LidaRefer: Outdoor 3D Visual Grounding for Autonomous Driving with Transformers

3D visual grounding (VG) aims to locate relevant objects or regions within 3D scenes based on natural language descriptions. Although recent methods for indoor 3D VG have successfully transformer-based architectures to capture global contextual information and enable fine-grained cross-modal fusion, they are unsuitable for outdoor environments due to differences in the distribution of point clouds between indoor and outdoor settings. Specifically, first, extensive LiDAR point clouds demand unacceptable computational and memory resources within transformers due to the high-dimensional visual features. Second, dominant background points and empty spaces in sparse LiDAR point clouds complicate cross-modal fusion owing to their irrelevant visual information. To address these challenges, we propose LidaRefer, a transformer-based 3D VG framework designed for large-scale outdoor scenes. Moreover, during training, we introduce a simple and effective localization method, which supervises the decoder's queries to localize not only a target object but also ambiguous objects that might be confused as the target due to the exhibition of similar attributes in a scene or the incorrect understanding of a language description. This supervision enhances the model's ability to distinguish ambiguous objects from a target by learning the differences in their spatial relationships and attributes. LidaRefer achieves state-of-the-art performance on Talk2Car-3D, a 3D VG dataset for autonomous driving, with significant improvements under various evaluation settings.