Self-adaptive road network generation method for propaganda schematic art map

Abstract

According to the self-adaptive road network generation method for the propaganda schematic art map, the node transformation method is applied, the drawing rule of the schematic map is fused into the algorithm, the schematic map automatic generation algorithm is developed, and automatic generation of the schematic map is achieved. And designing a drawing rule of a schematic map, particularly improving the drawing rule in the aspects of a topology consistency rule, a length relativity rule and the like, and determining the drawing rule which needs to be followed by an algorithm. And designing an automatic generation model of the schematic map, and performing schematic expression on a drawing rule in the model. According to the designed model, schematic map automatic generation algorithms including a grid segmentation method, a road network hub point extraction method, a road network feature simplification method and a road network deformation method are researched and developed. The algorithm has high applicability, the road network generation algorithm is low in complexity and high in speed, and map generation in a complex scene functionally meets schematic diagram making and is artistic.

Description

Technical Field

[0001] The present application relates to a method for generating a schematic map road network, and in particular to a method for generating an adaptive road network for a promotional schematic artistic map, belonging to the technical field of artistic map generation methods. Background Art

[0002] GIS, a discipline born from the integration of cartography and geography, has significantly advanced cartography and cartography science in a computer-based environment. Map readers can create maps based on their specific needs, while map makers can also produce market-oriented maps based on customer requirements. Map design strives for more effective expression and enriches the diversity of maps. Maps can be expressed in many forms, such as wind direction and flow. However, public transportation maps are the most commonly used form of map expression. Unlike other map forms, they are relatively easy to recognize. Public transportation maps, primarily through a specific map language and practical rules, abstractly represent information such as traffic types and route directions in complex urban transportation networks. From a navigation perspective, they play a crucial role and have become a common tool for spatial information representation.

[0003] As urban infrastructure continues to improve, transportation networks have become more complex and diverse. Traditional transportation network maps contain too much information that people rarely need when traveling. The human brain needs to filter out this redundant information, making map reading more difficult. Therefore, how to express the information people need in a simple form on maps has become a research hotspot. This, combined with spatial cognitive psychology, has led to the concept of schematic maps.

[0004] Schematic maps highly summarize the important parts of a map, providing users with the key information they need through graphical representation. This information can be transmitted to the reader's mind quickly and effectively, helping to form a mental image. Schematic maps differ from traditional maps in that they condense the content of traditional maps, avoiding the excessive and redundant details often found on traditional maps. Schematic maps can simply depict the distribution of relevant transportation routes in a city, the connectivity between stations and routes, and so on.

[0005] Currently, there's no consensus on the design rules for schematic map diagrams. This is because different approaches often lead to different design rules to meet the design requirements of automated algorithms. Furthermore, within network arcs, the relative length relationships and the relative position relationships of nodes must be maintained, but these relationships are incorporated into the standard for schematic production. Cartographers, based on their previous experience, believe that the relative rule is a crucial factor in the recognition of schematic maps. However, there's no concrete, objective basis to support the specific implementation requirements of this rule, nor has it been verified.

[0006] The problems that need to be solved by the existing complex image key area detection method and the key technical difficulties of this application include:

[0007] (1) The design rules and corresponding algorithms used in the existing technology for automatic generation of map schematics mainly have the following problems: First, the automatic generation algorithm only optimizes the original road network under vector conditions, but image optimization and image deformation in the field of image processing have developed rapidly, and current algorithms rarely draw on image algorithms for related research. Second, the design rules of schematic maps have not yet been unified. The current automatic generation of schematic map algorithms involve various design rules. In addition to the network topology relationship consistency rule, different algorithms focus on different directions and lack a universal design rule. Third, from a spatial perspective, the readability of current schematic maps has not yet been improved. Only the position of points in the local area is optimized without considering the overall spatial distribution of the map. When manually drawing schematic maps, in addition to considering the consistency of the relative position relationship of the map network, the overall aesthetics and readability of the map must also be optimized to meet the needs of merchants. Fourth, there is currently little objective research on relative rules and how to apply them to schematic maps. Fifth, there is a lack of objective research on design rules. The design rules used in current schematic maps are only those specified by mapping professionals, rather than those generally recognized by the design industry.

