Ship AIS trajectory extrapolation method based on state constraints

Abstract

The present invention discloses a ship AIS trajectory extrapolation method based on state constraints, comprising the following steps: S1: establishing a ship AIS trajectory extrapolation model; S2: obtaining basic information of the ship and the ship's AIS information; S3: constraining the ship's AIS trajectory based on the basic information of the ship and setting a constraint range for the ship AIS trajectory extrapolation; S4: estimating the ship's position, speed, acceleration, turning rate, and turning acceleration at future moments using the ship AIS trajectory extrapolation model based on the ship's AIS information and the constraint range for the ship's AIS trajectory extrapolation. Based on the rule that the ship's motion acceleration automatically decays over time, the present invention utilizes the ship's static information, ship type and size, route history information, ship encounter maneuvering rules, verifies the ship's historical motion parameters, estimates the ship's inertia and maneuverability, and estimates the ship's motion trajectory, thereby more accurately fitting the ship's motion trajectory.

Description

Technical Field

[0001] The present invention relates to a ship AIS trajectory extrapolation method, in particular to a ship AIS trajectory extrapolation method based on state constraints. Background Art

[0002] AIS plays an important role in ship traffic management and is also widely used in ship safety supervision in the fishery and water tourism industries.

[0003] Video surveillance can provide the most direct, real-time on-site information for safety supervision in various industries and is a crucial source of information for situational awareness and command and control. To strengthen vessel supervision, it is often necessary to use AIS information to guide cameras to continuously track and monitor vessels across multiple cameras.

[0004] The actual situation that the time interval for position reporting of ships equipped with Class B AIS terminals may be as long as 30 seconds often leads to the inability to achieve continuous tracking when the ship is maneuvering, especially when the ship is turning and maneuvering, there is a high possibility of losing the target.

[0005] Conventional AIS track extrapolation methods are mainly linear extrapolation, which is based on the assumption that the target moves in a uniform straight line. Therefore, the track prediction error under ship turning and maneuvering conditions is large and cannot be effectively applied to video linkage tracking of ships.

[0006] In the management of ships involved in water, it is often impossible to identify the names of ships seen in video images, so the ship's attribute information (ship name, length, ship width, draft, etc.) cannot be grasped. If there is an intelligent video annotation function, the AIS information of ships with AIS can be automatically annotated, and the AIS information can be used to automatically query the ship database to obtain detailed ship attribute information, which will improve the efficiency of video supervision in the field of ship management. This application scenario has higher requirements for AIS target track calculation. Only with a relatively accurate extrapolated track can the AIS track and the optical tracking target be associated with the track, or the AIS track can be directly transformed into the field of view of video monitoring. Therefore, it is necessary to provide a ship AIS track extrapolation method based on state constraints to achieve accurate calculation of the ship track. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a ship AIS track extrapolation method based on state constraints, which solves the problem that the existing AIS track extrapolation method has a large track prediction error under ship turning maneuvering conditions and cannot accurately calculate the ship track.

[0008] The technical solution adopted by the present invention to solve the above technical problems is to provide a ship AIS trajectory extrapolation method based on state constraints, comprising the following steps: S1: establishing a ship AIS trajectory extrapolation model; S2: obtaining basic information of the ship and the ship's AIS information; the basic information of the ship includes the ship's type, size, current navigation status, currently applicable channel information, and currently applicable collision avoidance regulations; the AIS information of the ship includes the ship's current AIS information and historical AIS information, and the AIS information includes the ship's position, speed, heading, and turning rate information; S3: constraining the ship's AIS trajectory based on the basic information of the ship, and setting a constraint range for the ship's AIS trajectory extrapolation; S4: estimating the ship's position, speed, acceleration, turning rate, and turning acceleration at future times through the ship's AIS trajectory extrapolation model based on the ship's AIS information and the constraint range for the ship's AIS trajectory extrapolation.

[0009] Furthermore, in step S1, a ship AIS trajectory extrapolation model is established based on the automatic decay of the ship's motion acceleration over time; the calculation formulas for the various parameters in the ship AIS trajectory extrapolation model are as follows:

[0010] D h =V n (t h -t n )+∫∫Av t n ≤t≤t h

[0011] θ h =R n (t h -t n )+∫∫Ar t n ≤t≤t h

[0012] Where:

[0013] V n =S n / (t n -t n-1 )

[0014] R n =γ n / (t n -t n-1 )

[0015] Av=Av n (1-(1 / K)*t)+E av t n +0.0≤t≤t n +K

[0016] Av=0.0tn +K<t≤t h

[0017] Ar is a piecewise function, the first part is the function of the first M seconds, and the second part is the function after M seconds;

