CN111724629B

CN111724629B - AIS ship track extrapolation method for video monitoring system

Info

Publication number: CN111724629B
Application number: CN202010582791.9A
Authority: CN
Inventors: 倪侃俊; 徐燕
Original assignee: Shanghai Advanced Avionics Co ltd
Current assignee: Shanghai Aiwei Information Technology Co ltd
Priority date: 2020-06-23
Filing date: 2020-06-23
Publication date: 2021-10-29
Anticipated expiration: 2040-06-23
Also published as: CN111724629A

Abstract

The invention discloses an AIS ship track extrapolation method for a video monitoring system, which comprises the following steps: s1: acquiring AIS information of a current moment and at least two moments of a ship, and acquiring track point positions and corresponding moments of the current moment and the at least two moments; s2: obtaining a radial distance value and an angle value of the track point position relative to the reference point through the known reference point position and the known track point position; s3: calculating a radial velocity value and an angular velocity value between two continuous moments; s4: calculating a radial acceleration value and an angular acceleration value at two moments; s5: and calculating to obtain the position of the extrapolated track point according to a track extrapolation formula by the speed value and the acceleration value. The invention combines the factors of the position, time, speed, steering and the like of the ship, and simultaneously integrates the relationship between the monitoring camera and the ship to extrapolate the track, thereby improving the accuracy of AIS ship track extrapolation.

Description

AIS ship track extrapolation method for video monitoring system

Technical Field

The invention relates to a ship track extrapolation method, in particular to an AIS ship track extrapolation method for a video monitoring system.

Background

An Automatic Identification System (AIS) for ships is composed of shore-based (base station) facilities and shipborne equipment, and is a novel digital navigation aid system and equipment integrating network technology, modern communication technology, computer technology and electronic information display technology. The AIS system is matched with a Global Positioning System (GPS) to broadcast the ship position, ship speed, changed course rate and course and other ship dynamic data combined with ship name, call sign, draft, dangerous goods and other ship static data from Very High Frequency (VHF) to ships and shore stations in nearby water areas, so that the nearby ships and shore stations can timely master the dynamic and static information of all ships on nearby sea surfaces, and can immediately communicate and coordinate with each other, take necessary avoidance actions and effectively guarantee the navigation safety of the ships.

The ship dynamic video monitoring system is often integrated in a ship traffic management system and is used for dynamically monitoring ship navigation in a port area so as to make up for the defects that a radar has a blind area, is easy to be interfered by electrons, has no real image and the like, and the importance of the video system in the whole ship traffic management system is gradually enhanced. The video monitoring has the advantage of flexible installation, particularly along with the development of an intelligent ball technology, a video camera capable of rotating freely without dead angles of 360 degrees horizontally and 90 degrees vertically is popularized, IP network video transmission also enables low-cost remote deployment, the application of technologies such as active infrared shooting, polarization filtering shooting and the like ensures the annual available days of video monitoring, ship coordinate position data received by AIS is converted into a preset position of an intelligent ball holder to drive the video camera to turn to a monitoring object, automatic video tracking of a ship can be realized, and the video monitoring becomes an important supplement of port safety management.

Due to the reporting interval mechanism of the AIS equipment, the ship coordinate position reporting interval time of the A-type ship-mounted equipment with the moving speed of 14 sections and the B-type ship-mounted equipment with the moving speed of 23 sections exceeds 10 seconds, and the longest interval time even reaches 3 minutes. The problem that ship tracking is lost frequently occurs in automatic video tracking of a ship by a ship dynamic video monitoring system, namely, the ship sails to a far place, and the video camera sends the preset position of the AIS ship coordinate position on the tracked ship for one time.

Therefore, it is necessary to provide an AIS ship track extrapolation algorithm for a ship dynamic video monitoring system, which extrapolates a possible track point at the next moment through a ship's sailing track, and improves the automatic video tracking capability of the ship.

Disclosure of Invention

The invention aims to solve the technical problem of providing an AIS ship track extrapolation method for a video monitoring system, which combines the factors of the position, time, speed, steering and the like of a ship and integrates the relationship between a monitoring camera and the ship to extrapolate the ship track, so that the accuracy is high.

