Abstract: The morphology and structure of plants were complex. It is of great significance to investigate the inherent motion law of plants under the action of external force, such as realistic animation formation, plant pruning, vibration picking and forest protection. A low cost outdoor tree complex motion capture method was explored, and the relationship between the stem motion and the external force was analyzed. The Kinect was used to capture the branches motion; MeanShift algorithm was used for tracking branches markers and the three-dimensional trajectory of the trunk was extracted according to the principle of Kinect coordinate transformation. A method of measuring the motion of a branch with relative deflection angle was proposed, and the frequency domain signal was obtained by the FFT transform of the deflection angle signal in time domain. Experimental results show that the trajectory of the tree trunk and branches under the action of external force is periodic motion of approximate circular; the sway frequencies of the trees under various external forces are almost same. Extra experiments indicate that there are differences in the sway frequency of the same tree with different tree structure.

Key words: tree branch motion, motion capture, trajectory, sway frequency, Kinect