This paper proposes a method for measuring the sag of power transmission lines using unmanned aerial vehicle (UAV) photography data. It combines UAV sampling data with differential positioning for precise target positioning and integrates measured data with catenary theory formulas for accurate sag description. ANSYS finite element simulation software is then used to analyze sag parameters. Experimental results show that this method ensures a measurement error within 4.21%
providing high measurement accuracy and meeting daily detection requirements for transmission line sag.