Existing vehicle re-identification methods commonly use spatial pooling
operations to aggregate feature maps extracted via off-the-shelf backbone
networks. They ignore exploring the spatial significance of feature maps,
eventually degrading the vehicle re-identification performance. In this paper,
firstly, an innovative spatial graph network (SGN) is proposed to elaborately
explore the spatial significance of feature maps. The SGN stacks multiple
spatial graphs (SGs). Each SG assigns feature map's elements as nodes and
utilizes spatial neighborhood relationships to determine edges among nodes.
During the SGN's propagation, each node and its spatial neighbors on an SG are
aggregated to the next SG. On the next SG, each aggregated node is re-weighted
with a learnable parameter to find the significance at the corresponding
location. Secondly, a novel pyramidal graph network (PGN) is designed to
comprehensively explore the spatial significance of feature maps at multiple
scales. The PGN organizes multiple SGNs in a pyramidal manner and makes each
SGN handles feature maps of a specific scale. Finally, a hybrid pyramidal graph
network (HPGN) is developed by embedding the PGN behind a ResNet-50 based
backbone network. Extensive experiments on three large scale vehicle databases
(i.e., VeRi776, VehicleID, and VeRi-Wild) demonstrate that the proposed HPGN is
superior to state-of-the-art vehicle re-identification approaches.

该论文提出了一种基于空间图注意力的新型车辆重新识别方法，它能够精确探索特征图的空间重要性，进而达到明显的性能提升。高效的网络设计可以使其适用于各种规模的特征图，并且在三个大规模数据库方面优于现有的车辆重新识别方法。