[0008] (2) At present, schematic maps are all drawn manually by professional cartographers. The results of their mapping are subject to many constraints, and the differences in mapping experience lead to great differences in the effects of schematic maps. Since schematic maps are more integrated with artistic elements, they must be as beautiful as possible while ensuring accuracy. Therefore, in the automatic generation of map schematics, it is difficult to design artistic elements as mapping rules and integrate them into the algorithm. The time complexity of the current automatic generation algorithm of schematic diagrams is high, and the algorithm performance is imperfect. There is a lack of methods for constructing and optimizing site spatial indexes, a lack of applying algorithmic processing ideas in images to the automatic generation algorithm of schematic maps, and a lack of schematic map generation algorithms based on grid transformation. The quality and efficiency of the generation of publicity schematic maps are relatively low, and the adaptability and artistry are poor.

[0009] (3) Currently, schematic maps are still drawn manually by cartographers. During the design and drawing process, cartographers spend a lot of time to schematically express the schematic planning of routes. If the routes are updated, the synchronous update of the schematic map is also cumbersome. Unlike traditional maps, schematic maps follow more cartographic constraints during the production process, such as distance rules and direction rules. At this stage, there is no unified understanding of the design rules for the schematicization of map diagrams. For the rules that have been designed, it is very difficult to produce more complex schematic maps of traffic networks according to them if the design relies solely on manual work. Semi-automatic or even automated algorithms are urgently needed to draw and produce schematic maps. Summary of the Invention

[0010] This application uses a grid segmentation method, node transformation and interpolation methods to effectively arrange the nodes according to the design rules of the schematic map, and finally generates the final schematic result; for the selection of key sites, a fast method is adopted to extract the nodes with transfer sites as the target, and the extracted transfer sites are used as segmentation sites, and the features of other sites between the transfer sites are extracted to maximize the original characteristics of the line; the points are translated and interpolated in the buffer grid, so that the lines connected by the points in each buffer grid meet the direction design rules of the schematic map; in line simplification, the efficiency of line simplification is improved by optimizing the iterative splitting and merging algorithm; in node transformation, the transformation state of the points is judged, and the interpolated point position and relative topological relationship are calculated. Experiments are conducted using Beijing's urban rail transit data. It can be seen from the experimental results that this application can handle node transformation in complex road networks very well, and can generate road networks efficiently and accurately, with fast speed and the generated road networks are concise and clear.

[0011] To achieve the above technical effects, the technical solutions adopted in this application are as follows:

[0012] The method for generating an adaptive road network for a schematic art map is based on grid segmentation. Node transformation and interpolation are used to arrange nodes according to the design rules of the schematic map, and the final schematic result is generated. For the selection of key stations, a fast method is adopted. Nodes are extracted with transfer stations as the target, and the extracted transfer stations are used as segmentation stations. Feature extraction is performed on other stations between transfer stations to maximize the original characteristics of the route. Finally, the points are translated and interpolated within the buffer grid, so that the lines connected by the points in each buffer grid meet the directional design rules of the schematic map. In line simplification, the efficiency of line simplification is improved by optimizing the iterative splitting and merging algorithm. In node transformation, the transformation status of the points is judged, and the interpolated point positions and relative topological relationships are calculated.

[0013] First, the map is divided and segmented using a grid segmentation method based on regular grids;

[0014] The second is the selection rule of the road network hub: the transfer stations are determined by counting the number of various points, and the transfer stations are used as hubs to maintain the skeleton of the network;

[0015] The third is adaptive simplification of road network features: an optimized non-recursive iterative splitting and combining algorithm is used to simplify lines. The recursive iterative splitting and combining algorithm is converted into a non-recursive iterative splitting and combining algorithm through a stack.

[0016] Fourth, the road network is artistically deformed point by point: the transformation area is selected through the orientation neighborhood index method, the map is converted into a regular grid map, the selection space of the transformation area is conveniently selected through neighborhood selection, and the construction is assisted by the buffer zone, and the buffer zone is constructed to reorganize the data structure; a road network transformation model is established to analyze the three situations in the road network transformation, and solutions are established for the three situations of direct transformation of points, transformation of points taking into account the front and back points, and interpolation of point transformation; finally, based on the three transformations, a transformation equation is established, and the two parameters of position information and topological transformation information are input. Then, through proportional transformation, each point in the area is translated to the corresponding proportion to realize the road network transformation.

[0017] Preferably, a grid schematic model is generated: rule-guided grid segmentation is performed, by constructing M×N grids, all sites on the map are stored in grids, and the retrieval and grid transformation calculations are facilitated;

[0018] 1) Constructing an adaptive grid: The line name to which the station belongs is used as the station's attribute number, and the rectangular boundary of the map formed by the station is calculated, that is, the maximum and minimum values of the horizontal and vertical coordinates of the station, and the number of stations and nodes is counted to calculate the size of the grid;

[0019] Calculate the row and column number of each point in the grid and construct the grid index number

[0020] 2) Minimize the grid size: Based on the infinite approximation model, a method for minimizing the grid size is established. On the basis of constructing an adaptive grid, the size of the grid is infinitely reduced, and finally the grid is replaced by points for calculation;

[0021] The minimization method is used to replace the nodes with grids. The original map is drawn based on the real road network. The grid is set to 1 meter. For the thousand-fold reduction change, the grid is replaced by nodes for calculation.

