Ship monitoring equipment

Abstract

[Problem] To provide a vessel monitoring device that allows a user to intuitively and easily recognize information on the possibility of a collision. [Solution] A vessel maneuvering support device 1 comprises a risk map generation unit 51 and a display data generation unit 61. When the position, which is on a planned course estimated for a second vessel and determined to evaluate the risk of a first vessel colliding with the second vessel, is called a risk evaluation position assuming veering of the first vessel among a plurality of vessels, the risk map generation unit 51 estimates the possibility of collision between the first vessel and the second vessel at a position other than the risk evaluation position, and generates a risk map showing the distribution of the estimated possibility of a collision. The display data generation unit 61 generates display data for displaying the risk map.

Description

[Technical field]

[0001] The present invention relates to a vessel monitoring device. [Background technology]

[0002] Conventionally, there has been known a ship monitoring device that can calculate a zone where a collision between ships will occur in the future by using ship navigation information. Non-Patent Document 1 discloses a calculation method of the zone by this type of ship monitoring device.

[0003] Non-Patent Document 1 discloses a method for calculating OZT (Obstacle Zone by Target). In the calculation of OZT described in Non-Patent Document 1, evaluation points are set at appropriate intervals on the planned route of the predicted other ship, and the collision risk at each evaluation point is calculated. If an evaluation point has a collision risk that exceeds the set threshold, a circle of an appropriate size is displayed with the evaluation point as its center. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Junji Fukuto and Junma Imazu: Study on collision warning using OZT (Obstruction Zone of Target), Journal of the Japan Institute of Navigation, vol. 128, pp. 49-54, March 2013. Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method of the above-mentioned Patent Document 1 shows the OZT with a circle of an appropriate size for each evaluation point, and depending on the situation, the circles can become crowded and difficult to see. Also, with the conventional OZT, even when a circle is displayed, the ship operator has to use his imagination to judge whether the collision risk around the circle is high or not, and there has been a demand for a ship monitoring device that can provide users with easy-to-understand information from a wider perspective.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a ship monitoring device that allows a user to intuitively and easily obtain information regarding the possibility of collision.

[0007] The problem to be solved by the present invention has been described above. Next, the means for solving this problem and the effects thereof will be described.

[0008] According to an aspect of the present invention, there is provided a ship monitoring device having the following configuration. That is, the ship monitoring device includes a risk map generation unit and a display data generation unit. When a position on a planned course estimated for a second ship among a plurality of ships is called a risk assessment position, which is determined to assess the risk of a first ship colliding with another second ship assuming that the first ship changes course, the risk map generation unit estimates the possibility of collision between the first ship and the second ship at positions other than the risk assessment position, and generates a risk map showing the distribution of the estimated possibility of collision. The display data generation unit generates display data for displaying the risk map.

[0009] This allows users to intuitively understand the possibility of a collision between a first vessel and a second vessel over a wider area than with conventional OZT, by using a risk map that estimates the possibility of a collision with a second vessel when the first vessel changes course, even at locations different from the risk assessment location.

[0010] The ship monitoring device is preferably configured as follows. That is, the ship monitoring device includes an information acquisition unit and a collision risk calculation unit. The information acquisition unit acquires navigation information of a plurality of ships. The collision risk calculation unit calculates a collision risk value indicating the risk of collision between the first ship and the second ship for the risk assessment position using the navigation information. The risk map generation unit estimates collision risk values ​​at positions other than the risk assessment position, and generates a risk map indicating the distribution of the estimated collision risk values.

[0011] This allows the user to understand more specifically the possibility of a collision between the first vessel and the second vessel by using a risk map that shows estimated collision risk values ​​at positions other than the risk assessment position.

[0012] In the above-mentioned ship monitoring device, it is preferable that the risk map generation unit estimates collision risk values ​​at positions other than the risk assessment position by utilizing a function that can interpolate surrounding collision risk values ​​based on the risk assessment position, and generates a risk map showing the distribution of the estimated collision risk values.

[0013] This allows the user to intuitively understand the possibility of a collision in the vicinity of the risk assessment position by looking at a risk map in which collision risk values ​​in the vicinity of the risk assessment position are interpolated.

[0014] In the ship monitoring device, it is preferable that the risk map generation unit generates the risk map by adding up Kernel functions centered on each of the risk assessment positions.

