In this paper, we propose a new image-based visual place recognition (VPR)
framework by exploiting the structural cues in bird's-eye view (BEV) from a
single monocular camera. The motivation arises from two key observations about
VPR: 1) For the methods based on both camera and LiDAR sensors, the integration
of LiDAR in robotic systems has led to increased expenses, while the alignment
of data between different sensors is also a major challenge. 2) Other
image-/camera-based methods, involving integrating RGB images and their derived
variants (e.g., pseudo depth images, pseudo 3D point clouds), exhibit several
limitations, such as the failure to effectively exploit the explicit spatial
relationships between different objects. To tackle the above issues, we design
a new BEV-enhanced VPR framework, nemely BEV2PR, which can generate a composite
descriptor with both visual cues and spatial awareness solely based on a single
camera. For the visual cues, any popular aggregation module for RGB global
features can be integrated into our framework. The key points lie in: 1) We use
BEV segmentation features as an explicit source of structural knowledge in
constructing global features. 2) The lower layers of the pre-trained backbone
from BEV map generation are shared for visual and structural streams in VPR,
facilitating the learning of fine-grained local features in the visual stream.
3) The complementary visual features and structural features can jointly
enhance VPR performance. Our BEV2PR framework enables consistent performance
improvements over several popular camera-based VPR aggregation modules when
integrating them. The experiments on our collected VPR-NuScenes dataset
demonstrate an absolute gain of 2.47% on Recall@1 for the strong Conv-AP
baseline to achieve the best performance in our setting, and notably, a 18.06%
gain on the hard set.

通过利用鸟瞰视角中的结构线索，我们提出了一种新的基于图像的视觉位置识别（VPR）框架。该框架能够仅基于单个摄像头生成具有视觉线索和空间感知的复合描述符。在我们收集的 VPR-NuScenes 数据集上的实验证明，与其他常用的基于相机的 VPR 聚合模块相比，我们的 BEV2PR 框架在 Recall@1 上取得了 2.47% 的绝对增益，并在难样本上取得了 18.06% 的增益。