The invention adopts the technical scheme that an AIS ship track extrapolation method for a video monitoring system is provided to solve the technical problems, and comprises the following steps: s1: acquiring AIS information of a ship at the current moment and at least two moments, and finding track point positions and corresponding moments of the current moment and the at least two moments; s2: obtaining a radial distance value and an angle value of the track point position relative to the reference point through the known reference point position and the known track point position; s3: calculating the difference between the radial distance values and the angle values of the track point positions at two continuous moments to obtain a radial speed value and an angular speed value between the two continuous moments; s4: calculating the difference between the radial velocity values and the angular velocity values between two continuous moments and the difference between the two continuous moments to obtain the radial acceleration value and the angular acceleration value at the two moments; s5: and calculating to obtain the position of the extrapolated track point according to a track extrapolation formula by the speed value and the acceleration value.

Further, in the step S1, the track point position is a longitude and latitude of the track point, and the corresponding time is a timestamp corresponding to the track point; setting the obtained track positions as P (n-2), P (n-1) and P (n), and setting the extrapolated track positions as P (n + x 1) and P (n + x 2); the corresponding acquired time is T (n-2), T (n-1) and T (n), the extrapolated time is T (n + x 1) and T (n + x 2), and T (n + x 1) and T (n + x 2) are obtained by superposing T (n) for a fixed time T.

Further, the reference point known in step S2 is the position of the surveillance camera, and the angle value is an arc value of an included angle from the north of the position of the surveillance camera to the track point; the radial distance values of the track point positions obtained through calculation are r (n-2), r (n-1) and r (n), and the radial distance values of the extrapolated track point positions are r (n + x 1) and r (n + x 2); the angle values of the track point positions are theta (n-2), theta (n-1) and theta (n), and the angle values of the extrapolated track point positions are theta (n + x 1) and theta (n + x 2).

Further, in step S3, the radial speed values between the track positions are Vr (n-1) and Vr (n), the radial speed value between the extrapolated track position and Vr (n + x 1), Vr (n + x 2), and Vr (n) is calculated as: vr (n) = (r (n) -r (n-1))/(t (n) -t (n-1));

the angular velocity values between the track point positions are V theta (n-1) and V theta (n), the angular velocity values between the extrapolated track point positions are V theta (n + x 1) and V theta (n + x 2), and the calculation formula of V theta (n) is as follows: v θ (n) = (θ (n) - θ (n-1))/(t (n) -t (n-1)).

Further, in the step S4, the radial acceleration values are ar (n), ar (n + x 1), ar (n + x 2), and ar (n) is calculated as the following formula: ar (n) = (Vr (n) -Vr (n-1))/(t (n) -t (n-1)); angular acceleration values are a theta (n), a theta (n + x 1), a theta (n + x 2), and a theta (n) is calculated by the formula: a θ (n) = (V θ (n) -V θ (n-1))/(t (n) -t (n-1)).

Further, the step S5 specifically includes, S51: judging whether the angular acceleration value a theta (n) and the radial acceleration value ar (n) are smaller than | A |, wherein A is a set acceleration threshold value, and | A | is smaller than or equal to 0.1; s52: if the angular acceleration value a theta (n) and the radial acceleration value ar (n) are smaller than | A |, the motion is considered to be uniform motion, V theta (n + x 1) = V theta (n), Vr (n + x 1) = Vr (n); if the angular acceleration value a theta (n) and the radial acceleration value ar (n) are greater than or equal to | A |, the acceleration is considered as acceleration motion, and V theta (n + x 1) = V theta (n) + a theta (n) × T and Vr (n + x 1) = Vr (n) + ar (n) × T are obtained through an acceleration motion formula; t is an extrapolation interval time which is an adjustable fixed value, and T is 0.5s or 1 s; s53: obtaining a radial distance value r (n + x 1) = r (n) + Vr (n + x 1) × T and an angle value θ (n + x 1) = θ (n) + V θ (n + x 1) × T of the extrapolated track point relative to the reference point through V θ (n + x 1) and Vr (n + x 1); s54: and calculating the longitude and latitude P' (n + x 1) of the extrapolated locus point according to the position of the reference point, namely the longitude and latitude of the reference point, and the radial distance value and the angle value of the extrapolated locus point relative to the reference point.

