Figure 1.
A running example of ship trajectory.
Figure 1.
A running example of ship trajectory.
Figure 2.
Examples of trajectory with a low-speed point. The gray box in the figure includes three trajectory points that are at small distances from each other, but the difference in direction of the trajectory segments is large.
Figure 2.
Examples of trajectory with a low-speed point. The gray box in the figure includes three trajectory points that are at small distances from each other, but the difference in direction of the trajectory segments is large.
Figure 3.
Illustration of the speed error between the original speed and speed from interpolation. The black dots represent the ship’s speeds at the corresponding moments, and the red line represents the linear change of the speed from the starting point to the end point, after compress the trajectory, we can find the ship’s speeds at through the linear interpolation(the white circle on the red line). The speed error at is .
Figure 3.
Illustration of the speed error between the original speed and speed from interpolation. The black dots represent the ship’s speeds at the corresponding moments, and the red line represents the linear change of the speed from the starting point to the end point, after compress the trajectory, we can find the ship’s speeds at through the linear interpolation(the white circle on the red line). The speed error at is .
Figure 4.
Reception interval statistics for neighboring AIS track points.
Figure 4.
Reception interval statistics for neighboring AIS track points.
Figure 5.
Statistical results of the speed distribution in port waters. (a) Frequency distribution chart of the different speeds. (b) Cumulative frequency distribution chart of the different speeds.
Figure 5.
Statistical results of the speed distribution in port waters. (a) Frequency distribution chart of the different speeds. (b) Cumulative frequency distribution chart of the different speeds.
Figure 6.
Statistical results of the speed distribution in coastal waters. (a) Frequency distribution chart of the different speeds. (b) Cumulative frequency distribution chart of the different speeds.
Figure 6.
Statistical results of the speed distribution in coastal waters. (a) Frequency distribution chart of the different speeds. (b) Cumulative frequency distribution chart of the different speeds.
Figure 7.
Theoretical schematic of the radial distance method to deal with the low-speed AIS trajectory points. In (a), the distance from , to are less than , so these two points are deleted. In (b), is the key point, and no points were deleted. In (c), is the key point, and the distance from is less than , so is deleted. In (d), after the radial distance method, the remaining points were .
Figure 7.
Theoretical schematic of the radial distance method to deal with the low-speed AIS trajectory points. In (a), the distance from , to are less than , so these two points are deleted. In (b), is the key point, and no points were deleted. In (c), is the key point, and the distance from is less than , so is deleted. In (d), after the radial distance method, the remaining points were .
Figure 8.
Theoretical schematic of the Open Window method to compress the AIS trajectory based on directional threshold.
Figure 8.
Theoretical schematic of the Open Window method to compress the AIS trajectory based on directional threshold.
Figure 9.
The area where the experimental data are located. (a) The coastal waters in eastern Zhejiang. (b) The port area at Yingkou Ports.
Figure 9.
The area where the experimental data are located. (a) The coastal waters in eastern Zhejiang. (b) The port area at Yingkou Ports.
Figure 10.
Comparison of the compression rate between the proposed method (DPTSM) and the DPTS method with the same tolerance. (a) Comparison of the rate in port waters. (b) Comparison of the rate in coast waters.
Figure 10.
Comparison of the compression rate between the proposed method (DPTSM) and the DPTS method with the same tolerance. (a) Comparison of the rate in port waters. (b) Comparison of the rate in coast waters.
Figure 11.
Comparison of the running time between the proposed method (DPTSM) and the DPTS method with the same tolerance. (a) Comparison of the running time in port waters. (b) Comparison of the running time in coast waters.
Figure 11.
Comparison of the running time between the proposed method (DPTSM) and the DPTS method with the same tolerance. (a) Comparison of the running time in port waters. (b) Comparison of the running time in coast waters.
Figure 12.
Comparison of the running time between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the running time in port waters. (b) Comparison of the running time in coast waters.
Figure 12.
Comparison of the running time between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the running time in port waters. (b) Comparison of the running time in coast waters.
Figure 13.
Comparison of the running time between the proposed method (DPTSM) and the DP method with the same compression rate (95%) for different data sizes. (a) Comparison of the running time in port waters. (b) Comparison of the running time in coast waters.
Figure 13.
