I. Introduction
In recent years, power demand is rapidly increasing with the continuous development of economy, and the scale of power grid is also continuously expanded in various countries. Thus the problem of grid security has attracted more attention, for what a key issue is to ensure the safety and reliability of power grid by transmission line inspection. Traditional manual inspection is time-consuming, ineffective and high-risk, which is unable to meet the needs of ‘Smart Grid’. With the rapid development of UAV (Unmanned Air Vehicles), UAV-based inspection has become the new trend for transmission line inspection, considering the agility, high efficiency and speed, etc.