Further, correcting the longitude and latitude of the extrapolated locus points obtained through calculation according to the turning rate of the ship during moving to obtain the corrected longitude and latitude P (n + x 1) of the extrapolated locus points; setting the turning rate of the ship when moving as C (n), judging whether the turning rate C (n) is less than | P |, wherein P is a set turning rate threshold value, | P | < 5, if the turning rate C (n) is less than | P |, the ship is considered to be in linear motion, and the longitude and latitude P (n + x 1) = P' (n + x 1) of the corrected extrapolated track point; if the steering rate C (n) is greater than or equal to | P |, the curve motion is considered, the longitude and latitude P (n + x 1) of the track point subjected to the correction extrapolation is obtained through P (n), P' (n + x 1) and C (n), and the track extrapolation formula is as follows: p (n + x 1) = f (P' (n + x 1), c (n));

further, the steering rate C (n) is the steering frequency of the ship and is acquired through an AIS system.

Compared with the prior art, the invention has the following beneficial effects: the AIS ship track extrapolation method for the video monitoring system, provided by the invention, has the advantages that 1) the AIS ship track extrapolation accuracy is improved; 2) the automatic video tracking efficiency of the ship in the dynamic video monitoring of the ship is improved; 3) the navigation method has the advantages that the navigation track of the ship at the next moment can be extrapolated, and the important effect is played for guaranteeing the navigation safety of the ship; 4) the supervision ability of the maritime supervision department on the ship is improved.

Drawings

FIG. 1 is a flow chart of an AIS ship track extrapolation method for a video monitoring system according to an embodiment of the present invention;

fig. 2 is a schematic diagram of an AIS ship track extrapolation method for a video monitoring system according to an embodiment of the present invention.

Detailed Description

The invention is further described below with reference to the figures and examples.

FIG. 1 is a flow chart of an AIS ship track extrapolation method for a video monitoring system according to an embodiment of the present invention; fig. 2 is a schematic diagram of an AIS ship track extrapolation method for a video monitoring system according to an embodiment of the present invention.

Referring to fig. 1 and fig. 2, the AIS ship track extrapolation method for the video monitoring system according to the embodiment of the present invention includes the following specific steps:

step 1: the AIS information of the ship at the current moment and the AIS information of the ship at the last two moments are found firstly, and the track point positions (longitude and latitude) and the moments (time stamps) of the current moment and the last two moments are found, the algorithm at least needs 3 continuous moments to extrapolate the track, and the extrapolation is more accurate when the number is larger.

1) Track point position (latitude and longitude): p (n-2), P (n-1), P (n + x 1), P (n + x 2), wherein P (n + x 1) and P (n + x 2) are extrapolated positions;

2) time of day (timestamp): t (n-2), T (n-1), T (n + x 1) and T (n + x 2), wherein T (n + x 1) and T (n + x 2) are extrapolation moments and are obtained by superposing T (n) for a fixed time T;

step 2: and obtaining corresponding radial distance values and angle values through the known reference point positions and track point positions (longitude and latitude) of the ship.

1) Radial distance value: r (n-2), r (n-1), r (n + x 1), r (n + x 2) are the distances from the surveillance camera position to the track point; wherein r (n + x 1) and r (n + x 2) are extrapolation distances;

2) angle value: theta (n-2), theta (n-1), theta (n + x 1) and theta (n + x 2) are included angles (unit: radian) from the northward direction of the position of the monitoring camera to a track point, namely the initial angle (0); wherein θ (n + x 1) and θ (n + x 2) are extrapolation angles;

and step 3: and calculating the difference between the radial distance value and the angular value at two continuous moments (such as the current moment and the last moment) and the difference between the moments at two continuous moments (such as the current moment and the last moment) respectively to obtain corresponding angular velocity value and radial velocity value.

1) Angular velocity values: v theta (n-1), V theta (n + x 1) and V theta (n + x 2) are the difference between the current angle value and the previous angle value/the difference between the current time and the previous time;

the formula: v θ (n) =Δθ n/. DELTA t n = (θ (n) - θ (n-1))/(t (n) -t (n-1));

2) radial velocity value: vr (n-1), Vr (n + x 1) and Vr (n + x 2) are the difference between the current radial distance value and the previous radial distance value/the difference between the current time and the previous time;

the formula: vr (n) = Δ rn/. DELTA. t n = (r (n) -r (n-1))/(t (n) -t (n-1)).

