Skeleton extraction and pruning point identification of jujube tree for dormant pruning using space colonization algorithm

Front Plant Sci. 2023 Jan 19:13:1103794. doi: 10.3389/fpls.2022.1103794. eCollection 2022.

Abstract

The dormant pruning of jujube is a labor-intensive and time-consuming activity in the production and management of jujube orchards, which mainly depends on manual operation. Automatic pruning using robots could be a better way to solve the shortage of skilled labor and improve efficiency. In order to realize automatic pruning of jujube trees, a method of pruning point identification based on skeleton information is presented. This study used an RGB-D camera to collect multi-view information on jujube trees and built a complete point cloud information model of jujube trees. The space colonization algorithm acts on the global point cloud to generate the skeleton of jujube trees. The iterative relationship between skeleton points was represented by constructing a directed graph. The proposed skeleton analysis algorithm marked the skeleton as the trunk, the primary branches, and the lateral branches and identified the pruning points under the guidance of pruning rules. Finally, the visual model of the pruned jujube tree was established through the skeleton information. The results showed that the registration errors of individual jujube trees were less than 0.91 cm, and the average registration error was 0.66 cm, which provided a favorable database for skeleton extraction. The skeleton structure extracted by the space colonization algorithm had a high degree of coincidence with jujube trees, and the identified pruning points were all located on the primary branches of jujube trees. The study provides a method to identify the pruning points of jujube trees and successfully verifies the validity of the pruning points, which can provide a reference for the location of the pruning points and visual research basis for automatic pruning.

Keywords: dormant pruning; jujube tree; pruning point identification; skeleton; space colonization algorithm.

Grants and funding

This work was supported by the Key R&D Projects in Hainan Province (Grant No. ZDYF2022XDNY231), the National Natural Science Foundation of China (Grant No. 52265040), and the National Natural Science Foundation of China (Grant No. 51765058).