[0018] Ar=Ar n (1-1 / M*t) t n +0.0≤t≤t n +M

[0019] Ar=R k / N+E ar t n +M<t≤t n +M+N

[0020] Ar=0.0 t n +M+N<t≤t h

[0021] In the piecewise function of Ar,

[0022] Ar n =(R n -R n-1 ) / (t n -t n-1 ) t n +0.0≤t≤t n +M

[0023] R k =R n +∫Ar t n +0.0≤t≤t n +M

[0024] Where Av: acceleration function; Ar: steering acceleration function; t n : The measurement time of the latest position measurement point, that is, P n UTC time of the point; t n-1 : The measurement time of the last position measurement point, that is, P n-1 UTC time of the point; t h : predicted time of the predicted location point; D h :Predicted location point and P n The estimated value of the distance change of the location point; θ h :Predicted location point and P n Estimated value of heading change at the position point; V n : The speed of the latest position measurement point, that is, P n The speed of the point; V n-1 : The speed of the last position measurement point, that is, P n-1 The speed of the point; R n: The turning speed (turn rate) of the latest position measurement point, that is, P n The turning speed of the point; R n-1 : The turning speed (turn rate) of the last position measurement point, that is, P n-1 Turning speed of point; S n : Track point P n To track point P n-1 The distance difference; γ n : Track point P n To track point P n-1 The distance and heading angle difference; Av n : The acceleration of the latest position measurement point, that is, P n Acceleration of a point; Av n-1 : The acceleration of the last position measurement point, that is, P n-1 Acceleration of point; Ar n : The steering acceleration of the latest position measurement point, that is, P n Turning acceleration of point; Ar n-1 : The steering acceleration of the last position measurement point, that is, P n-1 The turning acceleration of the point; E av : acceleration error correction; E ar : Steering acceleration error correction; K: The time it takes for the set ship acceleration to be reduced to 0; M: The time it takes for the set ship steering acceleration to be reduced to 0; N: The time it takes for the set ship steering speed to be reduced to 0.

[0025] Furthermore, the acceleration error correction value E av and steering acceleration error correction E ar The calculation formula is as follows:

[0026] E av =E v / Ta

[0027] E ar =E r / Tr

[0028] Where, E v : average velocity error; Ta: the time it takes for the acceleration to decay to 0; E r : average steering rate error; Tr: time taken for the steering acceleration to decay to 0.

[0029] Where, the average speed error E v and the average turning rate error E r The calculation formula is as follows:

[0030] E v =E d / (t n -t n-1)

[0031] E r =E c / (t n -t n-1 )

[0032] Where, E d : range error; E c : heading error; t n : The measurement time of the current position measurement point, that is, P n UTC time of the point; t n-1 : The measurement time of the previous position measurement point, that is, P n-1 The UTC time of the point.

[0033] Furthermore, in step S3, the AIS trajectory of the ship is constrained according to the type and size of the ship, including setting the value of the constraint parameter K in the Av function, setting K = 5s for small ships, K = 15s for small, medium and unknown type ships, K = 30s for medium ships, and K = 60s for large ships.

[0034] Furthermore, in step S3, the ship AIS trajectory is constrained according to the current navigation status, channel information, and channel collision avoidance rules, including the following steps:

[0035] S31: Constraining the vessel's navigation position using currently applicable channel information; the channel information includes digital channel information generated by electronic nautical charts or electronic river charts and empirical channel data generated by a large amount of AIS historical track data;

[0036] S32: constraining the ship's navigation speed, acceleration, turning rate and turning acceleration according to the current navigation status and the currently applicable collision avoidance rules;

[0037] S33: By adjusting the values ​​of the constraint parameters K, M and N in the Ar function, the position, speed, acceleration, turning rate and turning acceleration of the ship's navigation are adjusted.

[0038] Furthermore, the navigation state includes three states of encounter between two ships, namely, a head-on encounter state, a crossing encounter state, and an overtaking state. Step S32 includes: predicting the actions and maneuvering intentions of the ships according to the navigation state in accordance with the collision avoidance rules, and constraining the speed, acceleration, turning rate, and steering acceleration in the track extrapolation model according to the predicted maneuvering intentions of the ships.

[0039] Furthermore, the step S4 includes: S41: determining the values ​​of the constraint parameters K, M and N according to the constraint range of the ship AIS trajectory extrapolation; S42: obtaining the error parameter average speed error E of the previous reporting period v and the average turning rate error Er , calculate the acceleration error correction E av and steering acceleration error correction E ar ; Initialize the parameters of the Av function; S43: Iterate S n-1 , γ n-1 、V n-1 、R n-1 、Av n-1 , solve for S n , γ n 、V n 、R n 、Av n 、Ar n ; S44: Calculate Av function, calculate Av at t n to t h Double integral of t; S45: Calculate t n to t n +M interval Ar function, calculate Ar at t n to t n +M integral, calculate t n +M to t h Ar function of the interval, calculate Ar at t n to t h Double integral of; S46: Calculate the distance and azimuth change D h ,θ h , calculate t h The latitude and longitude at the moment.

[0040] Furthermore, step S4 also includes calculating the error parameters of this reporting period, the steps are as follows: S51: obtaining the estimated position at the time of this report; S52: calculating the range error E according to the position, speed, heading and turning rate of the AIS information of this reporting period d and heading error E c ; S53: According to the cycle of this report, calculate and save the error parameters of this report cycle, including the average speed error E v and the average turning rate error E r .

[0041] Furthermore, in step S2, the current AIS information is obtained from the AIS message received by the ship's AIS terminal, and the historical AIS information is obtained from the ship's AIS historical track database.

