Research And Implementation Of GNSS Real-Time Data Stream Service Software

Data stream, as a data-intensive application with high timeliness, is widely used in various fields such as satellite positioning navigation, video surveillance, the financial industry and so on. In the model of data stream, the data will receive new data ceaselessly in the data receiving end like the flowing water in the water pipe. In terms of the model of data stream,it is the research focus to deal with the data carried in the data stream efficiently and timely.The paper mainly studied how to realize the processing of GNSS real-time data stream in an efficient and timely way. It not only made the processing of data stream come true in an efficient and timely way, but also conducted visual display in terms of the processing results of data stream, so that users would be able to make further analysis and decision making for the data results.First of all, the paper analyzed the functional requirements of the system and proposed an idea for BINEX data stream to transcode to RTCM data stream in accordance with the characteristics of GNSS data stream. Besides, it also envisaged that it might probably be achieved that multiple receivers at the present stage could use the real-time data stream jointly, and all roles contained by NTRIP agreement might be designed, including the transfer,authentication, subscription, and management and resolving and so on in the data stream.Furthermore, the paper conducted in detail the analysis design and implementation of each functional module involved in the GNSS data streaming service software, mainly including BINEX real-time data stream transfer code to RTCM real-time data stream, the management and retransmission of data stream, resolving of data stream, and the visual function module aimed at the results of data resolving. Data stream transfer code module could output the receiver of RTCM data stream to provide RTCM data for other modules, which is the foundation of the whole system. The data stream management and retransmission module, as the core of the system, could provides users with service functions about data stream management, certification and subscription. The consumer of data stream is data stream resolving module, which could provide users with final results of visualization coordinated with data visualization, to help users monitor the real-time data stream, so that the data quality analysis and the relevant decisions could be made.By means of the characteristics of data stream itself, the data resolving module divides the real-time data stream into two stages: data package extracting and data package analysis. Among them, the data package extracting stage is to divide the data steam into individual data package which can be analyzed. The paper respectively achieved corresponding data package extracting algorithms for BINEX and RTCM coded formats. At the data packet analysis stage, the data packet would be classified first according to the message types carried by data package. At last, different analytical work would be carried out for different massage types.The paper defined a unified programmatic interface for analytical operation in order to meet the functional expansion need due to the expansion of message types. Actually, data stream management and retransmission module itself is a background daemon process run in the computer operating system, which listens to the request of Ntrip Server and Ntrip Client and distinguishes them according to the contents of the request message. For the request sent by Ntrip Server, it will receive the data stream transmitted by Ntrip Server after it analyzes it and verifies its identity, while for the request sent by Ntrip Client, after analyzing it, it will transmit the requested data stream if and only if the requested identity is verified and the requested data stream does exist. The management configuration and resolving effect of data stream could both conduct user interaction through a graphical interface.In the end of the paper, respective test cases were designed and testing verification was conducted aimed at data stream transfer code, data stream management and retransmission,data stream resolving and visual functional modules, using the experimental results to verify their validity. The content of the paper is able to achieve the real-time visualization for the processing, retransmission and resolving message of GNSS real-time data stream.