[0022] Preferably, the hub point selection is based on the road network tortuosity fluctuation model: the hub point is selected by the road network tortuosity fluctuation to better maintain the changes in the road graph. Through the tortuosity calculation, the areas with higher and lower road change significance are found. For the road sections with higher significance, the significance is maintained, and for the road sections with lower significance, the significance is not maintained. The curvature of each node is first calculated, and the average value of the curvature of each node ranges from 0 to 1. If it is closer to 1, it indicates that the tortuosity change of this section of road is greater and the significance is higher; if it is closer to 0, it indicates that the tortuosity change of this section of road is smaller, and the closer it is to a straight line, the lower the significance.

[0023] Preferably, the hub point selection based on the transfer station is as follows: the transfer station is used as the hub point, and the original road conditions of the main and secondary subway line maps are maintained;

[0024] For the selection of transfer stations, one method is to judge by the number of grid nodes, and the other is to judge by the degree of the nodes by constructing a network graph;

[0025] (1) Judging by the number of grid points: The map points are divided into grids based on regular grids. In the divided grids, for each node of each line, there is at most one point in the grid where it is located, that is, the point itself. If there are two or more points in the grid, it indicates that the grid is a transfer station grid, and the transfer station can be found. Each point has a route number attribute. The transfer station grid will record which two or several lines the transfer point belongs to;

[0026] Select transfer stations based on the number of transfer station nodes and mark the transfer station grid;

[0027] (2) Judgment by constructing a network graph: Introducing graph theory from discrete mathematics into geographic networks, only three concepts in graph theory are considered, namely, the graph G consisting of a set of nodes and a set of edges, and the number of edges associated with each node, which is the degree of the node;

[0028] For a transfer station, the node degree of an ordinary station should be less than or equal to 2, and the node degree of a transfer station should be greater than or equal to 3. The transfer station is detected by this method.

[0029] Preferably, two hub point selection methods are integrated: hub points are selected based on the change in the tortuosity of the road network, preserving the shape characteristics of the road network itself to the greatest extent;

[0030] Based on the hub point selection of transfer stations, the route is divided. For each divided road, the hub point is selected again, which will better maintain the original characteristics of the road network.

[0031] The two hub point selection methods are combined. After extracting the transfer stations, the nodes and stations between the transfer stations are simplified and extracted.

[0032] Preferably, the road network characteristics are adaptively simplified: the first and last points of each curve are simulated and connected, and the parametric equation of the connection line is obtained. Then, the distances from all nodes to the straight line are obtained, and the maximum distance between them is obtained and compared with the set critical value limit.

[0033] Preferably, a non-recursive optimization method is adopted: to ensure that the extreme points obtained in the middle are not discarded during the processing, the curve is divided into two parts at the extreme point of the bend, and it is processed into two sections. For the extreme point of the bend, the angle between the middle point and the two adjacent vertices is measured. Combined with the stack data structure, a segmentation method is adopted. It starts from one end of the curve, first uses the first and last points as identification points, and uses them as the working section. Then, it is determined whether the distance between the farthest point calculated in the middle is greater than the critical value. In this way, the comprehensive simplification of line elements is completed. The specific steps of the improvement are as follows:

[0034] Step 1: Find the point with the largest curvature in the curve, divide the curve into two parts based on this point, and create a point list for each part. Then process the two curves separately.

[0035] Step 2: For the first curve segment, there is a sequence of vector calculated points, forming a line segment, generating a stack, and pushing the points into the stack;

[0036] Step 3: Find the farthest node between the line segments, denoted as C, and the distance is Dist;

[0037] Step 4: Determine whether the distance from the node to the first curve segment is less than a given critical value. If not, add point C to the feature sequence, push the node into the stack, connect the two points with a line segment, and return to step 3. If yes, execute step 5.

[0038] Step 5: Determine whether the node is equal to the top element of the stack. If it is not the top element of the stack, connect the two points and return to step 3. If so, execute step 6.

[0039] Step 6: Determine whether the distance from the node to the second curve segment is greater than a given critical value. If not, set the node to represent the next point on the stack, connect the line segments, pop the top element of the stack, and then return to step 3.