[0015] In this way, by using a smoothly changing kernel function, it is possible to estimate a collision risk value at a position that is not a risk assessment position so that the collision risk value changes smoothly in response to changes in position.

[0016] In the ship monitoring device, the kernel function is preferably a Gaussian function.

[0017] This makes it possible to appropriately estimate the collision risk value at a position that is not a risk assessment position.

[0018] The ship monitoring device preferably further comprises a ship designation unit capable of selecting and designating the first ship from the plurality of ships.

[0019] This makes it possible to analyze the risk of collision from various perspectives by switching the selection of the first vessel while displaying the risk map.

[0020] The ship monitoring device is preferably configured as follows: That is, the ship monitoring device is provided on a ship, and the ship designation unit is capable of designating another ship around the ship as the first ship.

[0021] This makes it possible to grasp the risk of collision from the perspective of other ships using the risk map, making it easier to predict the evasive actions of other ships.

[0022] The ship monitoring device is preferably configured as follows: That is, the ship monitoring device is provided on a ship, and the risk map generation unit is capable of generating the risk map in a case where the first ship and the second ship are both other ships around the ship.

[0023] This allows ships to maneuver while keeping track of the risk of collision with other ships using the risk map.

[0024] The ship monitoring device is preferably provided at a land facility.

[0025] This makes it possible to display the risk of collision between ships in an easily understandable manner to a user, for example, in an application where ships passing through a harbor are monitored.

[0026] In the ship monitoring device, it is preferable that the risk map generation unit generates the risk map by synthesizing a distribution of collision probability when each of a plurality of ships is defined as the first ship.

[0027] This makes it possible to clearly display areas with a high / low overall risk of collision in situations involving multiple ships. [Brief description of the drawings]

[0028] [Figure 1]1 is a block diagram showing an electrical configuration of a ship steering assistance device according to an embodiment of the present invention; [Diagram 2] A diagram showing examples of risk assessment positions and collision risk values ​​in a situation where the own ship is selected as the first ship. [Diagram 3] FIG. 13 is a conceptual diagram illustrating a method for estimating a collision risk value at a position other than the risk assessment position. [Figure 4] FIG. 4 is a diagram showing an example of a risk map generated by a risk map generating unit. [Diagram 5] A diagram showing examples of risk assessment positions and collision risk values ​​in a situation where another ship is selected as the first ship. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the electrical configuration of a ship maneuvering assistance device 1 according to an embodiment of the present invention.

[0030] A ship-steering assistance device (ship monitoring device) 1 of this embodiment shown in FIG. 1 is provided on a ship moving on the water, and displays information such as the movements of other ships.

[0031] A display device 3 is connected to the ship-steering assistance device 1. The display device 3 is configured as, for example, a liquid crystal display, and displays information to assist ship-steering. The ship-steering assistance device 1 generates display data for displaying appropriate information on the display device 3, and outputs the data to the display device 3. The display data generated by the ship-steering assistance device 1 includes information on the position and speed of the ship itself, and information on the positions and speeds of other ships. The display data also includes a risk map showing information on locations where there is a high probability of collision between ships.

[0032] The risk map is created based on points with a high probability of collision and an evaluation value of the collision probability, which are obtained using a method similar to OZT. OZT shows an area on the planned course of the other ship (second ship) where the ship (first ship) will be obstructed by the other ship when the ship changes course. However, in this invention, OZT, which evaluates the possibility of collision between the ship and the other ship, is extended to the relationship between the other ship and the ship, or the relationship between the other ship and the other ship. Therefore, the first ship can be either the ship or the other ship, and the second ship can be either the ship or the other ship.

[0033] This ship steering assistance device 1 includes a ship data acquisition unit (information acquisition unit) 11, a target ship selection unit (ship designation unit) 21, a risk assessment position calculation unit 31, a collision risk calculation unit 41, a risk map generation unit 51, and a display data generation unit 61.

[0034] More specifically, the ship maneuvering assistance device 1 is configured as a known computer and includes a CPU, ROM, RAM, etc. The ROM stores a program for generating display data for the risk map. The above hardware and software work together to enable the ship maneuvering assistance device 1 to operate as a ship data acquisition unit 11, a target ship selection unit 21, a risk assessment position calculation unit 31, a collision risk calculation unit 41, a risk map generation unit 51, a display data generation unit 61, etc.