And 4, step 4: and calculating the difference between the radial velocity values and the angular velocity values at two continuous moments (such as the current moment and the last moment) and the difference between the moments at two continuous moments (such as the current moment and the last moment) respectively to obtain corresponding angular acceleration values and radial acceleration values.

1) Angular acceleration value: a theta (n), a theta (n + x 1) and a theta (n + x 2) are the difference between the current angular velocity value and the previous angular velocity value/the difference between the current time and the previous time;

the formula: a θ (n) = Δ V θ n/. DELTA t n = (V θ (n) -V θ (n-1))/. DELTA t n;

2) radial acceleration value: ar (n), ar (n + x 1), ar (n + x 2) are the difference between the current radial velocity value and the previous radial velocity value/the difference between the current time and the previous time;

the formula: ar (n) = Δ Vrn/. DELTA t n = (Vr (n) -Vr (n-1))/. DELTA t n.

And 5: and finally, calculating the required extrapolated position through the speed and the acceleration:

judging whether the angular acceleration value a theta (n) and the radial acceleration value ar (n) are smaller than | A |, wherein A is a set acceleration threshold value, and | A | is recommended to be smaller than or equal to 0.1;

if the angular acceleration value a theta (n) and the radial acceleration value ar (n) are smaller than | A |, the motion is considered to be uniform motion, V theta (n + x 1) = V theta (n), Vr (n + x 1) = Vr (n);

if the angular acceleration value a theta (n) and the radial acceleration value ar (n) are greater than or equal to | A |, the acceleration is considered as acceleration motion, and V theta (n + x 1) = V theta (n) + a theta (n) × T and Vr (n + x 1) = Vr (n) + ar (n) × T are obtained through an acceleration motion formula; t is an extrapolation interval time which is an adjustable fixed value, and T is 0.5s or 1 s;

obtaining a radial distance value r (n + x 1) = r (n) + Vr (n + x 1) × T and an angle value θ (n + x 1) = θ (n) + V θ (n + x 1) × T of the extrapolated track point relative to the reference point through V θ (n + x 1) and Vr (n + x 1);

and calculating the longitude and latitude P' (n + x 1) of the extrapolated locus point according to the position of the reference point, namely the longitude and latitude of the reference point, and the radial distance value and the angle value of the extrapolated locus point relative to the reference point.

The turning rate C (n) of the ship is also considered during calculation, and the longitude and latitude of the extrapolated track point obtained through calculation are corrected through the turning rate during the movement of the ship, so that the corrected longitude and latitude P (n + x 1) of the extrapolated track point is obtained;

judging whether the steering rate C (n) is less than | P |, wherein P is a set steering rate threshold value, and suggesting | P | < 5;

if the steering rate C (n) is less than | P |, the motion is considered to be linear motion, and the corrected longitude and latitude P (n + x 1) = P' (n + x 1) of the extrapolated track point;

if the steering rate C (n) is greater than or equal to | P |, the curve motion is considered, the longitude and latitude P (n + x 1) of the track point subjected to the correction extrapolation is obtained through P (n), P' (n + x 1) and C (n), and the track extrapolation formula is as follows: p (n + x 1) = f (P' (n + x 1), c (n));

and the steering rate C (n) is the steering frequency of the ship and is acquired by an AIS system.

In summary, the AIS ship track extrapolation method for the video monitoring system according to the embodiment of the present invention combines the position, time, speed, and direction of the ship, and integrates the relationship between the monitoring camera and the ship, and obtains the corresponding radial distance and angle values through the AIS information at the continuous time; then, calculating the difference between the radial distance values and the angle values and the difference between the moments to obtain corresponding angular speed values and radial speed values; and then calculating an acceleration value to describe the speed change physical quantity of the ship on the radial distance and the angle value, and finally obtaining a required extrapolation position through a track extrapolation formula to improve the AIS ship track extrapolation accuracy.