[0040] Step 7: When the stack is empty, the first segment of the curve is finished, and the second segment of the curve is processed in the same way, and steps 1 to 7 are repeated.

[0041] Preferably, the road network is artistically deformed point by point: a point-by-point transformation method of the road network is established, and only one transformation is performed on all points without subsequent position changes, that is, the points are transformed to the final generated schematic position in one step;

[0042] When performing point-by-point transformations, consider the following two aspects:

[0043] (1) Transformation area: For the transformed points, other points within a certain buffer range are considered to ensure that their relative positions do not change. Within a certain buffer zone, the transformation methods and transformation equations of all points are consistent, and the point distribution is kept as close to that on the original map as possible;

[0044] (2) Transformation model: For points that have not been transformed, certain point transformations are performed to generate points that meet the direction requirements. For points that have been transformed, the position of the point is guaranteed to remain unchanged, while other points are transformed. If two points in the area have been transformed and the line segment connecting the two points cannot meet the direction requirements of the schematic subway map, a point needs to be interpolated between the two points to meet the eight-direction rule between the points.

[0045] Preferably, the transformation local area is selected: according to the node currently requiring transformation, all nodes within a certain range around it are transformed simultaneously. The transformation area selection method in the network construction mode includes:

[0046] 1) Azimuth neighborhood indexing method:

[0047] In image smoothing, for the pixel value of the current point after smoothing calculation, the pixel values of the eight surrounding neighborhoods (i.e., the point's upper, lower, left, right, upper left, lower left, upper right, and lower right) are used to calculate the average value as the output pixel value of the point, and the pixel values of the four points in its four neighborhoods (i.e., the point's upper, lower, left, and right) are used to calculate the average value as the output pixel value of the point; all points in the neighborhood are selected, and these nodes are transformed to maintain the consistency of their topological relationships;

[0048] 2) Buffer neighborhood index with a certain radius:

[0049] The buffer zone is a polygon of a certain width that is automatically established around each node based on the situation analysis required. The data structure of the point is changed to facilitate the neighborhood search and speed up the buffer zone retrieval.

[0050] Preferably, the artistic model is transformed: the transformation of the point position is reflected in the translation transformation. The translation transformation is to transform the positions of all the nodes of the graph in the same way of movement, which is divided into the following three cases:

[0051] (1) The point to be changed is the node sequence number in the road: the point is the point before the second to last point in the entire point sequence. If it is lower than this, only the current point is changed, and the next two points are not considered;

[0052] (2) The number of road nodes to be transformed is greater than or equal to three, and the transformation point is the second-to-last node in the entire road. The previous point is a transformed point, and the next point is the end point of the feature. After the transformation of this point, the angles formed by the straight lines between it and the two previous and next points should all satisfy the eight-direction rule;

[0053] (3) When the total number of road nodes to be transformed is two, the first and last points are both feature points and cannot be transformed. In this case, a point needs to be interpolated to satisfy the eight-direction rule.

[0054] There are three situations for point position transformation mentioned above. The design of the transformation model is divided into three parts: the first is the direct transformation of the point to be transformed, the second is the point position transformation taking into account the direction of the previous and next points, and the third is the interpolation transformation of the point position.

[0055] Direct transformation of the points to be transformed: Using the rule of constructing an eight-direction map diagram, the points to be transformed are transformed horizontally, vertically, and at 45° angles. The nodes outside the line segment are the nodes to be transformed, and the nodes inside the line segment are the transformed nodes. First, the angle between the line segment and the horizontal direction is calculated, the angle is judged, and the point is projected to the direction closest to it. When the angle between the line segment and the horizontal direction is less than 22.5°, it is concluded that the projection to the X-axis is the most appropriate. The point to be transformed is projected onto the X-axis to complete the point transformation of the single point.

[0056] At the same time, if the point position is transformed to the 45° direction, there are three processing methods:

[0057] (1) The x-coordinate of the node remains unchanged, and the y-coordinate is transformed and translated to the 45° direction;

[0058] (2) Keep the y coordinate of the point unchanged and transform the x coordinate to move it to the 45° direction;

[0059] (3) Project the point to the 45° direction;

[0060] Based on the need to maintain the consistency of line segment proportions between points, the points are projected to the 45° direction to better maintain the line segment proportion consistency rule.