[0035] The ship data acquisition unit 11 acquires necessary data regarding the ship itself and other ships around the ship itself. This data includes information regarding the position and speed of the ship (navigation information).

[0036] Specifically, a GNSS positioning device (not shown) is connected to the ship steering assistance device 1. The ship data acquisition unit 11 can acquire the ship's position based on the positioning result input from the GNSS positioning device. The ship data acquisition unit 11 can also acquire the ship's speed by calculating the change in position obtained from the GNSS positioning device.

[0037] In addition, a radar device (not shown) that detects the surroundings of the ship and generates a radar image is connected to the ship maneuvering assistance device 1. This radar device has a target tracking (TT) function, which is a technology that detects and tracks the movement of detected targets (other ships). The TT function is well known, so to briefly explain it, the TT function calculates the positions and speed vectors of targets (other ships) that exist around the ship based on the progress of past radar images.

[0038] The radar device acquires the relative position and speed of other ships with respect to the ship itself as a reference, but the position and speed vectors of other ships input to the ship data acquisition unit 11 are converted in advance to be ground-based based on the ship's position and heading obtained by appropriate means (for example, the above-mentioned GNSS positioning device and a direction sensor, not shown).

[0039] When generating a risk map, the target ship selection unit 21 selects, between the own ship and other ships, which ship's course change is assumed and the possibility of collision is considered (i.e., which ship is to be the above-mentioned first ship).

[0040] If the helmsman, who is the user of the ship maneuvering assistance device 1, does not specify anything, the ship's own ship is selected as the default first ship. Therefore, the risk map generated will show the possibility of collision between the ship's own ship and another ship. However, the helmsman can also generate a risk map based on the other ship by specifying the desired other ship while looking at the screen of the display device 3. The operation can be performed using an input operation device (e.g., a joystick or trackball, etc.) not shown in the figure that the display device 3 is provided with, or an input operation device connected to the ship maneuvering assistance device 1 can also be used.

[0041] Fig. 2 shows an example of the positions of the own ship 5 and four other ships 6, 7, 8, and 9 input to the ship data acquisition unit 11. In Fig. 2, the positions of the own ship 5 and the other ships 6, 7, 8, and 9 are indicated by arrows showing their respective velocity vectors.

[0042] The following describes a case where the own ship 5 is selected as the first ship by the target ship selection unit 21. Therefore, the other ships 6, 7, 8, and 9 correspond to the second ships.

[0043] The risk assessment position calculation unit 31 in Fig. 1 calculates a risk assessment position by predicting the future position of the second ship that constrains the movement of the first ship between the first ship and the second ship. The risk assessment position is determined to coincide with the position of the second ship at a future time, and serves as a positional reference for evaluating the risk of collision between the first ship and the second ship.

[0044] When predicting the future position of the second vessel, the risk assessment position calculation unit 31 assumes that the second vessel will move from its current position while maintaining a constant course and vessel speed. Therefore, the predicted future position of the second vessel will be aligned along the planned course of the second vessel.

[0045] The risk assessment position calculation unit 31 determines multiple risk assessment positions at appropriate intervals along the estimated planned course for the second vessel, and outputs information specifying each risk assessment position to the collision risk calculation unit 41 and the risk map generation unit 51. The risk assessment position calculation unit 31 also determines the scheduled time for the second vessel to arrive at the risk assessment position, and outputs this scheduled time to the collision risk calculation unit 41. In Figure 2, examples of risk assessment positions determined by the risk assessment position calculation unit 31 for each of the second vessels (other vessels 6, 7, 8, 9) are shown by small circles.

[0046] The collision risk calculation unit 41 in Figure 1 calculates a collision risk value that predicts the risk of collision between the first vessel and the second vessel at each risk assessment position input from the risk assessment position calculation unit 31.

[0047] A more detailed explanation is given below. First, the collision risk calculation unit 41 obtains the estimated time that the first vessel will arrive at the risk assessment position obtained by the calculation of the risk assessment position calculation unit 31. At this time, the risk assessment position calculation unit 31 assumes that the first vessel will change course toward the risk assessment position at the current time and move while maintaining the same vessel speed as before the change of course. In addition, the collision risk calculation unit 41 receives the estimated time that the second vessel will arrive at the risk assessment position from the risk assessment position calculation unit 31.

