PointDMIG: a dynamic motion-informed graph neural network for 3D action recognition

Point cloud contains rich spatial information, providing effective supplementary clues for action recognition. Existing action recognition algorithms based on point cloud sequences typically employ complex spatiotemporal local encoding to capture the spatiotemporal features, leading to the loss of spatial information and the inability to establish long-term spatial correlation. In this paper, we propose a PointDMIG network that models the long-term spatio-temporal correlation in point cloud sequences while retaining spatial structure information. Specifically, we first employ graph-based static point cloud techniques to construct topological structures for input point cloud sequences and encodes them as human static appearance feature vectors, introducing inherent frame-level parallelism to avoid the loss of spatial information. Then, we extend the technique for static point clouds by integrating the motion information of points between adjacent frames into the topological graph structure, capturing the long-term spatio-temporal evolution of human static appearance while preserving its spatial structure. Moreover, in order to enhance the semantic representation of the point cloud sequences, PointDMIG reconstructs the downsampled point set in the feature extraction process, further enriching the spatio-temporal information of human body movements. Experimental results on NTU RGB+D 60 and MSR Action 3D show that PointDMIG significantly improves the accuracy of 3D human action recognition based on point cloud sequences. We also performed an extended experiment on gesture recognition on the SHREC 2017 dataset, and PointDMIG achieved competitive results.