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SDGOCC: Semantic and Depth-Guided Bird's-Eye View Transformation for 3D Multimodal Occupancy Prediction
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Proposes SDG-OCC, a LiDAR-camera 3D occupancy prediction network with a semantic- and depth-guided BEV view transformation and fusion-to-occupancy-driven active distillation, achieving SOTA mIoU on Occ3D-nuScenes at real-time speed.
Problem
Camera-only occupancy methods lack accurate depth, LiDAR-only methods suffer from occlusion, and LSS-based lightweight pipelines produce sparse, inaccurately estimated BEV features while underusing LiDAR geometry and semantics.
Approach
Refine LSS depth distributions using LiDAR co-point depth diffused within same-semantic regions (from a segmentation head) followed by bilinear discretization, and fuse LiDAR and camera BEV features with neighborhood gated attention, then selectively distill fused knowledge into the camera branch only in LiDAR-occupied regions.
Key results
- SDG-Fusion reaches 51.66 mIoU on Occ3D-nuScenes validation (133 ms), above RadOcc-LC's 49.38 and the camera-only COTR's 46.2.
- SDG-KL reaches 50.16 mIoU on Occ3D-nuScenes at 83 ms, trading a small accuracy drop for real-time speed.
- On SurroundOcc-nuScenes validation, SDG-Fusion reaches 31.7 mIoU, above DAOcc's 30.5 under the standard protocol; visible-mask variants reach 52.2 mIoU.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| add semantic and depth-guided view transformation (ablation) | Baseline occupancy model · Occ3D-nuScenes | mIoU: 37.84 -> 48.51 | Helped |
| add fusion-to-occupancy-driven active distillation (ablation) | Baseline occupancy model · Occ3D-nuScenes | mIoU: 37.84 -> 44.92 | Helped |
| add SDG and FOAD together (ablation) | Baseline occupancy model · Occ3D-nuScenes | mIoU: 37.84 -> 51.66 | Helped |
| use SDG-Fusion instead of RadOcc-LC | Occ3D-nuScenes validation · Occ3D-nuScenes validation | mIoU: 49.38 -> 51.66 | Helped |
| use SDG-KL instead of SDG-Fusion | SDG-OCC · Occ3D-nuScenes validation | mIoU: 51.66 -> 50.16 | Hurt |
| set SDG discretization range r=1 and diffusion layers l=4 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 51.15 | Hurt |
| increase diffusion layers from l=8 to l=12 at r=1 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 51.28 | Hurt |
| set SDG discretization range r=2 and diffusion layers l=4 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 50.4 | Hurt |
| set SDG discretization range r=2 and diffusion layers l=8 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 51.03 | Hurt |
| set SDG discretization range r=2 and diffusion layers l=12 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 51.12 | Hurt |
| set FOAD neighborhood size k=3 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 51.22 | Hurt |
| set FOAD neighborhood size k=5 (ablation) | SDG-Fusion · Occ3D-nuScenes | mIoU: 51.66 -> 51.40 | Hurt |
Limitations
- Performance on SurroundOcc-nuScenes is only comparable, not clearly superior, to the best prior methods under the standard protocol.
- Best SurroundOcc numbers rely on visible masks generated from a prior method, which is a different protocol.
- Hyperparameters (radius, number of diffusion layers, K, alpha/beta) were tuned on the validation set.
Experimental setup
Datasets: Occ3D-nuScenes SurroundOcc-nuScenes
Benchmarks: Occ3D-nuScenes SurroundOcc-nuScenes
Metrics: mIoU IoU per-class IoU FPS inference time (ms)
Baselines: TPVFormer SurroundOcc OccFormer FBOcc PanoOcc FastOcc BEVDet4D FlashOcc COTR HyDRa OCCFusion RadOcc-LC
Builds on: Lift-Splat-Shoot FlashOcc BEVFusion SPVCNN FOAD active distillation idea from prior work
Closest papers by meaning
- Achieving Speed-Accuracy Balance in Vision-based 3D Occupancy Prediction via Geometric-Semantic Disentanglement (AAAI 2025 · similarity 0.90)
- CSV-Occ: Fusing Multi-frame Alignment for Occupancy Prediction with Temporal Cross State Space Model and Central Voting Mechanism (ICML 2025 · similarity 0.90)
- Spatiotemporal Decoupling for Efficient Vision-Based Occupancy Forecasting (CVPR 2025 · similarity 0.89)
- UnO: Unsupervised Occupancy Fields for Perception and Forecasting (CVPR 2024 · similarity 0.89)
- SelfOcc: Self-Supervised Vision-Based 3D Occupancy Prediction (CVPR 2024 · similarity 0.89)
- OctOcc: High-Resolution 3D Occupancy Prediction with Octree (AAAI 2024 · similarity 0.89)
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