[0048] In this embodiment, it is considered that a collision occurs when the second vessel arrives at the risk assessment position at the same time as the first vessel arrives at the risk assessment position. However, taking into account the error in the vessel speeds of the first vessel and the second vessel input to the ship maneuvering assistance device 1, the probability density distribution of the time when the first vessel arrives at the risk assessment position and the probability density distribution of the time when the second vessel arrives follow normal distributions centered on their respective scheduled arrival times. Therefore, the probability that the first vessel and the second vessel arrive at the risk assessment position at the same time can be obtained by time integrating the product of the above two probability density distributions.

[0049] The collision risk calculation unit 41 outputs the value obtained by the integration as a collision risk value to the risk map generation unit 51. The numerical values ​​given near the risk evaluation positions in Fig. 2 indicate examples of collision risk values ​​calculated by the collision risk calculation unit 41 for those risk evaluation positions. However, numerical values ​​are omitted for risk evaluation positions where the calculated collision risk value is substantially zero.

[0050] The risk map generating unit 51 generates a risk map, which is information for supporting a vessel operator. The risk map generating unit 51 outputs the generated risk map to the display data generating unit 61.

[0051] A risk map is a two-dimensional distribution of collision risk values ​​that are estimated by interpolating or extrapolating the collision risk value at other positions from the collision risk value at the risk assessment position. The risk map can be created by estimating collision risk values ​​at positions other than the risk assessment position so that the influence of the collision risk value at the risk assessment position decreases monotonically with distance from the risk assessment position.

[0052] In this embodiment, the risk map generating unit 51, as shown in Fig. 3, estimates the collision risk value by arranging isotropic two-dimensional Gaussian distributions weighted according to the risk assessment value with each risk assessment position as the center and adding them up. With this method, it is possible to obtain the collision risk value around each risk assessment position (for example, the collision risk value at the position between two risk assessment positions) by interpolation, with each risk assessment position as the reference. Fig. 3 shows an example in which two risk assessment positions and their collision risk values ​​in Fig. 2 are extracted and two corresponding Gaussian distributions are added up (convoluted).

[0053] The method of fitting a kernel function to each of the points where values ​​are obtained and superimposing the arranged functions is called the kernel method. By using this method, it is possible to obtain a smoothly changing collision risk value at positions other than the risk evaluation position.

[0054] In this embodiment, a Gaussian function is used as the kernel function, which allows the error of the risk assessment position obtained by the risk assessment position calculation unit 31 to be appropriately taken into consideration.

[0055] The risk map may be obtained by other estimation methods, for example, the collision risk values ​​at positions other than the risk assessment positions may be estimated by the well-known inverse distance weighted interpolation method.

[0056] 1 generates display data for displaying the risk map input from the risk map generation unit 51 on the display device 3. The display data generation unit 61 outputs the generated display data to the display device 3 via an appropriate interface.

[0057] Figure 4 shows an example of a risk map corresponding to the situation in Figure 2 displayed on the display device 3. By referring to such a risk map, the ship operator can intuitively distinguish between areas where the risk of collision between the first vessel (own vessel 5) and the second vessel (other vessels 6, 7, 8, 9) is high and areas where the risk is low.

[0058] For convenience of illustration in Figure 4, areas with high collision risk values ​​are shown with narrow hatching, and areas with low collision risk values ​​are shown with wide hatching or no hatching. In Figure 4, the width of the hatching changes stepwise, but on an actual display screen, the collision risk value changes smoothly in response to changes in position, and the color also changes smoothly.

[0059] Since the risk of collision is uncertain, the area of ​​high risk of collision cannot be clearly delimited by a shape such as a circle as in the conventional OZT display, and its outline is inherently unclear. In this respect, the risk map of this embodiment can express such ambiguity of the boundary by a smooth change in color (a change via intermediate colors). Therefore, it is possible to realize a display that is highly compatible with the general sense that a ship operator has regarding the risk of collision.

[0060] On the actual display screen, areas with a high collision risk are shown in red, and areas with a low collision risk in black. However, the colors can be assigned arbitrarily, and for example, as used in thermography, the colors can be assigned in order of increasing collision risk value in a smooth transition from red to yellow, green, light blue, blue, and black. In this case, a known heat map display can be realized.

