Modeling And Visualizing The Orbits Of GNSS Satellites On Cesium Platform

With the development of computer and Internet technology,the popularization and sharing of knowledge and information has gradually become the theme of this era.Network has greatly reduced the information inequality of human society:highly academic data is now available for ordinary people to use,and the emergence of many"open source" tools also reduce the cost of application,which finally promotes the prosperity of network products,including Research on GNSS Visualization.Internet provides a wealth of data,information,methods and tools for satellite navigation visulazing research,and people can easily access them.However,the current research on GNSS orbit simulation and visualization is often accomplished by secondary development.This approach not only requires a payment of component purchase fees,also requires researcheres certain navigation and communication expertise,and multiple computer programming capabilities.And the finished products have to be downloaded and installed,whose network communication efficiency is not good enough.Therefore,in consideration of the development costs,communication costs and communication efficiency,this approach does not adapt to web ecosystem well.While,Cesium,the digital earth product running on browsers,can be used as a satellite orbit visualization platform for the high-level programmers or the programming beginners to create GNSS visualization applications,and make up for the deficiencies of the above-mentioned development practice.In this paper,a method based on the Cesium globe for GNSS orbital simulation and visualization is proposed.In this study,the navigation satellite trajectory parameter data published by the authoritative websites are collected.CZML(Cesium Markup Language)is used to record the satellite track data.At the same time,the data-streaming capability of the CZML format and the SSE technology(Server-Sent Event)are combined to transmit the visualization data,thus improving the visualization efficiency and interactive experience greatly.Firstly,the orbital material data,TLE(two rows of root parameters),of the four GNSS system satellites and the space debris,were collected and sorted.Then the astronomical script library(SGP4)tool for Python was used to caculate the trajectory data of each space object,which then are stored with CZML files.And then,the SSE technology is taken to combine with the streaming mechanism supported by CZML format to realize the streaming of the satellite track data on web.Finally,the Cesium platform,as well as its API(application program interface)is used to build an application running on web browsers to visualize the objects' orbits.In addition to showing the trajectory scene,this application also uses Python's PyEphem library to calculate the navigation satellites' other astronomical information,such as the sub-satellite location and the over-forecasting information.This application provides end-users with a good approach to get more comprehensive understanding to the navigation satellites overhead.The method in this paper is based on Cesium digital earth platform.It is low in practice threshold,rich in visual information,highly interactive and flexible in data transmission,and it is also a new data visualization processing workflow in the web enviroment.It will help practitioners and even just enthusiasts to display and exchange the learnings about the motion of earth satellites and space junk,to the general public or the personnel in other research areas,in a more vivid,interesting and yet scientific expression way.And it would in turn help people to leran more about the navigation satellites and get an improved sense of the aerospace.