This lecture covers the fundamentals of geodesy, focusing on the Earth's reference systems and coordinate transformations. It begins with a review of satellite localization and the introduction of geodesy concepts, including units and coordinate systems. The instructor discusses GPS technology, addressing questions about GPS measurements, pseudo-distances, and sources of error. Key topics include geodetic references such as the geoid and ellipsoid, and the Swiss local system CH1903 compared to the global WGS84 system. The lecture emphasizes the importance of understanding the Earth's shape and gravitational field in defining altitudes and coordinates. The instructor explains the challenges of creating a stable coordinate system for the dynamic Earth and the significance of physical models in geodesy. The session concludes with a discussion on coordinate transformations and the implications for practical applications in construction and land management, highlighting the necessity of accurate geodetic data for effective project planning.