The thesis titled "Analysis of the Quality of the Geodetic Network for the Construction of the Bakovac - Lika Tunnel Using JAG3D Open-Source Software" focuses on evaluating the quality of portal micro-networks for the construction of the Bakovac - Lika Tunnel using the open-source JAG3D software. The thesis begins with an overview of the history and methodologies of tunnel construction. It discusses the establishment and implementation of geodetic networks for special purposes, highlighting the key steps of planning, execution, and error analysis in geodetic measurements. The practical part includes terrestrial measurements within microtriangulation networks in Bakovac and Lipovo Polje. The collected data were processed and analyzed using JAG3D, ensuring the high precision required for the geodetic foundation of the tunnel. The thesis uses the JAG3D software, developed by Dr. Michael Losler, which is designed for the adjustment and analysis of 1D, 2D, and 3D geodetic networks using the least squares method based on the Gauss-Markov model. The software's capabilities include the adjustment of GNSS baselines, data analysis, and statistical testing using Baarda's global test and data snooping method. The research demonstrates how JAG3D supports network optimization and deformation analysis, which is crucial for identifying shifts or deformations within the network. In conclusion, the thesis confirms that the application of JAG3D software significantly improves the accuracy and reliability of geodetic networks in tunnel construction, providing a robust framework for future geodetic projects