SAANet: Spatial adaptive alignment network for object detection in automatic driving

Abstract

Both images and point clouds are beneficial for object detection in a visual navigation module for autonomous driving. The spatial relationships between different objects at different times in a bimodal space can vary significantly. It is difficult to combine bimodal descriptions into a unified model to effectively detect objects in an efficient amount of time. In addition, conventional voxelization methods resolve point clouds into voxels at a global level, and often overlook local attributes of the voxels. To address these problems, we propose a novel fusion-based deep framework named SAANet. SAANet utilizes a spatial adaptive alignment (SAA) module to align point cloud features and image features, by automatically discovering the complementary information between point clouds and images. Specifically, we transform the point clouds into 3D voxels, and introduce local orientation encoding to represent the point clouds. Then, we use a sparse convolutional neural network to learn a point cloud feature. Simultaneously, a ResNet-like 2D convolutional neural network is used to extract an image feature. Next, the point cloud feature and image feature are fused by our SAA block to derive a comprehensive feature. Then, the labels and 3D boxes for objects are learned using a multi-task learning network. Finally, an experimental evaluation on the KITTI benchmark demonstrates the advantages of our method in terms of average precision and inference time, as compared to previous state-of-the-art results for 3D object detection.