Abstract: Ship track compressing is an important step in global ship trace big data processing.This paper firstly expounded some existing offline compression algorithms for ship trajectory and also exhibited their problems.For example,classic Douglas-Peucker compression algorithm just compresses the ship trajectory in two dimensions,losing time element,which makes that the compression algorithm cannot keep the information of speed and status of ships.On the other hand,although dynamic Douglas-Peucker compression algorithm needs to divide ship trajectory into different groups before compression,it will yet result in some efficiency problems.The compression algorithms which takes into account time dimensions was token to spatial vector.In order to improve the effect and efficiency,we used inner product and outer product.Through experiment,we found that the efficiency of the algorithm had a 30% increase and a better effect in most cases.The innovation is putting the inner product and outer product into compression algorithms.

Key words: Ship trajectory,Automatic identification system (AIS),Trajectory compression,Space-Time sequence,Douglas-Puke algorithm