Rapeseed population point cloud completion network (RP-PCN) with dynamic graph convolution for 3D reconstruction of crop canopy occlusion architecture

Abstract: Quantitative descriptions of complete canopy architecture are crucial for evaluating crop photosynthesis and yield to guide ideotype design. Although three-dimensional (3D) sensing technologies have been developed for plant and canopy reconstruction, severe occlusion and complex architectures hinder accurate canopy descriptions. In this study, we propose a point cloud completion model for 3D reconstruction of rapeseed populations from seeding to silique stages using multi-view imaging. A complete point cloud generation framework was developed with the virtual-real integration (VRI) simulation method and occlusion point detection algorithm to annotate the training dataset by distinguishing surface from occluded points. The rapeseed population point cloud completion network (RP-PCN) was designed with a multi-resolution dynamic graph convolutional encoder (MRDG) and point pyramid decoder (PPD) to predict occluded points based on input surface point clouds. A dynamic graph convolutional feature extractor (DGCFE) was introduced to capture structural variations across the growth period. The effectiveness of point cloud completion was validated by predicting yield using architectural indicators from complete point clouds of rapeseed population. The results demonstrated that RP-PCN achieved chamfer distance (CD) values of 3.35 cm, 3.46 cm, 4.32 cm, and 4.51 cm at the seedling, bolting, flowering, and silique stages, respectively. Ablation studies showed the effectiveness of the MRDG and DGCFE modules, reducing CD values by 10% and 23%, respectively. The silique efficiency index (SEI) from RP-PCN improved yield prediction accuracy by 11.2% compared to incomplete point clouds. The RP-PCN pipeline proposed in this study has the potential to be extended to other crops, significantly enhancing the analysis of population canopy architectures in field environments.