Fig. 4

The Stem detection results in relation with the trajectory of data collection. a The trajectory and the inside-canopy-ULS point cloud. The green square marks the effective area of data collection, which was defined according to distribution of the under-canopy trajectory and the locations of the hover-rotation model of the UAV; b Results of manual stem detection with the spatial distribution of inside-canopy-ULS data at the background. Purple dots represent the reference trees whose stems were manually detected, green dots represent the reference trees that were manually undetected; c Results of the automated stem detection. A reference tree is marked with a blue ‘+’ when outside the effective area, and with a red ‘x’ when inside the effective area. A detected tree is marked with an orange circle and a yellow square when inside and outside the effective area, respectively