# Research on Collision Warning Method for Ship-Bridge Based on Safety Potential Field
## 4 Vessel Warning for Bridge Area Based on Vessel Posture
### Real-Time Early Warning Method for the Safety Potential Field of a Bridge Area  
The static element potential energy and boundary fields form a fixed field due to their constant position, and can be used to determine the hazardous areas of the bridge area, i.e., areas inaccessible to ships. Through Kalman filtering and safety potential field modelling, the instantaneous integrated field strength value, \(E_{T}\), is calculated, and the integrated field strength \(E_{T+1}\) at the next moment is predicted. According to the comparison results of \(E_{T}\) and \(E_{T+1}\), the warning is divided into three levels, and different levels correspond to different warning signals, which suggests the possible dangers faced by the ship, so that timely collision avoidance measures can be taken to ensure the safety and effectiveness of navigation in the bridge area. The specific warning levels are as follows:  
1. \(E_{T+1}\leq E_{T}\) and \(E_{T+1}\in T_{1}\): \(T_{1}\) is the safe potential field range of the first level of warning, \(E_{T+1}\) is the predicted composite field strength at the next moment, and \(E_{T}\) is the superimposed field strength of the current ship position. If the predicted field strength is less than the current field strength, this indicates that the ship's navigation in the bridge area is safe and that there is no danger of hitting obstacles such as bridge abutments or the navigation channel. This is part of level 1 and is not dangerous;
2. \(E_{T+1}>E_{T}\) and \(E_{T+1}\in T_{2}\): \(T_{2}\) is the potential field range for a level 2 warning. Here, the predicted field strength is stronger than the current field strength, indicating that there is a possibility of the vessel impacting the bridge elements. However, as the predicted field strength is still within the \(T_{2}\) range, this indicates that the current situation in the bridge area has not yet reached the level of urgency and is classified as level 2, or a slight hazard;
3. \(E_{T+1}>E_{T}\) and \(E_{T+1}\in T_{3}\): \(T_{3}\) is the potential field range for a level 3 warning. Here, the predicted field strength value continues to increase and is within the range of a level 3 warning, indicating that the ship's danger to the bridge area is increasing and \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Pre-Longitude** & **Pre-Latitude** & **AIS-Longitude** & **AIS-Latitude** & **Error Longitude** & **Error Latitude** \\ \hline Straight-line navigation & 106.503861 & 29.437757 & 106.503847 & 29.4378 & 0.000014 & 0.000043 \\ Altering course & 106.500388 & 29.441710 & 106.50023 & 29.441663 & 0.000155 & 0.000047 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparative analysis of prediction errors between straight and altered course trajectories. Figure 10: Comparison between predicted and true speed of the vessel. has reached a degree of urgency that is of the third level, serious danger, as shown in Figure 11.  
The steps of the early warning algorithm are as follows:  
Step 1: Data collection: collect the environmental data and the real-time dynamic data of ships within 2 nautical miles and number each ship through a VTS, AIS and video monitoring system in the bridge area;  
Step 2: Take out the ship numbered i (i = 1,2,3,...\(N\)), calculate the field strength at the current moment based on the ship's current position information, heading information, and speed information, and predict the ship's movement position and speed after 2 min;  
Step 3: The predicted position, velocity, and other data are passed into a safe potential field model consisting of bridge zone elements;  
Step 4: Determine whether the integrated safety potential field exceeds the threshold by comprehensively evaluating all potential fields and determining whether the overall safety potential field exceeds the threshold;  
Step 5: Update cycle: As time passes (T = \(t\) + \(\Delta t\)), repeat steps 1 to 5 and continue to judge the next ship i + 1.