High latitude chart projection selection and switching method

Abstract

The application belongs to the technical field of computer information processing, and specifically discloses a high-latitude sailing chart projection selection and switching method. The application solves the problems of projection selection, coordinate system adaptation and switching link fragmentation in high-latitude sailing through a coherent technical path based on latitude selection projection, automatic coordinate system matching, switching judgment according to sailing state and smooth conversion execution. The application realizes the standardized selection of projection based on geographical latitude as an objective basis, overcoming the blindness of experience selection. Through automatic matching of projection and coordinate system, the problem of disconnection with the navigation system and the need for manual intervention is solved. By introducing a switching area and dynamically judging the timing according to real-time sailing information, the rigid boundary switching is transformed into a smooth transition linked with the sailing state. Finally, multiple isolated operations are integrated into a complete process driven by data and automatically connected, significantly improving the automation level, system adaptability and navigation reliability of high-latitude sailing.

Description

Technical Field

[0001] This application belongs to the field of computer information processing technology, specifically relating to the method of selecting and switching high-latitude nautical chart projections. Background Technology

[0002] Current high-latitude nautical chart technology focuses primarily on improving single projections, with unclear definitions of high-latitude nautical chart coordinate systems. Some scholars use a mix of three-dimensional grid coordinate systems and planar grid projections in their descriptions of high-latitude grid coordinate systems, failing to comprehensively analyze the characteristics and applicable scope of different high-latitude nautical chart projections and construct a suitable scheme corresponding to a nautical chart projection and coordinate system. There is no clear solution to the problem of switching projections from low to high latitudes.

[0003] It is worth noting that high-latitude nautical charts often require special map projections to overcome the distortions inherent in high-latitude nautical charts. However, the selection of chart projections relies heavily on the experience of navigators, leading to the following problems: First, it is disconnected from navigation systems. The choice of chart projection is not linked to the nautical chart coordinate system used by the ship's navigation system. After changing charts, manual adjustments or reconfiguration of the navigation system are required, which is cumbersome and prone to errors. Second, the selection criteria are unscientific. There is a lack of quantitative and objective comparative data on projection characteristics, resulting in a somewhat arbitrary selection that may lead to charts with excessive distortion or unsuitability for current navigation methods. Finally, the chart switching process is abrupt. When switching from traditional nautical charts to high-latitude charts, the sudden change in navigation parameters can cause display confusion and parameter abrupt changes, lacking a smooth transition mechanism.

[0004] Therefore, there is an urgent need for a complete solution that covers everything from selecting the nautical chart coordinate system to selecting the nautical chart projection and then switching the nautical chart projection. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for selecting and switching high-latitude nautical chart projections. This method aims to solve the problem that existing technologies are limited by the isolated and static processing of the three elements of high-latitude nautical chart projection, nautical chart coordinate system, and navigation status. As a result, when navigating from low latitudes to high latitudes, there is a technical problem that the process of automatically and continuously completing the scientific decision-making of projection, coordinate system adaptation, and smooth state-driven switching cannot be achieved.

[0006] The first aspect of this application relates to a method for selecting and switching high-latitude nautical chart projections, comprising: step S10, determining a target nautical chart projection from a variety of predefined nautical chart projections based on the geographical latitude of the target navigation area; step S20, determining a nautical chart coordinate system matching the target nautical chart projection based on the type of the target nautical chart projection; step S30, when the navigation vehicle enters a preset high-latitude switching area during navigation, determining whether a nautical chart coordinate system switching opportunity has been reached based on the real-time navigation information of the navigation vehicle; and step S40, when it is determined that a nautical chart coordinate system switching opportunity has been reached, performing a conversion between the target nautical chart coordinate system and the original nautical chart coordinate system based on a preset coordinate system transformation relationship.

[0007] In one embodiment, step S10 includes: acquiring at least one geographic coordinate point within the target navigation area; determining the target latitude interval to which the target navigation area belongs from a first latitude interval, a second latitude interval, or a third latitude interval based on the latitude of the geographic coordinate point, wherein the upper limit latitude of the first latitude interval is lower than the lower limit latitude of the second latitude interval, and the upper limit latitude of the second latitude interval is lower than the lower limit latitude of the third latitude interval; and determining the target nautical chart projection based on a preset correspondence between the target latitude interval and multiple nautical chart projections.

[0008] In one embodiment, before step S10, the method further includes: establishing a multi-dimensional characteristic evaluation model for various nautical chart projections, wherein the multi-dimensional characteristic evaluation model includes at least evaluation dimensions for angular distortion, length distortion, the degree of approximation between meridians and straight lines, and the degree of approximation between great circle routes and straight lines; evaluating the applicability of different nautical chart projections in different latitude ranges based on the multi-dimensional characteristic evaluation model; and establishing a preset correspondence between latitude ranges and nautical chart projections based on the evaluation results.

[0009] In one embodiment, step S30 includes: step S31, setting a switching latitude and a transition latitude interval, wherein the transition latitude interval is a continuous region extending to both sides of a preset latitude difference with the switching latitude as the center; step S32, when the current position latitude of the navigation vehicle is detected to enter the transition latitude interval, obtaining the heading of the navigation vehicle; step S33, based on the relative positional relationship between the heading of the navigation vehicle and the boundary latitude of the transition latitude interval, determining whether a preset switching trigger condition is met.

[0010] In one embodiment, step S32 specifically involves: when the current latitude of the navigation vehicle is detected to enter the transition latitude range for the first time, obtaining the first entry heading of the navigation vehicle.

[0011] In one embodiment, step S33 specifically involves: if the vehicle enters from the low latitude side outside the transition latitude interval and the first entry heading points to the latitude switch, then it is determined that the switching opportunity from the original nautical chart coordinate system to the target nautical chart coordinate system has been reached at the current position; if the vehicle exits from the high latitude side within the transition latitude interval, then it is determined that the switching opportunity from the target nautical chart coordinate system to the original nautical chart coordinate system has been reached when the vehicle exits the transition latitude interval.

[0012] In one embodiment, step S40 includes: determining the first coordinate system parameters corresponding to the target nautical chart projection and the second coordinate system parameters corresponding to the original nautical chart projection; acquiring the first coordinate data of the navigation vehicle in the original nautical chart coordinate system corresponding to the switching timing; calling the coordinate transformation formula corresponding to the type of the target nautical chart projection and the original nautical chart projection, and combining the first coordinate system parameters and the second coordinate system parameters to convert the first coordinate data into the second coordinate data in the target nautical chart coordinate system.

[0013] In one embodiment, after step S40, the method further includes: providing second coordinate data to the navigation system so that the navigation system displays and plots navigation elements on a nautical chart using the target nautical chart projection based on the second coordinate data.

