FastBEVFusion hit over 50 FPS on nuScenes by fusing LiDAR and camera in semi-aligned BEV spaces, skipping depth estimation entirely
AspireAI community · arXiv
Real-time 3D detection for autonomous driving has a latency budget, and the paper makes the arithmetic explicit: at 120 km/h a vehicle needs 72 meters to stop, so a 333 millisecond recognition system adds 10 meters of braking distance while 20 milliseconds, which is 50 FPS, adds only 66 centimeters. FastBEVFusion takes a simple route to that budget. It projects modality-specific features into semi-aligned modality-specific bird's-eye-view spaces instead of relying on computationally intensive and error-prone depth estimation, then fuses them with a lightweight soft dynamic module built on cross-attention that adapts to scene context and fuses across the whole BEV space. On nuScenes it outperforms state-of-the-art real-time systems and runs at over 50 FPS without deployment libraries, while staying robust to calibration errors. The limitation is that all results come from the nuScenes benchmark rather than a deployed vehicle.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.