[0042] Compared with the existing technology, the present invention has the following beneficial effects: the state-constrained ship AIS trajectory extrapolation method provided by the present invention is based on the rule that the ship's motion acceleration automatically decays over time, utilizes the ship's static information, ship type, size, etc., route history information, ship encounter maneuvering rules, verifies the ship's historical motion parameters, estimates the ship's inertia and maneuverability, and estimates the ship's motion trajectory, thereby more accurately fitting the ship's motion trajectory. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Flowchart of a method for extrapolating ship AIS trajectory based on state constraints in an embodiment of the present invention;

[0044] Figure 2 Schematic diagram of extrapolation of a Class A AIS terminal in an embodiment of the present invention;

[0045] Figure 3 Schematic diagram of extrapolation of a Class B AIS terminal in an embodiment of the present invention;

[0046] Figure 4 Schematic diagram of three types of encounters between two ships in an embodiment of the present invention;

[0047] Figure 5 Schematic diagram of an avoidance action of two ships meeting each other on the port side in an embodiment of the present invention;

[0048] Figure 6 Schematic diagram of the avoidance action of two ships crossing at a small angle in an embodiment of the present invention;

[0049] Figure 7 This is a schematic diagram of an overtaking action in an embodiment of the present invention;

[0050] Figure 8 This is a flow chart of ship track extrapolation calculation in an embodiment of the present invention;

[0051] Figure 9 This is a flow chart of track extrapolation error calculation in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below with reference to the accompanying drawings and examples.

[0053] Figure 1 Schematic diagram of the structure of the ship AIS trajectory extrapolation method based on state constraints in an embodiment of the present invention.

[0054] See Figure 1 The ship AIS trajectory extrapolation method based on state constraints according to an embodiment of the present invention includes the following steps:

[0055] S1: Establish a ship AIS trajectory extrapolation model;

[0056] S2: Obtain basic information of the ship and the ship's AIS information; the basic information of the ship includes the ship's type, size, current navigation status, currently applicable channel information, and currently applicable collision avoidance regulations; the AIS information of the ship includes the ship's current AIS information and historical AIS information, and the AIS information includes the ship's position, speed, heading, and turning rate information;

[0057] S3: Constrain the ship's AIS trajectory based on the ship's basic information and set the constraint range for the ship's AIS trajectory extrapolation;

[0058] S4: Based on the ship's AIS information and the constraints of the ship's AIS trajectory extrapolation, the ship's position, speed, acceleration, turning rate, and turning acceleration at future moments are estimated through the ship's AIS trajectory extrapolation model.

[0059] Specifically, in step S1, a ship AIS trajectory extrapolation model is established based on the automatic decay of the ship's motion acceleration over time; due to the following characteristics of ship motion:

[0060] A ship is an inertial body, constrained by the natural resistance of its motion space (water, atmosphere), and its speed and direction cannot change suddenly. Therefore, the first-order derivative of the ship's trajectory at the point of the most recent AIS position report exists and is continuously differentiable.

[0061] Due to the immense inertia of a ship's propeller shaft, the propeller's rotational speed cannot change suddenly, and therefore the thrust it generates cannot change suddenly. Adding to this the natural resistance of the space in which it moves (water, atmosphere), wind, and current forces, the combined force acting on the ship cannot change suddenly either. According to the equation F = ma, the ship's acceleration cannot change suddenly either. The second-order derivative of the ship's trajectory exists and is continuously differentiable at the point of the most recent AIS position report.

[0062] When the propulsion power is insufficient or absent, the ship decelerates due to natural resistance (water and atmosphere). Water and atmosphere, acting as damping media, exert resistance proportional to the ship's speed: the higher the speed, the greater the resistance. Consequently, the acceleration during natural deceleration exhibits a decreasing pattern, decaying over time. Different ship types have varying inertia and maneuverability, resulting in different acceleration decay parameters.

[0063] The position, speed, heading, and rate of turn information reported by AIS is a sample of the ship's motion trajectory at the time of reporting. The sample value of this sample describes the tangent slope (speed and heading) and curve curvature (rate of turn) of the ship's motion trajectory at the time of the AIS report.

[0064] Based on the aforementioned ship motion characteristics, a ship trajectory can be fitted using AIS information (position, speed, heading, and rate of turn). The parameters of the fitted trajectory can then be used to extrapolate the ship's likely position over a period of time. During track extrapolation, the parameters of the fitted curve are used to estimate the speed and acceleration, rate of turn, and rate of turn acceleration at future moments.

[0065] Therefore, the calculation formulas for the parameters in the ship AIS trajectory extrapolation model are as follows:

[0066] D h =V n (t h -t n )+∫∫Av t n ≤t≤t h

[0067] θ h =R n (t h -t n )+∫∫Ar t n ≤t≤t h

[0068] Where:

[0069] V n =S n / (t n -t n-1 )

[0070] R n =γ n / (t n -t n-1 )

[0071] Av=Av n (1-(1 / K)*t)+E av t n +0.0≤t≤t n +K

[0072] Av=0.0t n +K<t≤t h

[0073] Ar is a piecewise function, the first part is the function of the first M seconds, and the second part is the function after M seconds;

[0074] Ar=Ar n (1-1 / M*t) t n +0.0≤t≤t n +M

[0075] Ar=R k / N+E art n +M<t≤t n +M+N

[0076] Ar=0.0 t n +M+N<t≤t h

[0077] In the piecewise function of Ar,

[0078] Ar n =(R n -R n-1 ) / (t n -t n-1 ) t n +0.0≤t≤t n +M

[0079] R k =R n +∫Ar t n +0.0≤t≤t n +M

[0080] in,

[0081] Av: acceleration function;

[0082] Ar: steering acceleration function;

[0083] t n : The measurement time of the latest position measurement point, that is, P n The UTC time of the point;

[0084] t n-1 : The measurement time of the last position measurement point, that is, P n-1 UTC time of the point;

[0085] t h : The predicted time of the predicted location point;

[0086] D h :Predicted location point and P n The estimated distance change of the location point;

