This lecture covers the fundamentals of geodesy, focusing on coordinate systems and their applications in GPS technology. It begins with an introduction to geodesy, defining it as the science that studies the geometric shape of the Earth and its gravitational field. The instructor discusses various coordinate systems, including local Swiss systems and global systems like WGS84, emphasizing the importance of accurate geodetic references in a dynamic environment. The lecture also addresses the principles of GPS technology, explaining how GPS receivers measure distances and the concept of pseudo-distance. The instructor highlights the main sources of error in GPS measurements and the necessary conditions for accurate positioning. Additionally, the lecture includes practical examples of data collection and analysis, demonstrating how geodesy is applied in real-world scenarios. The session concludes with a discussion on the tectonic movements of the Earth's plates and their implications for geodesy, reinforcing the interconnectedness of these concepts in understanding Earth's dynamics.