Abstract: With the further development of vessel location technology,a large amount of vessels trajectory data have been generated with the vessel positioning identification system installed on vessels.These compresseddata can improve the efficiency of data processing and applying to a large extent.However,compressing the vessel trajectory data online may have some problems such as high compression ratio and long time consuming.Therefore, this paper proposed a two-stage online compression algorithm (DTGO) which combines dynamic threshold value with global optimization.At the first stage,the original trajectory is processed in segments,and the threshold values are dynamically updated,thus a simplified trajectory can be obtained.At the second stage,the simplified trajectory is globally optimized by a modified SPM algorithm.Through the two-stage processing,the original trajectory is segmented into several sub-trajectory segments which are processed locally.Finally,the proposed global processing algorithm is applied to optimize all sub-trajectory segments globally.The experimental results show that the algorithm not only obtains higher compression efficiency,but also achieves better compression results.

Key words: AISvesseltrajectory, Dynamic thresholding, Global optimization, Online compression