[0014] The second aspect of this application relates to a device for selecting and switching nautical chart projections, comprising: a projection determination module, used to determine a target nautical chart projection from a variety of predefined nautical chart projections based on the geographical latitude of the target navigation area; a coordinate system determination module, used to determine a nautical chart coordinate system matching the target nautical chart projection based on the type of the target nautical chart projection; a switching timing judgment module, used to determine whether a nautical chart coordinate system switching timing has been reached based on the real-time navigation information of the navigation vehicle when the navigation vehicle enters a preset high-latitude switching area during navigation; and a coordinate transformation module, used to perform a transformation between the target nautical chart coordinate system and the original nautical chart coordinate system based on a preset coordinate system transformation relationship when it is determined that a nautical chart coordinate system switching timing has been reached.

[0015] Thirdly, this application provides a nautical chart processing device, comprising: at least one memory for storing a program; and at least one processor for executing the program stored in the memory, wherein when the program stored in the memory is executed, the processor is used to execute the method described in the first aspect or any possible implementation thereof.

[0016] Fourthly, this application provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to perform the method described in the first aspect or any possible implementation thereof.

[0017] Fifthly, this application provides a computer program product that, when run on a processor, causes the processor to perform the method described in the first aspect or any possible implementation thereof.

[0018] It is understood that the beneficial effects of the second to fifth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0019] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: This application systematically solves the core problems in the prior art by adopting a coherent automated technical path that selects projection based on geographical latitude, automatically matches the corresponding coordinate system, determines the switching time based on the navigation status, and finally performs a smooth conversion.

[0020] Specifically, firstly, by using objective and quantifiable data such as geographical latitude as the initial decision-making basis for projection selection, the previous reliance on blind human experience was changed, providing a scientific and standardized decision-making foundation for projection selection. Based on this decision, by establishing inherent matching rules between projection type and nautical chart coordinate system, automatic and deep coupling between projection and coordinate system was achieved, thereby eliminating the disconnect between navigation system and nautical chart in terms of coordinate reference and avoiding the tedious and error-prone manual adaptation process.

[0021] Furthermore, this application does not perform a rigid, one-size-fits-all switch at fixed latitude boundaries. Instead, it introduces the concept of a high-latitude switching region and dynamically determines the switching timing based on the carrier's real-time navigation information. This links the switching behavior to the carrier's actual navigation state, transforming it from a passive, abrupt response into an active, state-driven decision. Finally, a coordinate system transformation is performed based on a preset transformation relationship, ensuring the smoothness and data continuity of the entire switching process.

[0022] Therefore, this application integrates multiple previously isolated, manual, and error-prone operational steps into a complete closed-loop process based on objective data, with automatic connection between preceding and subsequent steps and smooth transition according to the navigation situation, thereby fundamentally improving the automation level, system adaptability, and navigation reliability of nautical chart application in high-latitude navigation. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the method for selecting and switching high-latitude nautical chart projections provided in the embodiments of this application; Figure 2 This is a schematic diagram of the Northern Hemisphere of the polar spherical grid coordinate system provided in the embodiments of this application; Figure 3 This is a schematic diagram of the Southern Hemisphere of the polar spherical grid coordinate system provided in the embodiments of this application; Figure 4 This is a schematic diagram of the horizontal geographic coordinate system provided in the embodiments of this application; Figure 5 This is a schematic diagram of the transverse latitude line provided in the embodiments of this application; Figure 6 This is a flowchart illustrating the process of determining the switching time provided in an embodiment of this application; Figure 7 This is a schematic diagram of the high-latitude nautical chart projection selection and switching device provided in the embodiments of this application; Figure 8 This is a schematic diagram of the structure of the nautical chart processing equipment provided in the embodiments of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A existing alone, A and B existing simultaneously, and B existing alone. In this application, the symbol " / " indicates that the related objects are in an "or" relationship, for example, A / B means A or B.

[0026] In this application, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order of objects. For example, "first response message" and "second response message," etc., are used to distinguish different response messages, not to describe a specific order of response messages.

[0027] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0028] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0029] Currently, high-latitude navigation faces challenges such as difficulty in selecting nautical chart projections, mismatch between nautical chart projections and coordinate systems, and difficulties in switching between the two. There is an urgent need to provide a complete solution that covers everything from selecting a nautical chart coordinate system to selecting a nautical chart projection and then switching between nautical chart projections.

[0030] Based on this, this application proposes an embodiment of a method for selecting and switching high-latitude nautical chart projections. Please refer to... Figure 1 , Figure 1 This is a flowchart illustrating the method for selecting and switching high-latitude nautical chart projections provided in this embodiment. In this embodiment, the method includes steps S10 to S40.

[0031] Step S10: Determine the target nautical chart projection from a variety of predefined nautical chart projections based on the geographical latitude of the target navigation area.

[0032] Step S20: Determine the nautical chart coordinate system that matches the target nautical chart projection based on the type of the target nautical chart projection.

[0033] Step S30: When the navigation vehicle enters the preset high-latitude switching area during navigation, determine whether the timing for switching the nautical chart coordinate system has been reached based on the real-time navigation information of the navigation vehicle.

[0034] Step S40: When it is determined that the time for switching the nautical chart coordinate system has arrived, a conversion is performed between the target nautical chart coordinate system and the original nautical chart coordinate system based on the preset coordinate system conversion relationship.

[0035] It should be noted that step S10 establishes the objective basis for projection selection. Its core lies in establishing a latitude-projection mapping rule to replace the traditional subjective selection based on the experience of navigators. The predefined nautical chart projection refers to a set of mathematical projection models pre-built into the system to meet the characteristics of high-latitude navigation. This set of models may include, but is not limited to: sundial projection, equidistant tangent cylindrical projection, polar spherical projection, and Mercator projection for mid- and low-latitude regions.

[0036] It should be noted that determining this operation based on geographical latitude can be achieved by the latitude interval matching algorithm in the navigation planning system. This algorithm uses a preset latitude threshold as a decision node, inputs the center latitude or maximum latitude of the target navigation area, and automatically outputs the recommended target projection type. For example, when the system identifies a navigation area with a latitude higher than 75°, the algorithm will automatically select the sundial projection, as it can project great circle routes as straight lines, greatly facilitating the shortest route planning in polar regions. This step eliminates the uncertainty of projection selection, providing a theoretically optimal cartographic basis for high-latitude navigation and ensuring the geometric correctness of subsequent route planning.

[0037] It should be noted that step S20 resolves the mismatch between the projection and the underlying coordinate system data, which is crucial for ensuring the spatial accuracy of nautical charts. A nautical chart coordinate system is a mathematical benchmark describing geographic spatial location. Matching refers to specifying a unified and accurate geodetic benchmark for the nautical chart data generated or used for the target projection. This step can be achieved by a projection-coordinate system association table built into the electronic chart display and information system. This table defines recommended coordinate systems for different projection application scenarios. For example, for polar charts used in international navigation, a sundial projection associated with the WGS84 coordinate system is often used; for high-latitude charts along the Chinese coast, the CGCS2000 coordinate system is associated. After selecting a projection in step S10, the system queries this table and automatically locks the corresponding coordinate system standard.