[0061] Compared with the existing technology, the innovation and advantages of this application are:

[0062] (1) This application uses a grid segmentation method, node transformation and interpolation methods to effectively arrange the nodes according to the design rules of the schematic map, and finally generates the final schematic result; for the selection of key sites, a fast method is adopted to extract the nodes with the transfer site as the target, and the extracted transfer site is used as the segmentation site, and the features of other sites between the transfer sites are extracted to maximize the original characteristics of the line; the points are translated and interpolated in the buffer grid, so that the lines connected by the points in each buffer grid meet the direction design rules of the schematic map; in line simplification, this application improves the efficiency of line simplification by optimizing the iterative splitting and merging algorithm; in the node transformation, the transformation state of the point is judged, and the interpolated point position and relative topological relationship are calculated, so the amount of calculation in this transformation is large, but since all the nodes have been indexed in the previous grid construction, it is also very helpful to speed up the calculation of this part. In order to verify the universality of the algorithm of this application in complex situations, experiments were conducted using urban rail transit data from Beijing. The experimental results show that this application can handle node transformations in complex road networks very well, and can generate road networks efficiently and accurately, with fast speed and concise and clear generated road networks.

[0063] (2) This application firstly adopts a grid segmentation method based on a regular grid to segment the map; secondly, it establishes a rule for selecting hub points of the road network, and adopts a method of judging transfer stations by calculating the number of various points, and taking transfer stations as hub points to maintain the skeleton type of the network. Thirdly, it adaptively simplifies road network features: adopts an optimized non-recursive iterative splitting and combining algorithm to simplify lines, and transforms the recursive iterative splitting and combining algorithm into a non-recursive iterative splitting and combining algorithm through a stack method, which greatly improves efficiency. Fourthly, it artistically deforms the road network point by point: selects the transformation area through the azimuth neighborhood index method, converts the map into a regular grid map, and facilitates the selection space of the transformation area through neighborhood selection, and assists in construction through a buffer, and constructs a buffer to reorganize the data structure; based on the road network transformation model, it analyzes three situations in the road network transformation, and respectively establishes the direct transformation of the point position, the transformation of the point position taking into account the previous and next points, and the solution of the interpolated point position transformation; finally, based on the three transformations, it establishes a transformation equation to realize the road network transformation. Beijing's subway line data was used. Experimental results show that the algorithm in this application can better ensure that the line structure features are similar to the original map, especially better ensure that the relative positions between transfer stations remain unchanged, and better restore the actual situation of the subway line.

[0064] (3) This application applies the node transformation method, integrates the mapping rules of schematic maps into the algorithm, develops an automatic schematic generation algorithm, and realizes the automatic generation of schematic maps. Summarize the existing schematic map mapping rules, point out the existing problems, and then propose the solution of this application. Analyze and design the mapping rules of schematic maps, especially improve the main mapping rules in terms of topological consistency rules, length relativity rules, etc., and determine the mapping rules that the algorithm needs to follow. Design an automatic generation model for schematic maps, and express the mapping rules in the model in a schematic way. Based on the designed model, an automatic generation algorithm for schematic maps was developed, which includes a grid segmentation method, a hub point extraction method for the road network, a road network feature simplification method, and finally a road network deformation method. The algorithm of this application has strong applicability, the road network generation algorithm has low complexity and fast speed, and the map generation functionality in complex scenarios meets the requirements of schematic production and is artistic. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a schematic diagram of the transfer station extraction results.

[0066] Figure 2 It is a direct transformation diagram of the point to be transformed.

[0067] Figure 3 This is the original map of Beijing's subway rail transit lines.

[0068] Figure 4This is a schematic map of the Beijing subway generated for this application method. DETAILED DESCRIPTION

[0069] The following further describes the technical solution of the method for generating an adaptive road network for a promotional schematic art map provided by this application in conjunction with the accompanying drawings, so that those skilled in the art can better understand this application and implement it.

[0070] With the rapid development of cities, schematic maps play a vital role in promoting cities and helping people plan their daily routes. However, most current schematic maps are manually drawn by professional cartographers, resulting in numerous constraints and significant variations in the quality of schematic maps due to differences in cartographic experience. Because schematic maps often incorporate artistic elements, ensuring accuracy while maintaining aesthetics, it is difficult to incorporate these elements into the automatic generation of map diagrams as mapping rules. Current algorithms for automatic diagram generation suffer from high time complexity and imperfect performance.