[0087] θ h :Predicted location point and P n Estimated heading change of the position point;

[0088] V n : The speed of the latest position measurement point, that is, P n The speed of the point;

[0089] V n-1 : The speed of the last position measurement point, that is, P n-1 The speed of the point;

[0090] R n : The turning speed (turn rate) of the latest position measurement point, that is, P n The turning speed of the point;

[0091] R n-1 : The turning speed (turn rate) of the last position measurement point, that is, P n-1 The turning speed of the point;

[0092] S n : Track point P n To track point P n-1 The distance difference;

[0093] γ n : Track point P n To track point P n-1 The distance and heading angle difference;

[0094] Av n : The acceleration of the latest position measurement point, that is, P n The acceleration of the point;

[0095] Av n-1 : The acceleration of the last position measurement point, that is, P n-1 The acceleration of a point;

[0096] Ar n : The steering acceleration of the latest position measurement point, that is, P n The turning acceleration of the point;

[0097] Ar n-1 : The steering acceleration of the last position measurement point, that is, P n-1 The turning acceleration of the point;

[0098] E av : acceleration error correction;

[0099] E ar : Steering acceleration error correction;

[0100] K: The time it takes for the ship's acceleration to decrease to 0;

[0101] M: The time it takes for the ship's steering acceleration to decrease to 0;

[0102] N: The time it takes for the ship's turning speed to decrease to 0.

[0103] Specifically, the acceleration error correction amount E av and steering acceleration error correction E ar The calculation formula is as follows:

[0104] E av =Ev / Ta

[0105] E ar =E r / Tr

[0106] Where, E v : average velocity error; Ta: the time it takes for the acceleration to decay to 0; E r : average steering rate error; Tr: time taken for the steering acceleration to decay to 0.

[0107] AIS terminals installed on ships are categorized into Class A and Class B. Class A terminals report relatively good information integrity and a high frequency of position data reporting. Class B terminals, on the other hand, report less frequently and also report significantly less complete information. Therefore, different error correction methods are required to account for the varying integrity of AIS information from different ships.

[0108] See Figure 2 , the ship AIS trajectory extrapolation method based on state constraints in the embodiment of the present invention, the ship uses a Class A AIS terminal, P n (n=0, 1, 2, ..., ∞) is the ship position at time n reported by AIS, R n (n=0, 1, 2, ..., ∞) is the turning rate at time n reported by the AIS, H n (n=0、1、2、...、∞) is the P at time n n 、R n and historical information (P n-1 、P n-2 、P n-3 ,...; R n-1 、R n-2 、R n-3 , ...), and perform multi-hypothesis track extrapolation to calculate the position point. n The calculation is applicable to P n Afterwards n+1 Dead reckoning of position at any time during the previous time period. n The calculation method is as follows:

[0109] H0: Estimates H0's speed from P0's. Calculates H0's direction and rate of turn from P0's heading and rate of turn. If P0's rate of turn is not zero, the calculation is based on a 30-second reduction to zero rudder angle, assuming the rudder returns to zero within 30 seconds.

[0110] H1: Calculate the speed and acceleration based on the position and speed differences between P0 and P1. If the acceleration is non-zero, the acceleration is calculated based on the vessel type, taking 5 seconds (small), 15 seconds (small, medium, and unknown), 30 seconds (medium), and 60 seconds (large) and then reduced to zero. This allows the speed of H1 to be estimated. The turning rate and turning acceleration are calculated based on the turning rate difference between P0 and P1. If the turning acceleration is greater than 0, the turning acceleration is calculated based on 2 seconds and then reduced to 0. When the turning acceleration is 0, if the turning rate is non-zero, the turning rate is calculated based on 15 seconds and then reduced to 0. This allows the direction and turning rate of H1 to be estimated.

[0111] H2: Calculate the velocity and acceleration based on the position and velocity differences between adjacent points P0, P1, and P2. If the acceleration is non-zero, the acceleration is calculated based on the vessel type, with a time interval of 5 seconds (small), 15 seconds (small, medium, and unknown), 30 seconds (medium), and 60 seconds (large) reduced to zero. This allows the velocity of H2 to be estimated. Calculate the turning acceleration based on the difference in turning rate between adjacent points P0, P1, and P2. If the turning acceleration is non-zero, the turning acceleration is calculated based on a time interval of 2 seconds reduced to zero. When the turning acceleration is zero, if the turning rate is non-zero, the turning rate is calculated based on a time interval of 15 seconds reduced to zero. This allows the direction and turning rate of H2 to be estimated.

[0112] H3 and later: Similar to H2, iterative calculations are performed. During iterations, velocity estimation errors and turning rate estimation errors are calculated. In subsequent position estimation, the acceleration decay rate is adjusted when the acceleration is not zero (referring to the H2 acceleration, which is fine-tuned to the value of 0 according to the ship type). The steering acceleration decay rate is adjusted when the steering acceleration is not zero (referring to the H2 steering acceleration, which decays to 0 over 2 seconds, and fine-tuning the 2-second value). The steering rate decay rate is adjusted when the steering acceleration is zero but the turning rate is not zero (referring to the H2 turning rate, which decays to 0 over 15 seconds, and fine-tuning the 15-second value). This ensures that the predicted ship trajectory is closer to the actual ship trajectory.