[0038] Understandably, step S20 ensures from the data source that the geographic coordinates of the chart elements are strictly consistent with the mathematical framework of the selected projection, avoiding positional deviations of tens to hundreds of meters caused by different benchmarks, and fundamentally eliminating the risk of grounding or stranding caused by this.

[0039] It should be noted that step S30 realizes the transition from continuous navigation to discrete switching decisions, and its innovation lies in making the switching process intelligent and refined. The high-latitude switching area is a geographical range pre-defined based on projection distortion theory and navigation practice, such as a strip area at 84° latitude, serving as a buffer zone for the transition from Mercator projection to high-latitude projection. Real-time navigation information is provided by shipboard positioning sensors (such as GNSS receivers), attitude sensors (such as gyrocompasses), and navigation status sensors (such as logs), specifically including data such as latitude and longitude, heading, and speed.

[0040] It should be noted that the process of determining the switching timing is executed by a switching timing determination module, which analyzes based on preset logical conditions. For example, these conditions can be set, but are not limited to: the vessel maintaining a stable course and speed within the switching area for more than a predetermined time (e.g., 5 minutes), and the GNSS positioning signal quality being good. The effect of this step is to link the switching action to the ship's stable navigation state, avoiding display confusion and crew misjudgment that might occur during sharp turns, maneuvers, or poor signal conditions, making the switching process safer and smoother.

[0041] It should be noted that step S40 is the execution stage of the switching action, the core of which is to complete the seamless conversion of the spatial reference, ensuring the continuity of all spatial information such as the ship's position and route in the display. The preset coordinate system transformation relationship refers to the transformation parameters calculated through a rigorous mapping model, such as the seven-parameter Bursa model parameters used for conversion between WGS84 and CGCS2000. The conversion is implemented by the real-time dynamic coordinate transformation engine in the kernel of the electronic chart system. After receiving the switching command, the engine immediately calls the corresponding transformation parameters to perform batch and rapid mathematical transformations on the coordinates of all dynamic targets (the ship itself) and static chart elements in the current display view, and completes the screen update within one display refresh cycle.

[0042] As an alternative, for scenarios that do not involve conversion between different geodetic bases but only switching between different projections under the same base, this step is converted into a projection transformation, that is, using the forward and inverse solution algorithms between the Mercator projection formula and the sundial projection formula to calculate coordinates. The direct technical effect of this step is that it achieves a smooth transition between the chart display background and the spatial base of the positioning information without the crew's noticeable perception. The position of the ship's symbol on the chart does not change abruptly, and the route remains continuous, thereby ensuring the continuity of navigational surveillance and the consistency of decision-making, and improving the overall safety of navigation in complex high-latitude sea areas.

[0043] Therefore, this application integrates multiple previously isolated, manual, and error-prone operational steps into a complete closed-loop process based on objective data, with automatic connection between preceding and subsequent steps and smooth transition according to the navigation situation, thereby fundamentally improving the automation level, system adaptability, and navigation reliability of nautical chart application in high-latitude navigation.

[0044] Furthermore, this application provides feasible implementation methods for each step.

[0045] It should be noted that the core of step S10 lies in how to establish a preset correspondence between latitude intervals and nautical chart projections, that is, a predefined nautical chart projection.

[0046] In one feasible implementation, before step S10, the method further includes: establishing a multi-dimensional characteristic evaluation model for various nautical chart projections, wherein the multi-dimensional characteristic evaluation model includes at least evaluation dimensions for angular distortion, length distortion, the degree of approximation between meridians and straight lines, and the degree of approximation between great circle routes and straight lines; evaluating the applicability of different nautical chart projections in different latitude ranges based on the multi-dimensional characteristic evaluation model; and establishing a preset correspondence between latitude ranges and nautical chart projections based on the evaluation results.

[0047] It is understandable that, after projection, all elements of a high-latitude nautical chart should maintain a similarity to the actual terrain and have simple meridian lines to facilitate chart production and meet the needs of measuring angles, distances, determining the geographical coordinates of points, depicting routes, and plotting navigation conditions. Based on the accuracy required for chart use and the convenience of chart operations, a suitable high-latitude nautical chart projection should be selected. The criteria for selecting a high-latitude nautical chart projection are as follows: a) The use of conformal projection facilitates angle measurement on nautical charts.

[0048] b) The length and area distortions meet the requirements for nautical chart compilation, the scale of the entire chart is uniform, and it is convenient for accurate measurement of distance and area.

[0049] c) The latitude and longitude grid is simple, and the longitude lines are projected as straight lines, which makes it easy to construct the grid, measure the heading, and also easy to use in conjunction with special navigation methods in high latitudes such as grid navigation.

[0050] d) Great circle routes are straight or as close to straight as possible, so that great circle routes can be used for navigation at high latitudes.

[0051] Therefore, the multi-dimensional characteristic evaluation model should include at least the evaluation dimensions of angular deformation, length deformation, the degree of approximation between meridians and straight lines, and the degree of approximation between great circle routes and straight lines.

[0052] In practical applications, a multi-dimensional characteristic evaluation model can be a comprehensive evaluation system composed of a series of mathematical indicators and algorithms. Specifically: The angular distortion assessment dimension refers to the difference between the angle between any two directions at any point after projection and the corresponding angle on the ground. This dimension is quantified by calculating the maximum angular distortion value (ω). For navigation operations that require precise bearing measurements, the smaller this value, the better. Conformal projections (such as Mercator) score full marks on this dimension.

[0053] The length distortion assessment dimension refers to the ratio of the projected length to the corresponding length on the ground. This dimension is evaluated by calculating the length ratio (μ) and its maximum distortion value within the mapped area. For navigation phases that require estimating distance or determining distance, this distortion should be as small as possible, and equidistant projections perform optimally in this dimension.

[0054] The approximation dimension of a meridian to a straight line assesses whether the projected meridian is a straight line or its deviation from a straight line. In nautical practice, the meridian serves as a direction reference (true north reference). If it is a straight line (such as in the Mercator projection), it facilitates the direct measurement of true bearing on the map. This dimension can be quantified by calculating the meridian curvature or the degree of fit with the reference straight line.

[0055] Great circle routes are the shortest paths between two points on the Earth's surface. The approximation dimension of a great circle route to a straight line assesses how well a great circle route is depicted as a straight line on a projected map. This dimension is crucial for planning long routes across high latitudes or polar regions. For example, sundial projections score full marks on this dimension because they accurately project all great circle routes as straight lines.

[0056] Finally, based on the requirements for selecting nautical chart projections, the high-latitude projection characteristics of polar spherical projection, transverse Mercator projection, and sundial projection based on the Earth's sphere are presented from four aspects: angular distortion, length distortion, degree of approximation between meridians and straight lines, and degree of approximation between great circle routes and straight lines. These are shown in Table 1.

[0057] Table 1. Schematic diagram of different projection characteristics:

[0058] Understandably, Table 1 shows that in terms of conformity, length distortion, regularity of latitude and longitude grids, and the degree of proximity of great circle routes to straight lines, polar spherical projection and transverse Mercator projection are more suitable than other projection methods, and polar spherical projection is slightly better than transverse Mercator projection.