Comparison of the running time between the proposed method (DPTSM) and the DP method with the same compression rate (95%) for different data sizes. (a) Comparison of the running time in port waters. (b) Comparison of the running time in coast waters.
Figure 14.
Comparison of the average position error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the average position error in port waters. (b) Comparison of the average position error in coast waters.
Figure 14.
Comparison of the average position error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the average position error in port waters. (b) Comparison of the average position error in coast waters.
Figure 15.
Comparison of the max position error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the max position error in port waters. (b) Comparison of the max position error in coast waters.
Figure 15.
Comparison of the max position error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the max position error in port waters. (b) Comparison of the max position error in coast waters.
Figure 16.
Comparison of the average speed error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the average speed error in port waters. (b) Comparison of the average speed error in coast waters.
Figure 16.
Comparison of the average speed error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the average speed error in port waters. (b) Comparison of the average speed error in coast waters.
Figure 17.
Comparison of the max speed error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the max speed error in port waters. (b) Comparison of the max speed error in coast waters.
Figure 17.
Comparison of the max speed error between the proposed method (DPTSM), the DPTS method, and the DP method with the same compression rate. (a) Comparison of the max speed error in port waters. (b) Comparison of the max speed error in coast waters.
Figure 18.
Visual analysis of the port water datasets. (a) is AIS trajectory after compression (b) is AIS trajectory before compression.
Figure 18.
Visual analysis of the port water datasets. (a) is AIS trajectory after compression (b) is AIS trajectory before compression.
Figure 19.
Visual analysis of the coastal water datasets. (a) is AIS trajectory after compression (b) is AIS trajectory before compression.
Figure 19.
Visual analysis of the coastal water datasets. (a) is AIS trajectory after compression (b) is AIS trajectory before compression.
Table 1.
Class A ship-borne mobile equipment reporting intervals.
Table 1.
Class A ship-borne mobile equipment reporting intervals.
Ship Dynamic Conditions | Nominal Reporting Interval |
---|
Ship at anchor or moored and not moving faster than 3 knots | 3 min |
Ship at anchor or moored and moving faster than 3 knots | 10 s |
Ship 0–14 knots | 10 s |
Ship 0–14 knots and changing course | 3 1/3 s |
Ship 14–23 knots | 6 s |
Ship 14–23 knots and changing course | 2 s |
Ship > 23 knots | 2 s |
Ship > 23 knots and changing course | 2 s |
Table 2.
The datasets used in our experiments.
Table 2.
The datasets used in our experiments.
| # of Ships | Total # of Positions | Average # of Positions Per Trajectory | The Range of Time Periods |
---|
Port waters | 274 | 1,154,259 | 4212.624 | 1–3 June 2020 |
Coastal waters | 759 | 1,175,585 | 1548.86 | 1 May 2021 |
Table 3.
The results of the compression rate by the proposed algorithm and DPTS.
Table 3.
The results of the compression rate by the proposed algorithm and DPTS.
Tolerance | Port Water Datasets | Coastal Water Datasets |
---|
Proposed (%) | DPTS (%) | Proposed (%) | DPTS (%) |
---|
0.01 | 74.9624 | 43.6223 | 58.3782 | 43.7457 |
0.02 | 80.862 | 49.8946 | 74.2668 | 59.7033 |
0.03 | 84.3227 | 53.7386 | 82.6386 | 68.1655 |
0.04 | 86.6007 | 56.3758 | 87.4004 | 73.0338 |
0.05 | 88.144 | 58.2332 | 90.2434 | 75.9777 |
0.06 | 89.2624 | 59.6631 | 92.0444 | 77.8844 |
0.07 | 90.1543 | 60.9131 | 93.2495 | 79.1873 |
0.08 | 90.8524 | 61.8728 | 94.1027 | 80.1729 |
0.09 | 91.4385 | 62.7361 | 94.7348 | 80.9376 |
0.1 | 91.9387 | 63.5255 | 95.201 | 81.4949 |
0.2 | 94.5103 | 68.5503 | 97.1415 | 84.5426 |
0.3 | 95.512 | 71.4195 | 97.6818 | 86.09 |
0.4 | 96.0154 | 73.5526 | 97.9239 | 87.0783 |
0.5 | 96.328 | 75.1678 | 98.0795 | 88.0374 |