Dan-Conv: Depth Aware Non-Local Convolution For Lidar Depth Completion

Sparse LiDAR depth completion is a beneficial task for many robotic applications. It commonly generates a dense depth prediction from a sparse depth map and its corresponding aligned RGB image. This image-guided depth completion task mainly has two challenges: sparse data processing and multi-modality data fusion. In this letter, they are dealt with by two novel solutions: (1) To efficiently process sparse depth input, a Depth Aware Non-local Convolution (DAN-Conv) is proposed. It augments the spatial sampling locations of a convolution operation. Specifically, DAN-Conv constructs a non-local neighbourhood relationship by exploiting the intrinsic correlation among observable depth pixels. In particular, it can readily replace standard convolution without introducing additional network parameters. (2) A Symmetric Co-attention Module (SCM) is proposed to fuse and enhance features from depth and image domain. It estimates the importance of complementary features by the co-attention mechanism. Finally, a neural network built on DAN-Conv and SCM is proposed. It achieves competitive performance on the challenging KITTI depth completion benchmark. Comparing to approaches with approximate accuracy, this lightweight network requires significantly fewer learnable parameters.