[0061] As described above, in this embodiment, the target ship selection unit 21 can change which ship is to be the above-mentioned first ship. When the ship navigator of the first ship 5 operates the ship maneuvering assistance device 1 and selects the other ship 7 as the reference (first ship) for calculating the risk assessment position and collision risk value, the risk assessment position and collision risk will be, for example, as shown in Figure 5. As a result, although not shown, the generated risk map will also be different from the example in Figure 4. By displaying a risk map based on the other ship 7, it becomes easier for the ship navigator of the first ship 5 to predict the future course of the other ship 7.

[0062] The distributions of collision risk values ​​shown in Figures 2 and 5 can be easily synthesized by addition. The risk map generating unit 51 can calculate the distribution of collision risk values ​​while switching the selection of the first ship one by one among the own ship 5 and other ships 6, 7, 8, 9 shown in Figure 2, and generate a risk map (synthetic risk map) based on the results of synthesizing all of them. This synthetic risk map also takes into account the risk of collision between the other ships 6, 7, 8, 9 and the other ships 6, 7, 8, 9. Places displayed in red on the synthetic risk map indicate that there is a high possibility of congestion occurring in the future, which is useful information for maneuvering the own ship 5.

[0063] In the above embodiment, the ship maneuvering assistance device 1 is provided on a ship (own ship 5). However, a device having the same configuration as the ship maneuvering assistance device 1 can also be used as a port monitoring device installed in a land facility to monitor ships passing through a port. Although there is no concept of own ship / other ship in the port monitoring device, for example, by selecting one ship from multiple ships in the target ship selection unit 21, a risk map based on that ship can be displayed. In addition, by displaying the above-mentioned composite risk map, the monitor can easily understand areas in the port where congestion is likely to occur in the future.

[0064] As described above, the ship maneuvering assistance device 1 of this embodiment includes a risk map generation unit 51 and a display data generation unit 61. When a position on a planned course estimated for a second ship (e.g., own ship 5) is defined to assess the risk of a first ship colliding with another second ship (e.g., other ships 6, 7, 8, 9) assuming a course change of the first ship, the risk map generation unit 51 estimates the possibility of collision between the first ship and the second ship at positions other than the risk assessment position, and generates a risk map showing the distribution of the estimated possibility of collision. The display data generation unit 61 generates display data for displaying the risk map.

[0065] This allows the ship's operator to intuitively understand the possibility of a collision between the first and second vessels over a wider area than with conventional OZT, by using a risk map that estimates the possibility of a collision with the second vessel when the first vessel changes course, even at locations different from the risk assessment location.

[0066] Although the preferred embodiment of the present invention has been described above, the above configuration can be modified, for example, as follows.

[0067] The position and speed of other ships can also be obtained using an AIS device instead of the TT function of a radar device.

[0068] The kernel function used by the risk map generating unit 51 is arbitrary, and a known kernel function such as a cos function can be used instead of the above-mentioned Gaussian distribution.

[0069] The collision risk value at the risk assessment position may be any value that can evaluate the magnitude of the risk of collision, and may be obtained by methods other than integrating the collision probability distribution. For example, the time at which the second vessel arrives at the risk assessment position may be calculated, and a circle (prediction circle) showing the predicted position of the first vessel at that time may be calculated, and the minimum distance between the risk assessment position and the prediction circle may be calculated as the collision risk value.

[0070] In the above embodiment, the risk assessment position calculation unit 31 determines a plurality of risk assessment positions so that they are spaced at appropriate intervals along the planned course of the second vessel. However, the risk assessment position calculation unit 31 may determine the risk assessment position on the planned course of the second vessel using a different method. For example, the risk assessment position calculation unit 31 may determine the intersection of the trajectory of collision prediction points where a collision may occur in the future, which is calculated from the positions and vessel speeds of the first vessel and the second vessel (in other words, the speed ratio between the first vessel and the second vessel), and the planned course of the second vessel, as the risk assessment position. This trajectory of collision prediction points is known as the Line of Predicted Collision (LOPC).

[0071] The risk assessment position calculation unit 31 may determine a risk assessment position on the planned course of the other ship using DCPA or TCPA calculated from the position and speed of the first ship and the position and speed of the second ship.

