewed based on K-means algorithm.Secondly,based on level of detail(LOD)technology,multi-scale satellite models were built to improve the visualization efficiency.Thirdly,an algorithm of satellite models feature length based on the location of view point was proposed to finding the proper ratio between satellite and earth.The simulation results manifested that due to these three methods,the render time of the model was reduced while the frames per second were increased.The visualization efficiency of multi-constellation GNSS and earth models were significantly improved.2.According to the different motion characteristics by different users,the GNSS user movement scenario and its contents were defined.GNSS user movement scenario was divided into several parts such as simple movement scenario,car movement scenario,ship movement scenario,aircraft movement scenario and missile movement scenario.Mathematical models of these whole movement scenarios were built.According to different scenarios,modular design methods were proposed.These methods split complex scenarios into simple and independent movement modules such as linear motion module,turning motion module,climbing motion module,holding motion module and along the path point motion module.All the input and output of the basic motion modules were given.The complexities of scenario were decreased and the design and maintenance of scenario were much more simple and convenient by these modular design methods.At last,visual simulations were conducted for car movement scenario and aircraft movement scenario.3.The GNSS urban canyons visual simulation and analysis were studied.A three dimensional LOD urban canyons model was built based on octree structure first.Then on this basis,a comparable fast prediction method was proposed for GNSS satellite visibility determination in urban canyons.In order to reduce the burden of calculation,this method analyses the direction of triangular patches normal vector,the relative position between triangular patches and user,and the occlusion relation between two adjacent moments.Next,a multi-constellation GNSS shadow matching method was put forward to improve the positioning precision in urban canyons.At last,based on fuzzy comprehensive evaluation(FCE)theory,a method to quantitatively evaluate the performance of GNSS,and systematically quantitatively analyze precision,availability,continuity and integrity was proposed.A simulation was conducted to emulate the real environment of urban canyons.Results showed that those methods described above could improve the rendering speed of urban canyons three dimensional models,and predict the performance of GNSS in a specific location and specific time in urban canyons accurately and quickly,so that GNSS users could find a proper time and motion trail to perform a task.4.Based on the methods and algorithms above,a GNSS visual simulation software system was designed and implemented.From the view of software development,the requirements analysis,general design,detailed design and codes implementation were carried out one after another.Function and the relationship between each main part of GNSS visual simulation system such as scenario design module,data processing module,data management module and scenario visualization module were descried in detail.At last,the GNSS visual simulation was implemented by this software system.The function and performance of the simulation system appeased the design requirements.