With the wide availability of satellite, RFID, GPS, sensor, wireless, and video technologies, moving-object data have been collected in massive scale and are becoming increasingly rich, complex, and ubiquitous. There is an imminent need for scalable and flexible data analysis over moving-object information; and thus mining moving-object data has become one of major challenges in data mining. There have been considerable research efforts on data mining for moving object, trajectory, and traffic data sets.