GraphGST: Graph Generative Structure-Aware Transformer for Hyperspectral Image Classification

Transformer holds significance in deep learning (DL) research. Node embedding (NE) and positional encoding (PE) are usually two indispensable components in a Transformer. The former can excavate hidden correlations from the data, while the latter can store locational relationships between nodes. Recently, the Transformer has been applied for hyperspectral image (HSI) classification because the model can capture long-range dependencies to aggregate global features for representation learning. In an HSI, adjacent pixels tend to be homogeneous, while the NE does not identify the positional information of pixels. Therefore, PE is crucial for Transformers to understand locational relationships between pixels. However, in this area, most Transformer-based methods randomly generate PEs without considering their physical meaning, which leads to weak representations. This article proposes a new graph generative structure-aware Transformer (GraphGST) to solve the above-mentioned PE problem when implementing HSI classification. In our GraphGST, a new absolute PE (APE) is established to acquire pixels' absolute positional sequences (APSs) and is integrated into the Transformer architecture. Moreover, a generative mechanism with self-supervised learning is developed to achieve cross-view contrastive learning (CL), aiming to enhance the representation learning of the Transformer. The proposed GraphGST model can capture local-to-global correlations, and the extracted APSs can complement the spectral features of pixels to assist in NE. Several experiments with real HSIs are conducted to evaluate the effectiveness of our GraphGST. The proposed method demonstrates very competitive performance compared with other state-of-the-art (SOTA) approaches. Our source codes will be provided in the following link https://github.com/yuanchaosu/TGRS-graphGST.