[0113] Ship track extrapolation of Class A AIS terminals, error calculation of position estimation, in P n The time calculation of the position point H n-1 The error is P n-1 Time to P n The result of the moment error accumulation is to calculate the average speed estimation error from the range error, and the average turning rate estimation error from the heading error. The calculation formula is as follows:

[0114] E v =E d / (t n -t n-1 )

[0115] E r=E c / (t n -t n-1 )

[0116] Where,

[0117] E d : range error;

[0118] E c : heading error;

[0119] t n : The measurement time of the latest position measurement point, that is, P n UTC time of the point;

[0120] t n-1 : The measurement time of the last position measurement point, that is, P n-1 The UTC time of the point.

[0121] See Figure 3 , the ship AIS trajectory extrapolation method based on state constraints in the embodiment of the present invention, the ship uses a Class B AIS terminal, P n (n=0, 1, 2, ..., ∞) is the ship position at time n reported by AIS, H n (n=1、2、3、...、∞) is the P at time n n and historical information (P n-1 、P n-2 、P n-3 , ...), and perform multi-hypothesis track extrapolation to calculate the position point. n The calculation is applicable to P n Afterwards n+1 Dead reckoning of position at any time during the previous time period. n The calculation method is as follows:

[0122] H1: Calculate the velocity and acceleration from the position and velocity differences between P0 and P1, and extrapolate according to linear motion. If the acceleration is not zero, the acceleration is calculated based on the ship type, taking 5 seconds (small), 15 seconds (small, medium and unknown types), 30 seconds (medium), and 60 seconds (large) respectively, minus to 0, to predict the position of H1.

[0123] H2: Velocity and acceleration are calculated from the position and velocity differences of P0, P1, and P2. If the acceleration is non-zero, the acceleration is calculated based on the vessel type, with a time interval of 5 seconds (small), 15 seconds (small, medium, and unknown), 30 seconds (medium), and 60 seconds (large) reduced to zero. This allows the position of H2 to be estimated. The turning rate and turning acceleration are calculated from the heading difference between two adjacent points of P0, P1, and P2. If the turning acceleration is non-zero, the turning acceleration is calculated based on a time interval of 2 seconds reduced to zero. If the turning rate is non-zero when the turning acceleration is zero, the turning rate is calculated based on a time interval of 15 seconds reduced to zero. This allows the direction and turning rate of H2 to be estimated.

[0124] H3 and later: Similar to H2, iterative calculations are performed. Similar to the basic ship extrapolation model for Class A AIS terminals, speed estimation errors and turning rate estimation errors are calculated during the iterations. These errors are then used in subsequent position estimation calculations, making the predicted ship trajectory closer to the actual ship motion trajectory.

[0125] The extrapolation process for Class B AIS terminals is applicable to ships that cannot obtain ship turning rate information from AIS reports. This includes ships equipped with Class B AIS terminals and ships equipped with Class A AIS terminals but without compass data (no valid heading data). This model does not use the ship's turning rate reported by the ship's AIS terminal, but only uses position, speed, and heading to estimate position.

[0126] Ship extrapolation of Class B AIS terminals, error calculation of position estimation, in P n+1 The time calculation of the position point H n The error is P n Time to P n+1 The result of the moment error accumulation is to calculate the average speed estimation error from the range error, and the average turning rate estimation error from the heading error. The calculation formula is as follows:

[0127] E v =E d / (t n+1 -t n )

[0128] E r =E c / (t n+1 -t n )

[0129] Where,

[0130] E d : range error;

[0131] E c : heading error;

[0132] t n: The measurement time of the latest position measurement point, that is, P n UTC time of the point;

[0133] t n+1 : The measurement time of the next position measurement point, that is, P n+1 The UTC time of the point.

[0134] Specifically, in step S3, the AIS trajectory of the ship is constrained according to the type and size of the ship, including setting the value of the constraint parameter K in the Av function, setting K = 5s for small ships, K = 15s for small, medium and unknown type ships, K = 30s for medium ships, and K = 60s for large ships.

[0135] Specifically, step S3 constrains the ship's AIS trajectory according to the navigation status, channel information, and channel collision avoidance rules, including the following steps:

[0136] S31: Constraining the vessel's navigation position using currently applicable channel information; the channel information includes digital channel information generated by electronic nautical charts or electronic river charts and empirical channel data generated by a large amount of AIS historical track data;

[0137] S32: constraining the ship's navigation speed, acceleration, turning rate and turning acceleration according to the current navigation status and the currently applicable collision avoidance rules;

[0138] S33: By adjusting the values ​​of the constraint parameters K, M, and N in the Ar function, the ship's position, speed, acceleration, turning rate, and turning acceleration are adjusted. When no adjustment is made, the values ​​of the constraint parameters M and N are 2s and 15s, respectively.

[0139] See Figure 4 In the state-constrained ship AIS trajectory extrapolation method of an embodiment of the present invention, the navigation state includes three states of two ships meeting each other: a head-on encounter state, a crossing encounter state, and an overtaking state. The ship's actions and maneuvering intentions are predicted according to the navigation state and collision avoidance rules. Based on the predicted ship maneuvering intentions, the speed, acceleration, turning rate, and turning acceleration in the track extrapolation model are constrained.

[0140] Please also see Figure 4 and Figure 5 A head-on encounter refers to the encounter between two vessels traveling along a waterway, including head-on or near-head-on encounters, encounters from port or starboard, and encounters on a curved channel, but does not include encounters between two crossing vessels. The main rules for avoidance action are: upstream vessels must give way to downstream vessels; upstream vessels must give way to downstream vessels; single vessels must give way to convoys; and, except in special circumstances, vessels must meet each other on the port side.