[0059] Understandably, Table 1 illustrates the convenience of using projection methods in conjunction with navigation methods. The polar spherical projection can directly support the high-latitude navigation needs based on the grid coordinate system, and also well accommodate the navigation needs based on the transverse or oblique coordinate system; the transverse Mercator projection can directly support the high-latitude navigation needs based on the transverse coordinate system.

[0060] It should be noted that the process of evaluating and establishing predefined correspondences based on the model is implemented through a projection characteristic simulation and evaluation algorithm. This algorithm takes a geographical latitude interval as input, traverses all predefined projections, and densely samples and calculates the index values ​​of the four dimensions mentioned above within each latitude interval. Subsequently, a multi-objective weighted decision-making module assigns weights to each evaluation dimension based on the core requirements of high-latitude navigation, and calculates the comprehensive applicability score of each projection in each latitude interval.

[0061] Ultimately, the system automatically selects the projection with the highest overall score for each latitude interval, forming a structured table of latitude interval-recommended projection correspondences, which is then embedded in the configuration file of the maritime navigation system. As an alternative, the decision logic can deviate from fixed weights, allowing users to select different evaluation modes based on the specific stage of the voyage, such as ocean planning or coastal navigation, such as shortest distance priority or bearing measurement priority. The system dynamically calls the corresponding weight set for calculation, thereby generating a more mission-adaptive correspondence.

[0062] For example, the high-latitude applicability of the conventional Mercator projection scheme is analyzed.

[0063] It should be noted that the Mercator projection is generally applicable to low and mid-latitude regions, with greater deformation at high latitudes. Through analysis of the deformation of the Mercator projection at high latitudes, it is believed that Mercator projection nautical charts still have certain applicability in areas below or close to 83° north and south latitude. It is recommended to use Mercator projection for paper nautical charts in this range, which is in line with the usage habits of navigation operations.

[0064] It should be noted that when the latitude is between 75° and 85°, the reference latitude is between 75° and 85°, the length distortion range is 5%, 10%, 20%, 30%, 40% and 50% respectively, and the chart sheet size is in both full-sheet horizontal and full-sheet vertical format, the reference latitude, latitude range, scale range and chart sheet format of Mercator nautical charts should be as shown in Tables 2 to 7 below.

[0065] Table 2. Availability of Mercator projection with 5% length deformation:

[0066] Table 3. Availability of Mercator projection when length distortion is within 10%:

[0067] Table 4. Availability of Mercator projection when length distortion is within 20%:

[0068] Table 5. Availability of Mercator projection with a 30% length deformation:

[0069] Table 6. Availability of Mercator projection with 40% length deformation:

[0070] Table 7. Availability of Mercator projection with 50% length deformation:

[0071] It should be noted that when the reference latitude is within the middle latitude of the chart sheet, the maximum length distortion is smaller than when using other reference latitudes. As shown in Tables 2 to 7, a length distortion range of 5% allows for the compilation of nautical charts at scales of 1:200,000 and above; a length distortion range of 10% allows for the compilation of nautical charts at scales of 1:500,000 and above; and a length distortion range of 20% to 50% allows for the compilation of nautical charts at latitudes of 75° to 85° and scales of 1:1,000,000 and above. The latitude ranges and chart sheet formats applicable to the Mercator projection can be found in Table 2. Therefore, by adjusting the position of the reference latitude and determining a reasonable length distortion range, the basic needs for compiling nautical charts at scales of 1:1,000,000 and above, as well as ordinary full-size chart sheets, can be met.

[0072] It is understandable that when a set of nautical charts of the same scale uses a unified reference parallel, and the reference parallel of some chart sheets is not in the middle of the chart sheet, the maximum length distortion on the chart is greater than when the middle parallel of the chart sheet is used as the reference parallel, which limits the applicability of the Mercator projection.

[0073] However, within the latitude range of 75° to 85° and the reference latitude range of 75° to 85°, the maximum length distortion within a 5° to 7° latitude difference near each reference latitude is within 50%, the length distortion within a 3° to 5° latitude difference is within 30%, and the length distortion within a 1° to 2° latitude difference is within 10%. Considering more extreme cases, when the latitude is 75° to 80° and the reference latitude is 75°, the length distortion ranges from 0 to 49.03%; when the latitude is 80° to 85° and the reference latitude is 80°, the length distortion at 84° is 49.65%. The Mercator projection can still meet the needs of compiling nautical charts at different scales of 1:1,000,000 and above within these two latitude ranges.

[0074] If a suitable baseline latitude is selected and the length distortion range is adjusted appropriately, the Mercator projection becomes more valuable when the baseline latitude is not in the middle latitude of the map sheet. Therefore, within the latitude range of 75° to 85°, regardless of whether the baseline latitude is in the middle latitude of the map sheet, by using a reasonable baseline latitude and a reasonable length distortion range, the Mercator projection can still meet the needs of compiling nautical charts of a certain scale and map sheet size.

[0075] Based on research into the charting industry, existing paper nautical charts use the Mercator projection and can be used below 83°N latitude. The Northeast Passage in high latitudes is between 82°N and 83°N. To improve the applicability of traditional Mercator charts and reduce the chart switching steps for general navigation in high latitudes, it is recommended to select 83°N as the boundary for paper nautical charts to use the traditional Mercator projection method.

[0076] Therefore, it can be seen that, based on the characteristics of the nautical chart projection scheme and the type of chart, for navigation areas below or near 83° north and south latitude, such as the Northeast Passage and Northwest Passage, paper nautical charts should use Mercator projection charts to avoid switching between charts with different projection methods. When the navigation area covers the near-polar region of the poles, paper nautical charts should uniformly use polar spherical projection charts.

[0077] At this point, electronic chart navigation systems need to support different nautical chart projection methods and coordinate system conversions. The expression of geographical features on the charts and the nautical calculation methods should be more flexible. High-latitude electronic chart navigation systems should primarily use polar spherical projection nautical charts, while also being compatible with other projection methods such as transverse Mercator projection nautical charts, to flexibly support the application needs of various navigation methods.

[0078] Understandably, this implementation transforms the subjective and vague projection selection process, primarily based on the experience of nautical experts, into an automated and reproducible decision-making process based on objective mathematical indicators and clear rules, thus enhancing the standardization and scientific rigor of the solution. Secondly, by comprehensively considering multiple interdependent projection characteristics, this method can recommend the most comprehensive, rather than the most optimal, projection for a specific navigation mission across different latitude ranges, achieving the best balance between navigation safety and efficiency. Finally, this scientific evaluation and decision-making mechanism serves as a prerequisite, ensuring that the instruction to determine the target projection based on latitude in the subsequent step S10 has a solid technical basis, thereby guaranteeing the reliability and effectiveness of the entire high-latitude navigation projection switching method.

