Automatic extraction of individual tree branch structure parameters from terrestrial laser scanning data

Objective: Using terrestrial laser scanning (TLS) data to extract skeleton of individual tree and developing an automatic measurement algorithm of branch structure based on skeleton model for parameterized modeling and visualization simulation of forest. Method: We applied FARO terrestrial laser scanner, with a quarter of the resolution, speed 244000 s-1 to obtain three trees' TLS data. Firstly, skeleton model was generated by SkelTre algorithm using TLS data with noise. Then, we developed a new method to extract branch structure with depth first search algorithm. According to the skeleton model, we searched the branch nodes connecting parent branch with child branch. Each node contained some information about this dominated direction, number of different branches and those coordinates. Due to the position error caused by skeletonization, we adopted the cylinder fitting to correct the extension direction of the branches and reduce the error of the branches' angle estimated by the skeleton model. Finally, we extracted the morphological structure based on the revised branches' angle through verification of total length of the estimated and measured branches. Result: The experimental trees' branch structure was clear. Branch length and angle were all automatically determinated. Primary branches extracted were totally 22 and the secondary branches were 43.Regression equation of the estimated and measured length was Y=1.003X+0.03 which performed with R-squared of 0.998. The root mean square error (RMSE) between estimated length and measured length was 0.029 m. Moreover, regression equation of the branch angle estimated and measured by skeleton model was Y=0.672X+16.779, which performed with R-squared of 0.356 and RMSE of 20.45°. Nevertheless, regression equation of the branch angle estimated and measured by cylinder fitting was Y=1.008X+0.18, it performed with R-squared of 0.975 and RMSE of 3.44°. Conclusion: The algorithm of estimation and extraction based on cylinder fitting could accurately determine branch structure on individual tree. Furtherly, the extracted branches' length performed high precision and cylinder fitting method could effectively improve accuracy of the branch angles estimated by skeleton model. © 2016, Editorial Department of Scientia Silvae Sinicae. All right reserved.