[0141] Each vessel is within 5° of the other's bow, and both the Closest Approach Distance (DCPA) and Minimum Approach Time (TCPA) are less than the specified values. Possible avoidance measures for the two vessels include: speed reduction; starboard rudder turn; speed reduction and starboard rudder turn.

[0142] When a ship has the responsibility to avoid, it will use the prior knowledge of "meeting on the port side" to perform a right-hand maneuver within a certain range. When extrapolating the track of such a ship during the avoidance measures, only the two factors of deceleration and right rudder should be considered, and then relatively strict constraints should be imposed on the speed and acceleration, turning rate and turning acceleration.

[0143] Please also see Figure 4 and Figure 6 Crossing state: The two ships are each located 5° to 112.5° outside the bow of the other ship to the left and right, that is, 5° < side angle < 112.5°, and DCPA and TCPA are less than the set values.

[0144] A vessel with another vessel on the starboard side of her should give way to the other vessel, that is, her should give way to the other vessel on the starboard side.

[0145] When crossing at a shallow angle, the give-way vessel should turn right and pass behind the stern of the straight-track vessel. When crossing at a large angle, if the two vessels are closely spaced, making right-hand clearance difficult and the area on the left is wide, a sharp left turn may be adopted. If the two vessels are closely spaced, a sharp right turn may be adopted to avoid the vessel, passing behind the straight-track vessel. If both right and left-hand clearances are difficult, the vessel may slow down or stop to allow the straight-track vessel to pass in front of the own vessel. Possible evasive measures when the own vessel is the give-way vessel include: slowing down; turning; and simultaneously slowing down and turning. Possible measures to maintain speed and direction when the own vessel is the straight-track vessel may be adopted.

[0146] When a ship is a give-way vessel at a small intersection, the ship will perform a right-hand maneuver within a certain range using the prior knowledge that "the give-way vessel turns right". When extrapolating the track of such a ship during the avoidance measure, only the deceleration and right rudder steering factors should be considered, and then relatively strict constraints should be imposed on the speed and acceleration, turning rate and turning acceleration.

[0147] When a vessel is giving way during a large-angle intersection, if it performs a turning maneuver, prior knowledge can be used to predict whether the subsequent maneuver will be a "small left turn" or a "large right turn." This allows for clear deceleration and turning factors, and thus imposes strict constraints on speed and acceleration, as well as the turning rate and acceleration. In the event of deceleration or stopping, turning is not performed until the intersection avoidance situation is no longer established. Therefore, while waiting for a turning maneuver, only deceleration is considered, resulting in stricter constraints on speed and acceleration.

[0148] Please also see Figure 4 and Figure 7 Overtaking state: When the angle of the leading vessel is greater than 22.5° behind the beam, the difference between the following vessel's course and the leading vessel's course is less than 60°, the two vessels are relatively close (visible to the human eye), and the following vessel is catching up with the leading vessel (the following vessel is relatively fast). The overtaken vessel maintains its speed and course during the overtaking process. The overtaking vessel may take the following actions during the overtaking process: acceleration; deceleration; and turning at the end of the overtaking process.

[0149] The overtaking vessel has the responsibility to avoid the overtaking vehicle during the maneuver. Speed ​​control will be implemented according to the different stages of the overtaking process, and turning operations can only be performed after the overtaking process is completed. Therefore, for the overtaking vessel during the overtaking process, the acceleration, turning acceleration, and turning rate are limited to 0. For the vessel in the process of overtaking, the turning rate and turning acceleration are limited to 0.

[0150] See Figure 8 In the state-constrained ship AIS trajectory extrapolation method according to an embodiment of the present invention, step S4 specifically includes:

[0151] S41: Determine the values ​​of constraint parameters K, M, and N according to the constraint range of the ship AIS trajectory extrapolation;

[0152] S42: Get the error parameter average speed error E of the previous reporting period v and the average turning rate error E r , calculate the acceleration error correction E av and steering acceleration error correction E ar ; Initialize the parameters of the Av function;

[0153] S43: Iteration S n-1 , γ n-1 、V n-1 、R n-1 、Av n-1 , solve for S n , γ n 、V n 、R n 、Av n 、Ar n ;

[0154] S44: Calculate the Av function, calculate Av at t n to t h The double integral of

[0155] S45: Calculate t n to t n +M interval Ar function, calculate Ar at t n to t n +M integral, calculate t n +M to t hAr function of the interval, calculate Ar at t n to t h The double integral of

[0156] S46: Calculate distance and azimuth change D h ,θ h , calculate t h The latitude and longitude at the moment.

[0157] Please also see Figure 9 In the state-constrained ship AIS trajectory extrapolation method according to an embodiment of the present invention, step S4 further includes calculating the error parameter of this reporting period, specifically as follows:

[0158] S51: Obtain the estimated position at the time of this report;

[0159] S52: Calculate the range error E based on the position, speed, heading and turning rate of the AIS information in this reporting period d and heading error E c ;

[0160] S53: Calculate and save the error parameters of this reporting period according to the reporting period, including the average speed error E v and the average turning rate error E r .

[0161] Specifically, in step S2, the current AIS information is obtained from the AIS message received by the ship's AIS terminal, and the historical AIS information is obtained from the ship's AIS historical track database.

