Compact Trip Representation over Networks

Abstract

We present a new Compact Trip Representation ($\mathsf {CTR}$) that allows us to manage users’ trips (moving objects) over networks. These could be public transportation networks (buses, subway, trains, and so on) where nodes are stations or stops, or road networks where nodes are intersections. $\mathsf {CTR}$ represents the sequences of nodes and time instants in users’ trips. The spatial component is handled with a data structure based on the well-known Compressed Suffix Array ($\mathsf {CSA}$), which provides both a compact representation and interesting indexing capabilities. We also represent the temporal component of the trips, that is, the time instants when users visit nodes in their trips. We create a sequence with these time instants, which are then self-indexed with a balanced Wavelet Matrix ($\mathsf {WM}$). This gives us the ability to solve range-interval queries efficiently. We show how $\mathsf {CTR}$ can solve relevant spatial and spatio-temporal queries over large sets of trajectories. Finally, we also provide experimental results to show the space requirements and query efficiency of $\mathsf {CTR}$.

Funded in part by European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 690941 (project BIRDS). N. Brisaboa, A. Fariña, and D. Galaktionov are funded by MINECO (PGE, CDTI, and FEDER) [TIN2013-46238-C4-3-R, TIN2013-47090-C3-3-P, TIN2015-69951-R, IDI-20141259, ITC-20151305, ITC-20151247]; by ICT COST Action IC1302; and by Xunta de Galicia (co-funded with FEDER) [GRC2013/053]. A. Rodríguez is funded by Fondecyt 1140428 and the Complex Engineering Systems Institute (CONICYT: FBO 16).