[0071] The present application uses a grid-based segmentation method, node transformation and interpolation methods to effectively arrange nodes according to the design rules of the schematic map and finally generate a final schematic result. For the selection of key stations, a fast method is adopted to extract nodes with transfer stations as the target, and the extracted transfer stations are used as segmentation stations. Feature extraction is performed on other stations between transfer stations to maximize the original characteristics of the route. Finally, the points are translated and interpolated within the buffer grid so that the route connected by the points in each buffer grid meets the directional design rules of the schematic map. In the entire algorithm, the most time-consuming part is the route simplification and node transformation. In route simplification, the present application improves the efficiency of line simplification by optimizing the iterative splitting and combining algorithm. In the node transformation, the transformation status of the points is judged, and the interpolated point position and relative topological relationship are calculated. Therefore, the amount of calculation in this transformation is relatively large. However, since all nodes have been indexed in the previous grid construction, it is also very helpful to speed up the calculation of this part.

[0072] This application uses Beijing's subway line data. Experimental results show that the algorithm of this application can better ensure that the line structure characteristics are similar to the original map, especially better ensure that the relative positions between transfer stations remain unchanged, and better restore the actual situation of the subway line.

[0073] 1. Generate a schematic mesh model

[0074] Rule-guided grid segmentation: By constructing M×N grids, all sites on the map are stored in grids to facilitate retrieval and grid transformation calculations.

[0075] (1) Constructing an adaptive grid

[0076] The line name to which the station belongs is used as the station's attribute number, and the rectangular boundary of the map formed by the station is calculated, that is, the maximum and minimum values of the horizontal and vertical coordinates of the station, and the number of stations and nodes is counted to calculate the size of the grid;

[0077] Calculate the row and column number of each point in the grid and construct the grid index number

[0078] (2) Constructing the minimum grid size

[0079] Based on the infinite approximation model, a method for minimizing the grid size is established. On the basis of constructing an adaptive grid, the size of the grid is infinitely reduced, and finally the grid is replaced by points for calculation.

[0080] The minimization method is used to replace the nodes with grids. The original map is drawn based on the real road network. The grid is set to 1 meter. For the thousand-fold reduction change, the grid is replaced by nodes for calculation.

[0081] Advantages of constructing a regular grid: The method of constructing a regular grid is simple, because the length and width of the grid are fixed, the calculation is relatively simple, and the retrieval speed is fast. For the subsequent point offset and line deformation, the offset of the point in the regular grid can be calculated by the offset of the grid, which is more convenient and faster. In particular, by minimizing the size of the grid, the offset of the point can be directly converted into the offset of the grid for calculation, which further simplifies the complexity of the calculation.

[0082] 2. Extracting road network hubs

[0083] (1) Hub point selection based on the road network tortuosity fluctuation model

[0084] The hub points are selected based on the fluctuation of the road network tortuosity to better maintain the changes in the road graph. Through tortuosity calculation, areas with higher and lower road change significance are found. For road sections with higher significance, more attention is paid to maintaining significance. For road sections with lower significance, there is no need to maintain significance. First, the curvature of each node is calculated. The average value of the curvature of each node ranges from 0 to 1. If it is closer to 1, it indicates that the tortuosity of this section of road is greater and the significance is higher; if it is closer to 0, it indicates that the tortuosity of this section of road is smaller and the closer it is to a straight line, the lower the significance.

[0085] (2) Hub selection based on transfer stations

[0086] Transfer stations play a crucial role in connecting two or more subway lines. When creating a subway diagram, using transfer stations as hubs can help maintain the original road conditions of both the main and secondary subway lines.

[0087] For the selection of transfer stations, one method is to judge by the number of grid nodes, and the other is to judge by the degree of the nodes by constructing a network diagram.

[0088] (1) Judging by the number of grid points: The map points are divided into grids based on regular grids. In the divided grids, for each node of each line, there is at most one point in the grid where it is located, that is, the point itself. If there are two or more points in the grid, it indicates that the grid is a transfer station grid, and the transfer station can be found. Each point has a route number attribute. The transfer station grid will record which two or several lines the transfer point belongs to;

[0089] Select the transfer station by the number of nodes of the transfer station, and quickly mark the grid of the transfer station. Figure 1 Transfer station extraction results.

[0090] (2) Judgment by constructing a network graph: Introducing graph theory from discrete mathematics into geographic networks, only three concepts in graph theory are considered, namely, the graph G consisting of a set of nodes and a set of edges, and the number of edges associated with each node, which is the degree of the node;

[0091] For a transfer station, the node degree of an ordinary station should be less than or equal to 2, and the node degree of a transfer station should be greater than or equal to 3. The transfer station is detected by this method.

[0092] (3) Fusion of two pivot point selection methods

[0093] The hub points are selected based on the changes in the tortuosity of the road network, which preserves the shape characteristics of the road network to the greatest extent. However, if the road tortuosity of the station or transfer station is small, it is very likely to be filtered out as an ordinary point, which is not allowed in the production of the schematic diagram.

