GKit-SSRDecoder: An Open-Source C/C++-Based PPP-B2b and HAS Decoding and Formatted Product Generation Software

With the rapid development of Real-Time Precise Point Positioning (RT-PPP), the BeiDou-3 PPP-B2b and Galileo High Accuracy Service (HAS) have become pivotal for providing free, global, satellite-based precise correction services. However, most existing open-source decoding tools are developed based on the Python language, which limits their integration into embedded systems and real-time C/C++ positioning frameworks. In addition, these raw data streams lack standardized input formats and product generation, and do not take into account user-side satellite antenna calibration, which hinders offline analysis and cross-platform verification. To bridge these gaps, this study develops and presents the GKit-SSRDecoder, an open-source, high-performance C/C++-based software designed for the end-to-end processing of PPP-B2b and HAS messages. The software features a modular architecture that supports multi-receiver raw data stream parsing, State Space Representation (SSR) message decoding, and the automated generation of RINEX-compliant precise orbit, clock, and code bias products. Comprehensive evaluations were conducted using data from diverse GNSS receivers and compared against post-processed products. The results demonstrated that the Signal-In-Space Range Errors (SISRE) for the PPP-B2b service is 0.093 m and 0.086 m for GPS and BDS-3, respectively, while the HAS service achieves 0.057 m for GPS and 0.048 m for Galileo. Positioning tests showed that the generated products enable RT-PPP to reach centimeter-to-decimeter-level accuracy in static and kinematic modes. Specifically, in real-time kinematic scenarios, the positioning performance of the PPP-B2b and HAS services achieves RMS values of 0.13/0.11/0.12 m and 0.18/0.12/0.23 m in the East/North/Up directions, respectively. This software serves as a useful and portable tool for the GNSS community, facilitating the industrial application and scientific research of satellite-based augmentation services.