[0079] Therefore, step S10 can be specifically described as follows: obtaining at least one geographic coordinate point within the target navigation area; determining the target latitude interval to which the target navigation area belongs from a first latitude interval, a second latitude interval, or a third latitude interval based on the latitude of the geographic coordinate point, wherein the upper limit latitude of the first latitude interval is lower than the lower limit latitude of the second latitude interval, and the upper limit latitude of the second latitude interval is lower than the lower limit latitude of the third latitude interval; and determining the target nautical chart projection based on the preset correspondence between the target latitude interval and multiple nautical chart projections.

[0080] Understandably, obtaining at least one geographic coordinate point within the target navigation area is the data input step for projection selection. Its purpose is to transform the abstract navigation area into specific latitude values ​​that can be mathematically compared. Geographic coordinate points typically refer to latitude and longitude coordinates, which can be obtained automatically by the navigation planning system.

[0081] In one feasible implementation, the system extracts all waypoints along the user-planned or input route and identifies the waypoint with the highest latitude value as the key criterion. This is because the difficulty of high-latitude projection mainly stems from the significant deformation in high-latitude regions; therefore, selecting the highest latitude point within the region for evaluation ensures the applicability of the chosen projection throughout the entire area. Alternatively, the system can also calculate the coordinates of the geometric center point of the target navigation area. This step transforms the qualitative description of the region into precise, computer-processable numerical values, laying the foundation for subsequent logical judgments.

[0082] Understandably, determining the target latitude interval based on the latitude of the geographical coordinates is the core classification and judgment logic, and its technical essence is the interval matching algorithm. Among them, the first latitude interval, the second latitude interval, and the third latitude interval are latitude zones pre-divided based on projection distortion theory and navigation practice.

[0083] For example, in one specific implementation, the first latitudinal interval (e.g., the mid-to-low latitude region): As mentioned earlier, the Mercator projection is generally applicable to mid-to-low latitude regions, which is the traditional and clearly applicable range; the second latitudinal interval (e.g., the high-latitude transition region): As previously analyzed, in areas below or close to 83° north and south latitude, such as 75° to 85°, by adjusting the baseline latitude and accepting certain length distortions, the Mercator projection can still meet the needs of nautical chart compilation, as detailed in Tables 2 to 7 above. This indicates that within the high latitudes, there exists a sub-region where the Mercator projection is still usable; the third latitudinal interval (e.g., the core polar region): As previously pointed out, when the navigation area covers the near-polar region of the poles, paper nautical charts should uniformly adopt the polar spherical projection. This is the core high-latitude region where a special projection must be switched.

[0084] Understandably, clear standards are needed when computing devices perform calculations. Therefore, we can establish that the upper limit of the first latitude interval is lower than the lower limit of the second latitude interval, and the upper limit of the second latitude interval is lower than the lower limit of the third latitude interval. This allows us to quickly and unambiguously determine the target latitude interval to which the target region belongs. The benefit of this step is that it establishes a clear and stable decision-making path, completely eliminating the subjectivity and ambiguity of human judgment.

[0085] It should be noted that determining the target nautical chart projection, based on the pre-defined correspondence between the target latitude interval and various nautical chart projections, is the output link of the decision-making chain. Its technical implementation relies on a pre-set projection mapping table. This mapping table is the output of the aforementioned multi-dimensional characteristic evaluation model, and it solidifies the correspondence between "latitude interval - recommended projection" in the form of a data structure. For example, the mapping table content could be: key "first latitude interval" corresponds to value "Mercator projection"; key "second latitude interval" corresponds to value "transverse Mercator projection"; key "third latitude interval" corresponds to value "polar spherical projection". Once the system determines the target latitude interval, it retrieves the unique corresponding target nautical chart projection type from this mapping table through a single lookup operation.

[0086] As an alternative, for more complex scenarios, this correspondence may not be a simple static table, but a rule engine that includes additional conditions, such as the type of navigation mission: ocean navigation or coastal navigation, and derives the final projection through rule reasoning.

[0087] Ultimately, this implementation transforms the complex problem of projective selection into an automated data retrieval based on key latitudes, completed in milliseconds. This ensures the immediacy, accuracy, and consistency of projection selection decisions, providing a correct cartographic basis for the safe navigation of ships in high-latitude waters.

[0088] Furthermore, for step S20, it is necessary to clarify the correspondence between the type of nautical chart projection and the nautical chart coordinate system that matches the nautical chart projection.

[0089] It should be noted that the coordinate systems of high-latitude nautical charts include the polar spherical grid coordinate system and the transverse Mercator transverse coordinate system.

[0090] Specifically, please refer to the polar spherical grid coordinate system. Figure 2 and Figure 3 , Figure 2 This is a schematic diagram of the Northern Hemisphere of the polar spherical grid coordinate system provided in the embodiments of this application. Figure 3 This is a schematic diagram of the Southern Hemisphere of the polar spherical grid coordinate system provided in the embodiments of this application.

[0091] Understandably, on high-latitude nautical charts using polar spherical projection, the origin is defined as the North Pole (South Pole). From the origin, along the 0° meridian towards the Pacific Ocean, the grid is 0°G, and towards the Atlantic Ocean, the grid is 180°G (if the origin is the South Pole, then from the origin, along the 0° meridian towards the Pacific Ocean, the grid is 180°G, and towards the Atlantic Ocean, the grid is 0°G). Using this 0° meridian as the grid heading reference, the... The axis is along the 0°G direction of the grid. The axis is established along the 90°G direction of the grid, parallel to the heading datum on the polar spherical chart. The coordinate system is the polar spherical grid coordinate system.

[0092] Specifically, on high-latitude nautical charts using the transverse Mercator projection (transverse Mercator charts), a point on the chart is used as the origin to define... The axis is defined as the direction from that point towards the transverse North Pole. The axis is an auxiliary transverse parallel pointing eastward along that point, established on a transverse Mercator chart. The coordinate system is the transverse Mercator transverse coordinate system.

[0093] Understandably, the transverse Mercator coordinate system is referenced here. Figure 4 , Figure 4 This is a schematic diagram of the lateral geographic coordinate system provided in an embodiment of this application. The lateral Mercator lateral coordinate system is represented by lateral geographic projection onto a plane. Coordinate system correspondence Coordinate system.

[0094] Here, the lateral latitude of any point M on the ellipsoid is defined. Let be the angle between the normal to the ellipsoid at that point and the transverse equatorial plane. Let the coordinates of any point be (x, y, z), then the coordinates of the ellipsoidal normal vector at that point are: (CGCS2000 coordinate system). The lateral latitude of this point and the location of points at the same lateral latitude satisfy equation (1). Combining this with the equation of the Earth ellipsoid, we can obtain the equation of the lateral latitude: (1); (2).

[0095] Understandably, a horizontal parallel of latitude is an irregular curve; please refer to [reference needed]. Figure 5 , Figure 5 This is a schematic diagram of the transverse latitude line provided in an embodiment of this application. For ease of calculation, auxiliary transverse latitude lines are defined.

[0096] Auxiliary lateral latitude The formula is: (3).