[0094] Based on the hub point selection of transfer stations, the route is divided. For each divided road, the hub point is selected again, which will better maintain the original characteristics of the road network.

[0095] Therefore, this application combines the two hub point selection methods, and after extracting the transfer stations, simplifies and extracts the nodes and stations between the transfer stations.

[0096] 3. Adaptive Simplification of Road Network Features

[0097] The first and last points of each curve are simulated and connected, and the parametric equation of the connection line is obtained. Then, the distances from all nodes to the straight line are calculated, and the maximum distance between them is obtained and compared with the set critical value limit.

[0098] However, when the curve is complicated, the recursive level is too deep, which may lead to stack overflow, which is a common phenomenon in computers. Therefore, this application adopts a non-recursive approach to optimization.

[0099] To ensure that the extreme points obtained in the middle are not discarded during the processing, the curve is divided into two parts at the extreme point of the bend and processed into two segments. For the extreme point of the bend, the angle between the middle point and the two adjacent vertices is measured. Combined with the stack data structure, a segmentation method is used. Starting from one end of the curve, the first and last points are first identified as the working segments. Then, it is determined whether the distance between the farthest point calculated in the middle is greater than the critical value. In this way, the comprehensive simplification of line features is completed. The specific steps of the improvement are as follows:

[0100] Step 1: Find the point with the largest curvature in the curve, divide the curve into two parts based on this point, and create a point list for each part. Then process the two curves separately.

[0101] Step 2: For the first curve segment, there is a sequence of vector calculated points, forming a line segment, generating a stack, and pushing the points into the stack;

[0102] Step 3: Find the farthest node between the line segments, denoted as C, and the distance is Dist;

[0103] Step 4: Determine whether the distance from the node to the first curve segment is less than a given critical value. If not, add point C to the feature sequence, push the node into the stack, connect the two points with a line segment, and return to step 3. If yes, execute step 5.

[0104] Step 5: Determine whether the node is equal to the top element of the stack. If it is not the top element of the stack, connect the two points and return to step 3. If so, execute step 6.

[0105] Step 6: Determine whether the distance from the node to the second curve segment is greater than a given critical value. If not, set the node to represent the next point on the stack, connect the line segments, pop the top element of the stack, and then return to step 3.

[0106] Step 7: When the stack is empty, the first segment of the curve is finished, and the second segment of the curve is processed in the same way, and steps 1 to 7 are repeated.

[0107] Although the above improved algorithm is relatively complex in terms of program design, it can effectively reduce the number of intermediate repeated loops.

[0108] 4. Artistic Deformation of Road Network Point by Point

[0109] This application establishes a point-by-point transformation method for a road network. For all points, only one transformation is performed without subsequent position changes, that is, the points are transformed to the final generated schematic position in one step;

[0110] When performing point-by-point transformations, consider the following two aspects:

[0111] (1) Transformation area: For the transformed points, other points within a certain buffer range are considered to ensure that their relative positions do not change. Within a certain buffer zone, the transformation methods and transformation equations of all points are consistent, and the point distribution is kept as close to that on the original map as possible;

[0112] (2) Transformation model: For points that have not been transformed, certain point transformations are performed to generate points that meet the direction requirements. For points that have been transformed, the position of the point is guaranteed to remain unchanged, while other points are transformed. If two points in the area have been transformed and the line segment connecting the two points cannot meet the direction requirements of the schematic subway map, a point needs to be interpolated between the two points to meet the eight-direction rule between the points.

[0113] (1) Selecting the local area for transformation

[0114] Based on the node that needs to be transformed, all nodes within a certain range around it are transformed at the same time. The methods for selecting the transformation area in the network construction method include:

[0115] (1 Direction neighborhood index method:

[0116] In image smoothing, for the pixel value of the current point after smoothing calculation, the pixel values of the eight surrounding neighborhoods (i.e., the point's upper, lower, left, right, upper left, lower left, upper right, and lower right) are used to calculate the average value as the output pixel value of the point, and the pixel values of the four points in its four neighborhoods (i.e., the point's upper, lower, left, and right) are used to calculate the average value as the output pixel value of the point; all points in the neighborhood are selected, and these nodes are transformed to maintain the consistency of their topological relationships;

[0117] (2) Neighborhood index of a certain radius buffer:

[0118] The buffer zone is a polygon of a certain width that is automatically established around each node based on the situation analysis required. The data structure of the point is changed to facilitate the neighborhood search and speed up the buffer zone retrieval.

