Cost-Sensitive Hybrid Transformer–Graph Neural Networks for Sparse LiDAR Object Detection in Automated Driving
摘要
Existing LiDAR perception frameworks predominantly assume dense point clouds and balanced class distributions, limiting their practical utility when deployed with cost-effective low-channel sensors operating under severe long-tail object frequencies. Single-paradigm architectures exhibit complementary structural weaknesses: attention-based models capture global context but underspecify local geometric relations, while graph models encode spatial neighbourhoods but may fail to integrate long-range dependencies. Motivated by this gap, this study evaluates object-level 3D detection — the joint prediction of semantic class and oriented bounding box from seven-dimensional geometric descriptors extracted from annotated Velodyne VLP-16 frames — across four architectures: a Transformer FCN, an enhanced spatial GNN FCN, and two hybrid variants that integrate both paradigms through different cross-attention fusion orderings. Experiments are conducted on 2,591 real-world frames annotated for six categories (car, cyclist, human, wall, tree, cart) using file-level disjoint splits with verified zero data leakage. Cost-sensitive learning is embedded within a unified multi-task objective combining classification and 3D bounding-box regression. The best-performing hybrid, Transformer→GNN FCN (Architecture D), reaches mAP (AP@0.5) of 0.881 with mean IoU of 0.829 at ≈ 1,845 FPS (model forward-pass inference), while sustaining strong localization for safety-critical minority classes: IoU 0.919 on cart and 0.895 on human. Pairwise Wilcoxon signed-rank tests with Bonferroni correction confirm statistically significant improvements over all single-paradigm baselines (p < 0.001), supporting hybrid attention–relational architectures as a promising direction for sparse LiDAR perception tasks relevant to ADAS and collision avoidance.