[0162] For heading and rate of turn data in AIS information, if no rate of turn is reported, and the average error between the reported heading and the heading detected by track is less than 6 degrees, the reported heading data is trusted; otherwise, the heading data detected by track is trusted. If the average error between the reported rate of turn and the rate of turn calculated from the reported heading data is less than 5 degrees / second, the reported rate of turn is trusted; otherwise, the error between the rate of turn detected by track and the reported rate of turn is calculated. If the error between the reported rate of turn and the rate of turn detected by track is less than 10 degrees / second, the reported rate of turn is trusted; otherwise, the rate of turn calculated by track is used.

[0163] The heading data and navigation status data in AIS information can be used to predict the ship's movement pattern, especially in ports and anchorages. The changes in heading, combined with changes in course and position, can be used to predict the change between anchoring or mooring and navigation status. If the navigation status data reported by the ship is reliable, the navigation status can be used to predict the ship's movement pattern, especially in ports and anchorages. The changes between navigation status and mooring or anchoring status can be used to predict the ship's subsequent movement.

[0164] Vessel type is categorized based on the message number used for reporting position and static data, as well as the content of the static data. The type and size of a vessel can be obtained from the AIS vessel database and static messages in the AIS historical database, ensuring the algorithm accurately and effectively selects appropriate vessel type parameters. If the reported size information is available, ships are prioritized by size: vessels less than 25 meters in length are classified as small, those greater than 25 meters but less than 70 meters are classified as small and medium-sized, those greater than 70 meters but less than 115 meters are classified as medium-sized, and those greater than 115 meters are classified as large.

[0165] If there is no size information but there is ship type information, the second best option is to classify by ship type. Please refer to Table 1 below: Ship type classification table.

[0166] Table 1 Classification of ship types

[0167] type Classification for application in inland water areas Classification for application in coastal areas passenger ship Small ships Small and medium-sized ships cargo ship Small and medium-sized ships Small and medium-sized ships tanker Small and medium-sized ships medium-sized ships Flying Wing Ship Small ships Small and medium-sized ships fishing boat Small ships Small and medium-sized ships Towing boat Small and medium-sized ships Small and medium-sized ships Long towing vessel Large ships Large ships Dredger or underwater operation vessel Small and medium-sized ships medium-sized ships Diving operation boat Small and medium-sized ships Small and medium-sized ships Military work boat Small and medium-sized ships Small and medium-sized ships sailboat Small ships Small ships leisure yachts Small ships Small ships high speed boat Small ships Small ships pilot boat Small ships Small ships Search and rescue boat Small ships Small ships tugboat Small ships Small ships Port supply vessel Small and medium-sized ships Small and medium-sized ships Anti-pollution ships Small and medium-sized ships Small and medium-sized ships law enforcement ship Small ships Small ships Medical transport ship Small and medium-sized ships Small and medium-sized ships Other types of ships Small and medium-sized ships Small and medium-sized ships type Classification for application in inland water areas Classification for application in coastal areas passenger ship Small ships Small and medium-sized ships

[0168] In summary, the state-constrained ship AIS trajectory extrapolation method of the embodiment of the present invention is based on the rule that the ship's motion acceleration automatically decays over time, utilizes the ship's static information, ship type, size, etc., route history information, ship encounter maneuvering rules, verifies the ship's historical motion parameters, estimates the ship's inertia and maneuverability, and estimates the ship's motion trajectory, thereby more accurately fitting the ship's motion trajectory.

[0169] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the definition of the claims.

Claims

1. A ship AIS trajectory extrapolation method based on state constraints, characterized by: The steps include: S1: Establish a ship AIS trajectory extrapolation model; S2: Obtain basic information of the ship and the ship's AIS information; the basic information of the ship includes the ship's type, size, current navigation status, currently applicable channel information, and currently applicable collision avoidance regulations; the AIS information of the ship includes the ship's current AIS information and historical AIS information, and the AIS information includes the ship's position, speed, heading, and turning rate information; S3: Constrain the ship's AIS trajectory based on the ship's basic information and set the constraint range for the ship's AIS trajectory extrapolation; S4: Estimate the ship's position, speed, acceleration, turning rate, and turning acceleration at future times using the ship's AIS trajectory extrapolation model based on the ship's AIS information and the constraints of the ship's AIS trajectory extrapolation. In step S1, a ship AIS trajectory extrapolation model is established based on the automatic decay of the ship's motion acceleration over time. The calculation formulas for the various parameters in the ship AIS trajectory extrapolation model are as follows: D h = V n (t h - t n )+∫∫Av t n ≤t≤t h θ h = R n (t h - t n )+∫∫Ar t n ≤t≤t h Where: V n = S n / (t n - t n-1 ) R n = γ n / (t n - t n-1 ) Off = Off n (1 - (1 / K)*t)+ E av t n +0.0≤t≤t n +K Off = 0.0 hr n +K<t≤t h Ar is a piecewise function, the first part is the function of the first M seconds, and the second part is the function after M seconds; Ar = Ar n (1 - 1 / M*t) t n +0.0≤t≤t n +M Ar = R k / N + E ar t n +M<t≤t n +M+N Ar = 0.0 t n +M+N<t≤t h In the piecewise function of Ar, Ar n =(R n - R n-1 ) / (t n - t n-1 ) t n +0.0≤t≤t n +M R k = R n +∫Ar t n +0.0≤t≤t n +M in, Av: acceleration function; Ar: steering acceleration function; t n : The measurement time of the latest position measurement point, that is, P n UTC time of the point; t n-1 : The measurement time of the last position measurement point, that is, P n-1 UTC time of the point; t h : The predicted time of the predicted location point; D h :Predicted location point and P n The estimated distance change of the location point; θ h :Predicted location point and P n Estimated heading change of the position point; V n : The speed of the latest position measurement point, that is, P n The speed of the point; V n-1 : The speed of the last position measurement point, that is, P n-1 The speed of the point; R n : The turning speed (turn rate) of the latest position measurement point, that is, P n The turning speed of the point; R n-1 : The turning speed (turn rate) of the last position measurement point, that is, P n-1 The turning speed of the point; S n : Track point P n To track point P n-1 The distance difference; γ n : Track point P n To track point P n-1 The distance and heading angle difference; Av n : The acceleration of the latest position measurement point, that is, P n The acceleration of the point; Av n-1 : The acceleration of the last position measurement point, that is, P n-1 The acceleration of the point; Ar n : The steering acceleration of the latest position measurement point, that is, P n The turning acceleration of the point; Ar n-1 : The steering acceleration of the last position measurement point, that is, P n-1 The turning acceleration of the point; E av : acceleration error correction; E ar : Steering acceleration error correction; K: The time it takes for the ship's acceleration to decrease to 0; M: The time it takes for the ship's steering acceleration to decrease to 0; N: The time it takes for the ship's turning speed to decrease to 0.

