Previous work processes 3D data using either voxel-based or point-based NN models. However, both approaches are computationally inefficient. The computation cost and memory footprints of the voxel-based models grow cubically with the input resolution, making it memory-prohibitive to scale up the resolution. As for point-based networks, up to 80% of the time is wasted on dealing with the sparse data which have rather poor memory locality, not on the actual feature extraction. In this paper, we propose PVCNN that represents the 3D input data in points to reduce the memory consumption, while performing the convolutions in voxels to reduce the irregular, sparse data access and improve the locality. Our PVCNN model is both memory and computation efficient. Evaluated on semantic and part segmentation datasets, it achieves much higher accuracy than the voxel-based baseline with 10 GPU memory reduction; it also outperforms the state-of-the-art point-based models with 7 measured speedup on average. Remarkably, the narrower version of PVCNN achieves 2 speedup over PointNet (an extremely efficient model) on part and scene segmentation benchmarks with much higher accuracy. We validate the general effectiveness of PVCNN on 3D object detection: by replacing the primitives in Frustrum PointNet with PVConv, it outperforms Frustrum PointNet++ by 2.4% mAP on average with 1.5 measured speedup and GPU memory reduction.

Many improvements over previous results are numerically quite small and it is unclear if these improvements are statistically significant. This includes the following points: - No baseline result (e.g. Why not show voxel and point cloud based methods in both graphs? It is hence not clear how much of the improvement is due to the concrete implementation vs. the proposed method. Maybe it would even make sense to combine the proposed method with sparse convolutions?

This work proposes an efficient method for processing 3D data in deep neural networks. The method is evaluated on competitive benchmarks and shows consistent improvements in efficiency while retaining or even improving predictive accuracy. The authors promise to make the code available. Three expert reviewers initially assessed the work as 7/8/6, with minor concerns. The authors provided a detailed rebuttal that was read and discussed by all reviewers.

Previous work processes 3D data using either voxel-based or point-based NN models. However, both approaches are computationally inefficient. The computation cost and memory footprints of the voxel-based models grow cubically with the input resolution, making it memory-prohibitive to scale up the resolution. As for point-based networks, up to 80% of the time is wasted on dealing with the sparse data which have rather poor memory locality, not on the actual feature extraction. In this paper, we propose PVCNN that represents the 3D input data in points to reduce the memory consumption, while performing the convolutions in voxels to reduce the irregular, sparse data access and improve the locality.

Previous work processes 3D data using either voxel-based or point-based NN models. However, both approaches are computationally inefficient. The computation cost and memory footprints of the voxel-based models grow cubically with the input resolution, making it memory-prohibitive to scale up the resolution. As for point-based networks, up to 80% of the time is wasted on dealing with the sparse data which have rather poor memory locality, not on the actual feature extraction. In this paper, we propose PVCNN that represents the 3D input data in points to reduce the memory consumption, while performing the convolutions in voxels to reduce the irregular, sparse data access and improve the locality.