Skeleton-based Relational Reasoning for Group Activity Analysis.

Research on group activity recognition mostly leans on standard two-stream approach (RGB and Optical Flow) as their input features. Few have explored explicit pose information, with none using it directly to reason about the individuals interactions. In this paper, we leverage the skeleton information to learn the interactions between the individuals straight from it. With our proposed method GIRN, multiple relationship types are inferred from independent modules, that describe the relations between the joints pair-by-pair. Additionally to the joints relations, we also experiment with previously unexplored relationship between individuals and relevant objects (e.g. volleyball). The individuals distinct relations are then merged through an attention mechanism, that gives more importance to those more relevant for distinguishing the group activity. We evaluate our method in the Volleyball dataset, obtaining competitive results to the state-of-the-art, even though using a single modality. Therefore demonstrating the potential of skeleton-based approaches for modeling multi-person interactions.