GDP: an open-source GNSS data preprocessing toolkit

GNSS Data Preprocessor is a multi-GNSS data preprocessing software designed to process raw GNSS observation data in the Receiver Independent Exchange Format 2.x to 3.x standard. Published under a free and open-source license, LGPL (GNU Lesser General Public License), written in object-oriented programming language C#, it mainly includes multi-GNSS file and IGS product automatic acquisition, format conversion, file selection, data visualization, and analysis of GNSS observation files. It provides both a Windows form interface and a command shell interface for the Windows, Linux, or macOS operating system. Volunteers can also participate in and improve the software through GitHub. This software is continuing to evolve, improving its functionalities according to the updates introduced by the collaborators. We give a brief introduction to the software, including software architecture, functions, and modules. Lastly, we give several common examples, including parallel computing, visual satellite graphical display, and cycle slip detection, to show the working status of the current version of the software.