Distance Threshold Similarity Searches: Efficient Trajectory Indexing on the GPU.

Applications in many domains perform searches over datasets that contain moving object trajectories. A common class of searches are similarity searches that attempt to identify trajectories with similar characteristics. In this work, we focus on the distance threshold similarity search that finds all trajectories within a given distance of a query trajectory over a time interval. This search involves large numbers of Euclidean moving distance calculations, thus making it a good candidate for execution on manycore platforms such as GPUs. However, low search response time is preconditioned on efficient indexing of trajectory data. We propose three indexing schemes designed for the GPU, with spatial, temporal and spatiotemporal selectivity. These schemes differ significantly from traditional tree-based indexing schemes that have been previously proposed for CPU executions. We evaluate implementations of our proposed indexing schemes using two synthetic and one real-world astrophysics dataset, showing under which conditions each scheme achieves high performance. Our broad finding is that a GPU implementation, provided an appropriate indexing scheme is used, can outperform a multithreaded CPU implementation that uses a state-of-the-art index tree. In particular, the performance improvement is large for regimes that are relevant for classes of real-world applications, thereby demonstrating that the GPU is an attractive platform for searching and processing moving object trajectories.