Post-Processing Geometry Enhancement for G-PCC Compressed LiDAR via Cylindrical Densification

The geometry-based point cloud compression algorithm achieves efficient compression and transmission for LiDAR point clouds with high sparsity. However, the low-bitrate mode results in severe geometry compression artifacts, which involve both point reduction and coordinate offset. To the best of our knowledge, this is the first attempt to directly enhance the geometry quality for compressed LiDAR point cloud (CLGE) in a post-processing manner. Our proposed method consists of two branches: cylindrical densification and adaptive refinement. The former adopts a multi-scale sparse convolution framework to effectively extract spatial features in the cylindrical coordinate system and generate dense candidate points quickly. Large asymmetric sparse convolution kernels are also designed to capture the shapes of different regions and objects. The latter branch refines the candidate points through several MLP layers, which takes the neighborhood features between the candidate points and the input points into account. Finally, the designed ring-based farthest point resampling serves as an effective alternative for achieving the target number while maintaining the geometry distribution. Extensive experiments conducted on several datasets verify the effectiveness of our approach under different compression artifact levels. Furthermore, our method is easily extended to upsampling and is robust to noise. In addition to the geometry signal quality improvement, the point cloud enhanced by our proposed method alleviates the performance degradation in object detection task due to compression distortion.