  This paper proposes RIU-Net (for Range-Image U-Net), the adaptation of a
popular semantic segmentation network for the semantic segmentation of a 3D
LiDAR point cloud. The point cloud is turned into a 2D range-image by
exploiting the topology of the sensor. This image is then used as input to a
U-net. This architecture has already proved its efficiency for the task of
semantic segmentation of medical images. We demonstrate how it can also be used
for the accurate semantic segmentation of a 3D LiDAR point cloud and how it
represents a valid bridge between image processing and 3D point cloud
processing. Our model is trained on range-images built from KITTI 3D object
detection dataset. Experiments show that RIU-Net, despite being very simple,
offers results that are comparable to the state-of-the-art of range-image based
methods. Finally, we demonstrate that this architecture is able to operate at
90fps on a single GPU, which enables deployment for real-time segmentation.
