Using UAVs and robotic total stations in determining height differences when crossing obstacles.

• An unmanned aerial vehicles assisted height transmission method is proposed. • The uncertainty sources of the proposed method are analyzed. • Experiments show it can achieve an accuracy comparable with third-level levelling. • Higher efficiency can be obtained between obstructed benchmarks. When benchmarks are blocked by obstacles such as buildings, woods, hills, etc., it is time- and energy-consuming to acquire the height differences between them through classical geometric levelling because of the detour. Therefore, this paper proposes the combination of unmanned aerial vehicles (UAVs) and robotic total stations in determining height differences across obstacles. Carrying a 360° prism as the target and hovering in the air, the UAV can be sighted by both calibrated and synchronized robotic total stations near two benchmarks to conduct synchronous observations with the help of the automatic target recognition (ATR) and tracking systems. And the height difference between them can be calculated based on the principle of trigonometric levelling. The uncertainty sources that affect the accuracy of the proposed method are analyzed and the main observation procedures for practical use are provided. The results of experiments verify the feasibility, effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]