[0097] The equation for the auxiliary transverse latitude is: (4).

[0098] It is understandable that the auxiliary transverse latitude is an equipotential ellipse, which is an ellipse formed by a plane parallel to the transverse equatorial plane cutting the Earth.

[0099] Ultimately, the relationship between lateral latitude and auxiliary lateral latitude is as follows: (5).

[0100] Naturally, please refer to Table 8, which shows the mapping relationship between a nautical chart coordinate system and a nautical chart projection scheme.

[0101] Table 8. Mapping Table of Nautical Chart Projection and Navigation Coordinate System:

[0102] Understandably, when choosing a polar spherical projection nautical chart as a high-latitude nautical chart, using the polar spherical grid coordinate system as the chart coordinate system directly supports the high-latitude navigation requirements based on the grid coordinate system. However, in special cases, when using a transverse Mercator projection nautical chart as a high-latitude nautical chart, using the transverse Mercator coordinate system as the chart coordinate system directly supports the high-latitude navigation requirements based on the transverse coordinate system.

[0103] Furthermore, a feasible implementation method is shown for step S30. Please refer to... Figure 6 , Figure 6 This is a schematic flowchart illustrating the process of determining the switching time according to an embodiment of this application. Step S30 includes: Step S31: Set the switching latitude and transition latitude range, wherein the transition latitude range is a continuous area extending to both sides of the preset latitude difference with the switching latitude as the center.

[0104] It's important to note that this step establishes the geographical framework for the switching decision. The switching latitude is a pre-defined key latitude threshold based on projection distortion theory, maritime safety rules, and historical experience. For example, the switching latitude for switching from Mercator projection to transverse Mercator projection might be set at latitude 83°. The transition latitude range is a continuous area extending from this switching latitude to both the higher and lower latitudes by a pre-defined latitude difference (e.g., 0.5°), i.e., the area from latitude 82.75° to 83.25° in this example. The technical function of this range is to provide a buffer zone for projection switching, avoiding display jumps or logical conflicts that might occur due to instantaneous switching along a single latitude line. The effect of this step is to define the geographical stage for switching events, transforming the timing judgment from monitoring a single point to monitoring an entire region, thus enhancing the system's robustness and fault tolerance.

[0105] Step S32: When the current latitude of the navigation vehicle is detected to enter the transition latitude range, obtain the heading of the navigation vehicle.

[0106] Understandably, this step is a conditional action that triggers data acquisition. The monitoring function is achieved by continuously providing geographic coordinates from the ship's onboard Global Navigation Satellite System (GNSS) receiver. When the system determines, through comparison, that the current latitude value has entered a preset transition latitude range, it triggers the subsequent judgment process. Obtaining the heading of the navigation vehicle refers to reading the ship's current heading from the gyrocompass or GNSS heading measurement unit, i.e., the angle of its direction of motion relative to true north. The benefit of this step is that it links the triggering of the switching judgment to a specific geographic event, namely entering the transition zone, and collects the key dynamic parameter required for the judgment—heading—providing a basis for subsequent analysis of the ship's intentions.

[0107] Specifically, step S32 involves obtaining the first entry heading of the navigation vehicle when the current latitude of the navigation vehicle first enters the transition latitude range.

[0108] Understandably, the first part defines the precise triggering time for data acquisition, and its key technology lies in the identification and judgment of the first entry into this state. This function relies on a simple state marking mechanism. The system needs to maintain a variable recording the state of the navigation vehicle relative to the transition latitude interval. When the shipborne GNSS positioning module continuously provides latitude and longitude data, the system compares the current latitude with the upper and lower limits of the transition interval in real time. Only when the previous state was outside the interval and the current latitude value meets the entry conditions is it determined to be the first entry, and subsequent operations are triggered, while the state mark is updated to be inside the interval. The effect of this design is that it ensures that critical heading data is collected only once at the moment of entry during the entire transit process, avoiding multiple, repetitive, or contradictory heading sampling caused by the ship maneuvering or wandering within the interval, providing a clear and unique initial direction reference for subsequent judgments.

[0109] Understandably, the latter part refers to the key navigation parameters collected at the specific triggering moment mentioned above. The first entry heading specifically refers to the ship's heading at the moment the vessel first crosses the boundary of the transition latitude interval. This data is provided by the real-time output of the gyrocompass at the moment of triggering and is immediately captured by the system and stored as a fixed value for subsequent logical judgment. The technical significance of this first entry heading is that it most directly reflects the initial intention and movement trend of the vessel when entering the transition buffer zone. Compared with the continuously changing real-time heading, this instantaneous heading value serves as a stable judgment benchmark, enabling the system to consistently assess whether the ship intends to penetrate deeper into the high-latitude region (heading towards the inside of the interval) or may briefly cross or is about to turn back (heading towards the outside of the interval).

[0110] Understandably, by locking in an initial state parameter with clear physical meaning, the entire switching timing judgment logic has a traceable starting point and a consistent judgment basis, which enhances the certainty and reliability of system decision-making and prevents false triggering caused by short-term course fluctuations.

[0111] Step S33: Based on the relative positional relationship between the heading of the navigation vehicle and the boundary latitude of the transition latitude interval, determine whether the preset switching trigger condition is met.

[0112] Understandably, this step constitutes the core intelligent judgment logic, and its technical essence is a heading-position relationship analysis algorithm. The relative position relationship refers to the angle between the ship's heading and the normal direction of the transition zone boundary. A feasible specific judgment logic is: when a ship enters the transition zone from the lower latitude side, and its real-time heading continuously points towards the higher latitude side, and it is predicted that it will cross the central switching latitude line in a short time, then the switching condition is met. Conversely, if the ship's heading points towards the lower latitude side, indicating that it may be leaving the higher latitude region, then the switching is not triggered. This judgment can be implemented by a state machine logic or prediction algorithm running in a microprocessor.

[0113] Specifically, step S33 is as follows: if the vehicle enters from the low latitude side outside the transition latitude interval and the first entry heading points to the latitude switch, then it is determined that the switching opportunity from the original nautical chart coordinate system to the target nautical chart coordinate system has been reached at the current position; if the vehicle exits from the high latitude side within the transition latitude interval, then it is determined that the switching opportunity from the target nautical chart coordinate system to the original nautical chart coordinate system has been reached when the vehicle exits the transition latitude interval.

[0114] Specifically, when the navigation system includes electronic nautical charts (or a charting system), the switching of the high-latitude coordinate system is determined by the high-latitude nautical chart switching. When the system uses Mercator projection charts, the navigation system output adopts the CGCS2000 coordinate system; when the system uses high-latitude projection charts, the navigation equipment output uniformly adopts the high-latitude coordinate system. The internal coordinate system switching of the navigation equipment is selected based on the error characteristics of each device, the speed of the carrier, and the navigation mission.