Although the present invention has been described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. An AIS ship track extrapolation method for a video monitoring system is characterized by comprising the following steps:

s1: acquiring AIS information of a ship at the current moment and at least two moments, and finding track point positions and corresponding moments of the current moment and the at least two moments;

s2: obtaining a radial distance value and an angle value of the track point position relative to the reference point through the known reference point position and the known track point position;

s3: calculating the difference between the radial distance values and the angle values of the track point positions at two continuous moments to obtain a radial speed value and an angular speed value between the two continuous moments;

s4: calculating the difference between the radial velocity values and the angular velocity values between two continuous moments and the difference between the two continuous moments to obtain the radial acceleration value and the angular acceleration value at the two moments;

s5: calculating to obtain an extrapolated track point position according to a track extrapolation formula through the speed value and the acceleration value;

in the step S1, the track point position is the longitude and latitude of the track point, and the corresponding time is the timestamp corresponding to the track point; setting the obtained track positions as P (n-2), P (n-1) and P (n), and setting the extrapolated track positions as P (n + x 1) and P (n + x 2); the obtained corresponding time is T (n-2), T (n-1) and T (n), the extrapolated time is T (n + x 1) and T (n + x 2), and T (n + x 1) and T (n + x 2) are obtained by overlapping T (n) with a fixed time T;

the known reference point position in the step S2 is the position of the surveillance camera, and the angle value is an arc value of an included angle from the north direction of the position of the surveillance camera to the track point; the radial distance values of the track point positions obtained through calculation are r (n-2), r (n-1) and r (n), and the radial distance values of the extrapolated track point positions are r (n + x 1) and r (n + x 2); the angle values of the track point positions are theta (n-2), theta (n-1) and theta (n), and the angle values of the extrapolated track point positions are theta (n + x 1) and theta (n + x 2);

in step S3, the radial speed values between the track positions are Vr (n-1) and Vr (n), the radial speed value between the extrapolated track position and Vr (n + x 1) and Vr (n + x 2), and the Vr (n) is calculated by the following formula: vr (n) = (r (n) -r (n-1))/(t (n) -t (n-1));

the angular velocity values between the track point positions are V theta (n-1) and V theta (n), the angular velocity values between the extrapolated track point positions are V theta (n + x 1) and V theta (n + x 2), and the calculation formula of V theta (n) is as follows: v θ (n) = (θ (n) - θ (n-1))/(t (n) -t (n-1));

in the step S4

Radial acceleration values ar (n), ar (n + x 1), ar (n + x 2),

ar (n) is calculated as: ar (n) = (Vr (n) -Vr (n-1))/(t (n) -t (n-1));

the angular acceleration values are a theta (n), a theta (n + x 1) and a theta (n + x 2),

a θ (n) calculation formula: a θ (n) = (V θ (n) -V θ (n-1))/(t (n) -t (n-1));

the step S5 specifically includes:

s51: judging whether the angular acceleration value a theta (n) and the radial acceleration value ar (n) are smaller than | A |, wherein A is a set acceleration threshold value, and | A | is smaller than or equal to 0.1;

s52: if the angular acceleration value a theta (n) and the radial acceleration value ar (n) are smaller than | A |, the motion is considered to be uniform motion, V theta (n + x 1) = V theta (n), Vr (n + x 1) = Vr (n);

s53: obtaining a radial distance value r (n + x 1) = r (n) + Vr (n + x 1) × T and an angle value θ (n + x 1) = θ (n) + V θ (n + x 1) × T of the extrapolated track point relative to the reference point through V θ (n + x 1) and Vr (n + x 1);

s54: calculating to obtain the longitude and latitude P' (n + x 1) of the extrapolated locus point according to the position of the reference point, namely the longitude and latitude of the reference point, and the radial distance value and the angle value of the extrapolated locus point relative to the reference point;

correcting the longitude and latitude of the extrapolated locus points obtained through calculation according to the turning rate of the ship during moving to obtain the corrected longitude and latitude P (n + x 1) of the extrapolated locus points; setting the turning rate of the ship when moving as C (n), judging whether the turning rate C (n) is less than | P |, wherein P is a set turning rate threshold value, | P | < 5, if the turning rate C (n) is less than | P |, the ship is considered to be in linear motion, and the longitude and latitude P (n + x 1) = P' (n + x 1) of the corrected extrapolated track point; if the steering rate C (n) is greater than or equal to | P |, the curve motion is considered, the longitude and latitude P (n + x 1) of the track point subjected to the correction extrapolation is obtained through P (n), P' (n + x 1) and C (n), and the track extrapolation formula is as follows: p (n + x 1) = f (P' (n + x 1), c (n)).

2. The AIS ship track extrapolation method for video monitoring system according to claim 1 wherein the steering rate C (n) is ship steering frequency, acquired by AIS system.