[0072] A publicly known document (Imazu Hayama: OZT calculation method using collision course, Journal of the Japan Society of Navigation, NAVIGATION, vol. 188, pp. 78-81, April 2014.) discloses a method for easily calculating OZT as a line segment on the planned route of the other ship. This method can be considered to evaluate whether or not the possibility of collision is at a predetermined level or higher at every position (risk evaluation position) on the planned route of the other ship. When calculating OZT using the above calculation method, the risk map generation unit 51 defines a mesh of a certain size to divide the area around the own ship (first ship), and calculates the number of other ships (second ships) that include the above-mentioned OZT line segment for each mesh. Furthermore, when the above-mentioned number is placed as a value at the center position of each mesh, the risk map generation unit 51 calculates the value at the position between the centers of adjacent meshes by two-dimensional interpolation calculation. This makes it possible to generate a risk map showing the distribution of estimated collision possibilities with another ship (second ship) at locations other than the planned route.

[0073] The display may be configured so that a user can switch between the risk map display and the circular OZT display as in Non-Patent Document 1. In the ship maneuvering assistance device 1, by displaying the OZT using a circle with a ship other than the ship as a reference (first ship), it is possible to provide the user with useful information. The circular OZT display and the risk map may be displayed simultaneously, overlapping each other.

[0074] When creating a risk map, the range of spatial influence of the collision risk value at each risk assessment position (in other words, the so-called bandwidth in the kernel function) may be a fixed value, but may also be configured to be changeable by the user. [Explanation of symbols]

[0075] 1. Ship steering support device (ship monitoring device) 11 Ship data acquisition unit (information acquisition unit) 41 Collision risk calculation unit 51 Risk map generation unit

Claims

1. a risk map generating unit which, when a position on a planned course estimated for a second ship among a plurality of ships is called a risk assessment position, which is determined in order to assess the risk of a collision between the first ship and another second ship assuming a course change of the first ship, estimates a collision risk value between the first ship and the second ship at a position other than the risk assessment position based on the collision risk value between the first ship and the second ship at the risk assessment position, and generates a risk map showing a distribution of the estimated collision risk values; a display data generating unit that generates display data for displaying the risk map; A ship monitoring device comprising:

2. 2. The vessel monitoring device according to claim 1, The risk map generation unit estimates the collision risk value at positions other than the risk assessment position using a function that can interpolate the surrounding collision risk values ​​based on the risk assessment position, and generates a risk map showing the distribution of the estimated collision risk values.

3. The vessel monitoring device according to claim 2, A ship monitoring device characterized in that the risk map generation unit generates the risk map by adding up kernel functions centered on each of the risk evaluation positions.

4. The vessel monitoring device according to claim 3, The vessel monitoring device is characterized in that the kernel function is a Gaussian function.

5. The vessel monitoring device according to any one of claims 1 to 4, A ship monitoring device comprising a ship designation unit capable of selecting and designating the first ship from the plurality of ships.

6. The vessel monitoring device according to claim 5, Provided on ships, A ship monitoring device characterized in that the ship designation unit is capable of designating another ship around the ship itself as the first ship.

7. The vessel monitoring device according to any one of claims 1 to 6, Provided on ships, A ship monitoring device characterized in that the risk map generation unit is capable of generating the risk map when the first ship and the second ship are both other ships surrounding the own ship.

8. The vessel monitoring device according to any one of claims 1 to 5, A ship monitoring device characterized in that it is installed in a land facility.

9. A vessel monitoring device according to any one of claims 1 to 8, A ship monitoring device characterized in that the risk map generation unit generates the risk map by synthesizing the distribution of the collision risk values ​​when each of a plurality of ships is regarded as the first ship.

10. By a computer, When a position on a planned course estimated for a second vessel, which is determined in order to assess a risk of a first vessel colliding with another second vessel assuming a course change of the first vessel among a plurality of vessels, is called a risk assessment position, a collision risk value between the first vessel and the second vessel at a position other than the risk assessment position is estimated based on the collision risk value between the first vessel and the second vessel at the risk assessment position; generating a risk map indicating a distribution of the estimated collision risk values; generating display data for displaying the risk map; Ship monitoring methods.

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