[0115] Specifically, when a vehicle travels from low to high latitudes, if the travel area crosses the right endpoint of a transition latitude interval, a switch to the high-latitude coordinate system should be performed at the switching latitude. If the vehicle travels within the transition latitude interval and crosses the switching latitude, it should switch to the high-latitude coordinate system. If it crosses the left endpoint of the transition latitude interval again, it should switch back to the conventional coordinate system. Similarly, when traveling from high latitudes to low to medium latitudes, if the vehicle crosses the left endpoint of a transition latitude interval, it should switch back to the conventional coordinate system at the switching latitude. Otherwise, the high-latitude coordinate system should be maintained.

[0116] Understandably, the technical effect of this step is to synchronize the triggering of the projection switching with the ship's actual navigation intention and motion state, ensuring that the switching action occurs while the ship is steadily sailing to a higher latitude region. This avoids unnecessary and potentially confusing repeated switching when the ship is lingering, turning around, or performing complex maneuvers in the transition zone, thus achieving a safe, natural, and intuitive automated projection conversion.

[0117] In a feasible implementation, step S40 specifically involves: determining the first coordinate system parameters corresponding to the target nautical chart projection and the second coordinate system parameters corresponding to the original nautical chart projection; obtaining the first coordinate data of the navigation vehicle in the original nautical chart coordinate system corresponding to the switching timing; calling the coordinate transformation formula corresponding to the types of the target nautical chart projection and the original nautical chart projection, and combining the first coordinate system parameters and the second coordinate system parameters to convert the first coordinate data into the second coordinate data in the target nautical chart coordinate system.

[0118] It should be noted that, with the pole as the origin, the polar sphere projection coordinates are denoted as... Mercator projection coordinates are The transformation formula between the polar spherical projection coordinate system and the Mercator projection coordinate system is as follows: (6).

[0119] In the formula, c is a coefficient related to the reference latitude; This is the length ratio coefficient, used to adjust the degree of deformation of the region's length. In standard usage, its value is set to 1.

[0120] Similarly, the transformation formula between the Mercator projection coordinate system and the polar spherical coordinate system is as follows: (7).

[0121] Let the pole be the origin of the coordinate system, and let R be the radius of the sphere. The reference polar moment, polar spherical coordinates The projection formula is as follows: (8).

[0122] In the formula, This is the length ratio coefficient, used to adjust the degree of deformation of the region's length. In standard usage, its value is set to 1.

[0123] For ease of derivation, let: (9). At this point, equation (8) can be expressed as: (10).

[0124] It should be noted that the Mercator projection coordinates are... The formula for the positive Mercator projection is as follows: (11).

[0125] In the formula, c is a coefficient related to the reference latitude. Substituting into equation (10), the conversion formula between the Mercator projection coordinate system and the polar spherical projection coordinate system is as follows: (12).

[0126] Similarly, the transformation formula between the polar spherical projection coordinate system and the Mercator projection coordinate system is as follows: (13).

[0127] It is understandable that if the original projection is a Mercator projection, then the first coordinate data is the Mercator projection coordinate as defined in the text. If the original projection is a polar projection, then the first coordinate data is the polar projection coordinate. or its equivalent polar spherical coordinates At the moment the switching is triggered, the navigation system obtains precisely this set of coordinate values ​​from the positioning sensors and the current projection calculation model, which serves as the input for the transformation.

[0128] Similarly, the first coordinate system parameters and the second coordinate system parameters are the target nautical chart projection coordinate system parameters and the original nautical chart projection coordinate system parameters, respectively. The transformed second coordinate data can be obtained by calling formulas (12) and (13).

[0129] It should be noted that after step S40, the method further includes: providing the second coordinate data to the navigation system so that the navigation system can display and plot navigation elements on the nautical chart using the target nautical chart projection based on the second coordinate data.

[0130] Understandably, upon receiving new coordinate data, the navigation system's display and control module will immediately drive two core sub-processes: first, it will retrieve the electronic chart (ENC) data matching the target nautical chart projection and render the chart data onto the screen according to the mathematical rules of the target projection (i.e., the corresponding projection formula described in the document); second, it will use the received second coordinate data, already in the target coordinate system, as the reference for drawing the ship's position symbol. Simultaneously, the system must batch convert the coordinates of all other dynamic elements, such as AIS targets of other ships, route plans, waypoints, and radar overlay information, to the target coordinate system using the same conversion logic as in step S40, and plot them together on the new projected nautical chart background.

[0131] Understandably, it achieves a seamless transition from data calculation to visual perception. By automatically and in real-time providing the converted coordinate data to the navigation display system, it ensures that the relative positions of all key information—including the ship's own position, planned route, surrounding obstructions, and other vessels—remain continuous, accurate, and intuitive on the screen before and after the projection switch. This eliminates the need for the driver to manually switch charts, reposition, or perform mental calculations, significantly reducing workload and the risk of misjudgment. It makes complex navigation in high-latitude regions as intuitive and reliable as in mid- and low-latitude regions, fundamentally ensuring navigational safety.

[0132] Based on the above implementation methods, this application firstly standardizes the selection of nautical chart projections; by analyzing the characteristics of different nautical chart projections, it transforms the original experience-based selection process into a data-driven objective decision-making process. Secondly, it achieves deep coupling between nautical charts and navigation systems; selecting a nautical chart projection requires matching the corresponding nautical chart coordinate system with the navigation system, improving the adaptability of nautical charts within the navigation system and reducing coordinate system transformations within the system. Finally, it ensures the reliability of the switching process: by establishing transition latitude intervals, the switching between mid-to-low latitude and high latitude nautical chart projections and the transformation of nautical chart coordinate systems are no longer abrupt jumps, but rather a controllable gradual change, improving the reliability of the navigation system.

[0133] In addition, a second aspect of this application provides an embodiment of a device for selecting and switching nautical chart projections. Please refer to... Figure 7 , Figure 7 This is a schematic diagram of the high-latitude nautical chart projection selection and switching device provided in an embodiment of this application. The device includes: The projection determination module is used to determine the target nautical chart projection from a variety of predefined nautical chart projections based on the geographical latitude of the target navigation area.

[0134] The coordinate system determination module is used to determine the nautical chart coordinate system that matches the target nautical chart projection, based on the type of the target nautical chart projection.

[0135] The switching timing judgment module is used to determine whether the timing for switching the nautical chart coordinate system has been reached when the navigation vehicle enters the preset high-latitude switching area during navigation, based on the real-time navigation information of the navigation vehicle.

[0136] The coordinate transformation module is used to transform between the target nautical chart coordinate system and the original nautical chart coordinate system when it is determined that the time for switching the nautical chart coordinate system has arrived, based on the preset coordinate system transformation relationship.

[0137] It is understood that the detailed functional implementation of each of the above units / modules can be found in the description in the foregoing method embodiments, and will not be repeated here.

[0138] Compared with existing technologies, the high-latitude nautical chart projection selection and switching device provided in this application transforms the logical process into a structured and automated structure through the coordinated operation of the above four modules. It encapsulates the complex projection selection, coordinate system matching, and dynamic switching judgment into independent processing units, enabling the projection management of high-latitude navigation to be integrated into the ship navigation system and achieve fully automated processing without human intervention.

