Mario A. Nascimento先生ご講演

2026年5月27日に，Mario A. Nascimento先生（Professor Emeritus, Department of Computing Science, University of Alberta）に，モバイルコンピューティングの授業で講演いただきました．

講演タイトル: Trajectory Imputation and Generation using Simple Probabilistic Language Models
概要: Trajectory data collected by GPS has found many critical applications. Unfortunately, most trajectory datasets have missing data due to technical problems or due to the sampling strategy used. Trajectory imputation is the task of filling in the gaps in actual trajectories by computing points that fit "naturally" within existing trajectories. Considering that both (discretized) trajectories and natural language are essentially sequences of symbols, we explore the use of probabilistic language models for trajectory imputation. Using a grid-based representation of the space, we convert trajectory points into tokens corresponding to the grid cell where they appear and train models of different sizes. We report experiments on a real dataset of over 500,000 taxi trips, showing that we can accurately fill gaps of up to 2km between GPS observations with 83% precision. These results are comparable to approaches using much more computationally demanding Large Language Models based on transformers. Time permitting, we will also show how the approach for trajectory imputation can be extended to generate arbitrarily large realistic trajectory datasets using real trajectory samples, which can then be used, for instance, for training machine learning models. (Research done in cooperation with Hayat Sultan Mohammed, Denilson Barbosa and Han Pai.)


Bio.: Mario Nascimento is currently an Emeritus Professor with the University of Alberta. Most recently he was with Northeastern University, serving as Khoury College of Computer Sciences’ inaugural Director of Pacific Northwest Research, based at the Vancouver Campus in Canada. Before that he was a Professor at the University of Alberta’s Department of Computing Science (including a six-year tenure as Department Chair). He has also been a visiting professor at the National University of Singapore’s School of Computing, Aalborg University’s Department of Computer Science in Denmark and Ludwig-Maximilians-Universität’s Institute for Informatics in Germany. His main research interests are in the area of spatiotemporal data management and, according to Google Scholar as of April/2026, his publications have been cited 5,200+ times, yielding an h-index of 35. He recently served as the General co-Chair for ACM SIGSPATIAL 2024, and as its Program Committee’s co-Chair in 2022 and 2023. He has also served often as a program committee member for the main database conferences, and served as GeoInformatica’s Editorial Board member (2017-2025) and SSTD’s Endowment’s director (2014-2025), VLDB Journal‘s Editorial Board member (2011-2017), ACM SIGMOD Record‘s Editor-In-Chief (2005-2007) and ACM SIGMOD‘s Information Director (2002-2005).