A vision-based pruning algorithm for cherry tree structure elements segmentation and exact pruning points determination

摘要

• A novel vision-based algorithm for pruning dormant cherry trees. • Methodology based on strict pruning rules for the Central Leader Training system. • Easily adaptable methodology to different tree types by adjusting the pruning rules. • Dormant cherry tree pruning can be automated with average accuracy of 93.33 %. The lack of adequately skilled seasonal workforce for agricultural precision tasks such as pruning boosted the development towards automation. Robotic tree pruning, however, requires high precision in determining pruning points and needs to be based on specific pruning practices to be effective. This work presents the first machine vision-based complete algorithm following strict and precise pruning rules for dormant cherry trees of the Central Leader training system, aiming to guide automated cherry pruning. First, multi-class semantic segmentation is performed by testing U-Net with three different feature extraction backbones, to detect the best performing combination. Then, geometrical calculations based on specific pruning strategies are employed to locate the exact cutting point on the detected trunks, branches and shoots. Segmentation results reported an IoU of 98.5 % for three classes (trunk, branches, shoots) by using U-Net with VGG16. We also validated the performance of cutting points determination method, achieving an average accuracy rate of 93.33 %, reporting 88.75 % precision for cutting points on branches, 91.25 % on shoots, and 100 % on trunks, across eight trees. The proposed methodology is the first in the bibliography to propose a vision-based precision pruning algorithm, based on strict pruning rules, that moreover determines the exact pruning points for the Central Leader Training System for dormant cherry trees. Moreover, the adopted pruning strategy can be used for the annual formulation of tree shape, aiming to cover all types of selective pruning tasks, while it can be easily adapted to fit the pruning practices of other tree types by modifying the pruning rules.