2. The ship AIS trajectory extrapolation method based on state constraints according to claim 1 is characterized in that: The acceleration error correction amount E av and steering acceleration error correction E ar The calculation formula is as follows: It is av =E v / Your E ar =E r / Tr Where, E v : average velocity error; Ta: the time it takes for the acceleration to decay to 0; E r : average turning rate error; Tr: The time it takes for the steering acceleration to decay to 0.

3. The ship AIS trajectory extrapolation method based on state constraints according to claim 2 is characterized in that: The average speed error E v and the average turning rate error E r The calculation formula is as follows: E v = E d / (t n -t n-1 ) E r = E c / (t n -t n-1 ) Where, E d : range error; E c : heading error; t n : The measurement time of the current position measurement point, that is, P n UTC time of the point; t n-1 : The measurement time of the previous position measurement point, that is, P n-1 The UTC time of the point.

4. The ship AIS trajectory extrapolation method based on state constraints according to claim 1 is characterized in that: In step S3, the AIS trajectory of the ship is constrained according to the type and size of the ship, including setting the value of the constraint parameter K in the Av function, setting K=5s for small ships, K=15s for small, medium and unknown type ships, K=30s for medium ships, and K=60s for large ships.

5. The ship AIS trajectory extrapolation method based on state constraints according to claim 1 is characterized in that: Step S3 constrains the ship's AIS trajectory according to the current navigation status, the currently applicable channel information, and the currently applicable collision avoidance rules, including the following steps: S31: Constraining the vessel's navigation position using currently applicable channel information; the channel information includes digital channel information generated by electronic nautical charts or electronic river charts and empirical channel data generated by a large amount of AIS historical track data; S32: constraining the ship's navigation speed, acceleration, turning rate and turning acceleration according to the current navigation status and the currently applicable collision avoidance rules; S33: By adjusting the values ​​of the constraint parameters K, M and N in the Ar function, the position, speed, acceleration, turning rate and turning acceleration of the ship's navigation are adjusted.

6. The ship AIS trajectory extrapolation method based on state constraints according to claim 5 is characterized in that: The navigation state includes three states of two ships meeting each other, namely, a head-on encounter state, a crossing encounter state, and an overtaking state. Step S32 includes: predicting the actions and maneuvering intentions of the ships according to the navigation state according to the collision avoidance rules, and constraining the speed, acceleration, turning rate, and steering acceleration in the track extrapolation model according to the predicted maneuvering intentions of the ships.

7. The ship AIS trajectory extrapolation method based on state constraints according to claim 4 is characterized in that: The step S4 comprises: S41: Determine the values ​​of constraint parameters K, M, and N according to the constraint range of the ship AIS trajectory extrapolation; S42: Get the error parameter average speed error E of the previous reporting period v and the average turning rate error E r , calculate the acceleration error correction E av and steering acceleration error correction E ar ; Initialize the parameters of the Av function; S43: Iterate S n-1 , γ n-1 , V n-1 , R n-1 , Av n-1 , solve for S n , γ n , V n , R n , Av n , Ar n ; S44: Calculate the Av function, calculate Av at t n to t h The double integral of S45: Calculate t n to t n +M interval Ar function, calculate Ar at t n to t n +M integral, calculate t n +M to t h Ar function of the interval, calculate Ar at t n to t h The double integral of S46: Calculate distance and azimuth change D h ,θ h , calculate t h The latitude and longitude at the moment.

8. The ship AIS trajectory extrapolation method based on state constraints according to claim 7 is characterized in that: Step S4 also includes calculating the error parameter for this reporting period, the steps are as follows: S51: Obtain the estimated position at the time of this report; S52: Calculate the range error E based on the position, speed, heading and turning rate of the AIS information in this reporting period d and heading error E c ; S53: Calculate and save the error parameters of this reporting period according to the reporting period, including the average speed error E v and the average turning rate error E r .

9. The ship AIS trajectory extrapolation method based on state constraints according to claim 1, characterized in that: In step S2, current AIS information is obtained from AIS messages received by the ship's AIS terminal, and historical AIS information is obtained from a ship's AIS historical track database.

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