  LiDAR and camera are two critical sensors for multi-modal 3D semantic
segmentation and are supposed to be fused efficiently and robustly to promise
safety in various real-world scenarios. However, existing multi-modal methods
face two key challenges: 1) difficulty with efficient deployment and real-time
execution; and 2) drastic performance degradation under weak calibration
between LiDAR and cameras. To address these challenges, we propose CPGNet-LCF,
a new multi-modal fusion framework extending the LiDAR-only CPGNet. CPGNet-LCF
solves the first challenge by inheriting the easy deployment and real-time
capabilities of CPGNet. For the second challenge, we introduce a novel weak
calibration knowledge distillation strategy during training to improve the
robustness against the weak calibration. CPGNet-LCF achieves state-of-the-art
performance on the nuScenes and SemanticKITTI benchmarks. Remarkably, it can be
easily deployed to run in 20ms per frame on a single Tesla V100 GPU using
TensorRT TF16 mode. Furthermore, we benchmark performance over four weak
calibration levels, demonstrating the robustness of our proposed approach.