[0139] Compared with existing technologies, the core beneficial effects of this device are consistent with the implementation of its method, namely, systematically solving the three major problems of difficult projection selection, mismatch between projection and coordinate system, and discontinuous switching process in high-latitude navigation. Through automated decision-making and seamless conversion, it significantly improves the safety and navigation efficiency of high-latitude navigation.

[0140] Based on the methods in the above embodiments, please refer to Figure 8 , Figure 8 This is a schematic diagram of the structure of the nautical chart processing device provided in this application embodiment. This application embodiment provides a nautical chart processing device, which may include: a processor, a communications interface, a memory, and a communication bus, wherein the processor, communications interface, and memory communicate with each other through the communication bus. The processor can call logical instructions in the memory to execute the methods described in the above embodiments.

[0141] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application.

[0142] Based on the methods in the above embodiments, this application provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0143] Based on the methods in the above embodiments, this application provides a computer program product that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0144] It is understood that the processor in the embodiments of this application can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0145] The method steps in this application embodiment can be implemented in hardware or by a processor executing software instructions. The software instructions can consist of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can reside in an ASIC.

[0146] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0147] It is understood that the various numerical designations used in the embodiments of this application are merely for the convenience of description and are not intended to limit the scope of the embodiments of this application.

[0148] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for selecting and switching high-latitude nautical chart projections, characterized in that, include: Step S10: Determine the target nautical chart projection from a variety of predefined nautical chart projections based on the geographical latitude of the target navigation area; Step S20: Determine the nautical chart coordinate system that matches the target nautical chart projection according to the type of the target nautical chart projection; Step S30: When the navigation vehicle enters a preset high-latitude switching area during navigation, based on the real-time navigation information of the navigation vehicle, determine whether the timing for switching the nautical chart coordinate system has been reached. This includes: setting a switching latitude and a transition latitude interval, wherein the transition latitude interval is a continuous area extending to both sides of a preset latitude difference with the switching latitude as the center; when the current position latitude of the navigation vehicle is detected to enter the transition latitude interval for the first time, obtain the first entry heading of the navigation vehicle; if the navigation vehicle enters from the low-latitude side outside the transition latitude interval, and the first entry heading points to the switching latitude, then it is determined that the timing for switching from the original nautical chart coordinate system to the target nautical chart coordinate system has been reached at the current position; if the navigation vehicle exits from the high-latitude side within the transition latitude interval, then it is determined that the timing for switching from the target nautical chart coordinate system to the original nautical chart coordinate system has been reached when the navigation vehicle exits the transition latitude interval. Step S40: When it is determined that the timing for switching the nautical chart coordinate system has arrived, a conversion is performed between the target nautical chart coordinate system and the original nautical chart coordinate system based on a preset coordinate system conversion relationship.

2. The method for selecting and switching high-latitude nautical chart projections as described in claim 1, characterized in that, Step S10 includes: Obtain at least one geographic coordinate point within the target navigation area; Based on the latitude of the geographic coordinates, the target latitude interval to which the target navigation area belongs is determined from a first latitude interval, a second latitude interval, or a third latitude interval, wherein the upper limit latitude of the first latitude interval is lower than the lower limit latitude of the second latitude interval, and the upper limit latitude of the second latitude interval is lower than the lower limit latitude of the third latitude interval. The target nautical chart projection is determined based on the preset correspondence between the target latitude range and various nautical chart projections.

3. The method for selecting and switching high-latitude nautical chart projections as described in claim 2, characterized in that, Before step S10, the following are also included: Establish a multi-dimensional characteristic evaluation model for various nautical chart projections. The multi-dimensional characteristic evaluation model includes at least evaluation dimensions for angular distortion, length distortion, the degree of approximation between meridians and straight lines, and the degree of approximation between great circle routes and straight lines. Based on the aforementioned multi-dimensional characteristic evaluation model, the applicability of different nautical chart projections in different latitude ranges is evaluated. Based on the evaluation results, a preset correspondence is established between the latitude interval and the nautical chart projection.

4. The method for selecting and switching high-latitude nautical chart projections as described in claim 1, characterized in that, Step S40 includes: Determine the first coordinate system parameters corresponding to the target nautical chart projection, and the second coordinate system parameters corresponding to the original nautical chart projection; Obtain the first coordinate data of the navigation vehicle in the original nautical chart coordinate system corresponding to the switching timing; The coordinate transformation formula corresponding to the type of the target nautical chart projection and the original nautical chart projection is invoked, and the first coordinate data is converted into second coordinate data in the target nautical chart coordinate system by combining the first coordinate system parameters and the second coordinate system parameters.

5. The method for selecting and switching high-latitude nautical chart projections as described in claim 4, characterized in that, After step S40, the following is also included: The second coordinate data is provided to the navigation system so that the navigation system can display and plot navigation elements on a nautical chart projected with the target nautical chart based on the second coordinate data.

6. A device for selecting and switching nautical chart projections, characterized in that, The device includes: The projection determination module is used to determine the target nautical chart projection from a variety of predefined nautical chart projections based on the geographical latitude of the target navigation area. The coordinate system determination module is used to determine a nautical chart coordinate system that matches the target nautical chart projection based on the type of the target nautical chart projection. The switching timing determination module is used to determine whether a switching timing for the nautical chart coordinate system has been reached when a navigation vehicle enters a preset high-latitude switching area during navigation, based on the real-time navigation information of the navigation vehicle. This includes: setting a switching latitude and a transition latitude interval, wherein the transition latitude interval is a continuous area extending to both sides of a preset latitude difference centered on the switching latitude; when the current position latitude of the navigation vehicle is detected to enter the transition latitude interval for the first time, obtaining the first entry heading of the navigation vehicle; if the navigation vehicle enters from a low-latitude side outside the transition latitude interval, and the first entry heading points to the switching latitude, then it is determined that a switching timing from the original nautical chart coordinate system to the target nautical chart coordinate system has been reached at the current position; if the navigation vehicle exits from the high-latitude side within the transition latitude interval, then it is determined that a switching timing from the target nautical chart coordinate system to the original nautical chart coordinate system has been reached when the navigation vehicle exits the transition latitude interval. The coordinate transformation module is used to transform between the target nautical chart coordinate system and the original nautical chart coordinate system based on a preset coordinate system transformation relationship when it is determined that the timing for switching the nautical chart coordinate system has arrived.

7. A nautical chart processing device, characterized in that, include: Memory, one or more processors; The memory is coupled to the one or more processors, and the memory is used to store computer program code, the computer program code including computer instructions; The one or more processors invoke the computer instructions to cause the nautical chart processing device to perform the high-latitude nautical chart projection selection and switching method as described in any one of claims 1 to 5.

8. A storage medium comprising instructions, characterized in that, The storage medium is a computer-readable storage medium; When the instruction is executed on the nautical chart processing device, the nautical chart processing device performs the high-latitude nautical chart projection selection and switching method as described in any one of claims 1 to 5.

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