In a UAV system. physical sensor offsets occur between an observation sensor and a GPS/IMU sensor which represents the position of UAV. The difference of angle between the GPS/IMU sensor’s axis and the observation sensor’s axis is referred to as boresight angle. The difference in physical position between the two is referred to as lever-arm. https://www.bekindtopets.com/great-pick-Obsidian-ULU-w-Eagle-clearance/