RI-Fusion: 3D Object Detection Using Enhanced Point Features With Range-Image Fusion for Autonomous Driving

The 3D object detection is becoming indispensable for environmental perception in autonomous driving. Light detection and ranging (LiDAR) point clouds often fail to distinguish objects with similar structures and are quite sparse for distant or small objects, thereby introducing false and missed detections. To address these issues, LiDAR is often fused with cameras due to the rich textural information provided by images. However, current fusion methods suffer the inefficient data representation and inaccurate alignment of heterogeneous features, leading to poor precision and low efficiency. To this end, we propose a plug-and-play module termed range-image fusion (RI-Fusion) to achieve an effective fusion of LiDAR and camera data, designed to be easily accessible by existing mainstream LiDAR-based algorithms. In this process, we design an image and point cloud alignment method by converting a point cloud into a compact range-view representation through a spherical coordinate transformation. The range image is then integrated with a corresponding camera image utilizing an attention mechanism. The original range image is then concatenated with fusion features to retain point cloud information, and the results are projected onto a spatial point cloud. Finally, the feature-enhanced point cloud can be input into a LiDAR-based 3D object detector. The results of validation experiments involving the KITTI 3D object detection benchmark showed that our proposed fusion method significantly enhanced multiple mainstream LiDAR-based 3D object detectors, PointPillars, SECOND, and Part $\text{A}{^{2}}$ , improving the 3D mAP (mean Average Precision) by 3.61%, 2.98%, and 1.27%, respectively, particularly for small objects such as pedestrians and cyclists.