[0119] (2) Transformation of artistic models

[0120] The transformation of point positions is reflected in translation transformation. Translation transformation simply transforms the positions of all nodes of the graph in the same way of movement. It is divided into the following three cases:

[0121] (1) The point to be changed is the node sequence number in the road: the point is the point before the second to last point in the entire point sequence. If it is lower than this, only the current point is changed, and the situation of the next two points does not need to be considered;

[0122] (2) The number of road nodes to be transformed is greater than or equal to three, and the transformation point is the second-to-last node in the entire road. The previous point is a transformed point, and the next point is the end point of the feature. After the transformation of this point, the angles formed by the straight lines between it and the two previous and next points should all satisfy the eight-direction rule;

[0123] (3) When the total number of road nodes to be transformed is two, the first and last points are both feature points and cannot be transformed. In this case, a point needs to be interpolated to satisfy the eight-direction rule.

[0124] There are three situations for point position transformation mentioned above. The design of the transformation model is divided into three parts: the first is the direct transformation of the point to be transformed, the second is the point position transformation taking into account the direction of the previous and next points, and the third is the interpolation transformation of the point position.

[0125] 1. Direct transformation of the point to be transformed:

[0126] Using the rule of constructing an eight-direction map diagram, the points to be transformed are transformed horizontally, vertically, and at 45° angles. Taking one of the cases as an example, the basic principle of the transformation is as follows: Figure 2 As shown in the figure, the nodes outside the line segment are the nodes to be transformed, and the nodes inside the line segment are the nodes that have been transformed. First, the angle between the line segment and the horizontal direction is calculated, the angle is judged, and the projection is made to the direction closest to it. When the angle between the line segment and the horizontal direction is less than 22.5°, the projection to the X-axis is the most appropriate. Therefore, the point to be transformed is projected onto the X-axis to complete the point position transformation.

[0127] At the same time, if the point position is transformed to the 45° direction, there are three processing methods:

[0128] (1) The x-coordinate of the node remains unchanged, and the y-coordinate is transformed and translated to the 45° direction;

[0129] (2) Keep the y coordinate of the point unchanged and transform the x coordinate to move it to the 45° direction;

[0130] (3) Project the point to the 45° direction;

[0131] Based on the need to maintain the consistency of line segment proportions between points, the points are projected to the 45° direction to better maintain the consistency rule of line segment proportions;

[0132] 2. Consider the position change of front and rear points

[0133] The two points before and after the transformation point need to keep their positions unchanged, and the point to be changed after the transformation must satisfy the direction rules of the line segment connecting the two points before and after the transformation, and must satisfy the direction rules of the schematic diagram rules;

[0134] For point position transformation in this case, there are two transformation methods: one is based on four-direction transformation, that is, the point is transformed up, down, left, and right; the other is based on eight-direction transformation, that is, the point is transformed in eight directions: up, down, left, right, upper left, lower left, upper right, and lower right.

[0135] For these two transformation methods, select an optimal transformation. The priority of the optimal transformation point is as follows:

[0136] (1) The topological relationship between the transformed points and other points should be consistent: Topological consistency is the rule for optimal maintenance of schematic maps and is also the basic rule of schematic maps, so this requirement should be the primary requirement;

[0137] (2) The transformed points should keep the position change as small as possible compared with the points before the transformation: Since the schematic map is required to be as similar as possible to the original map when making the schematic map, the spatial distribution of the points should be kept as similar as possible;

[0138] (3) If all the transformed points violate the consistency rule of topological relationship with other points, first find the optimal position according to rule (2), and then perform consistent topological transformation on all points within the range.

[0139] This point transformation method tries to keep the point offset as small as possible before and after the point transformation, and tries to keep the point transformation similar to the original map.

[0140] 3. Interpolation point transformation

[0141] Interpolate a node between two nodes so that the line segment formed by this node and the two nodes before and after it meets the directional rules of the diagram. The transformation method of the same interpolated point is the same as the case of taking into account the point position transformation of the previous and next points. However, during the interpolation process, the following situations need to be considered:

[0142] (1) The interpolated point does not conflict with other points in topology: This situation is relatively simple, and the direction correction is performed directly according to the rule (2) in the case of the position transformation of the previous and next points;

[0143] (2) The interpolated point conflicts with other points in topology: This situation is handled in accordance with item (3) of the case of taking into account the point transformation of the previous and next points;

[0144] In some special cases, if there are no other points between two transfer stations, and the angle formed by these two transfer stations is close to 0°, 45°, or 90°, interpolating the nodes will make the generated road network very fragmented. Therefore, for this special case, this application adopts the method of fine-tuning the transfer stations to meet the direction requirements. When the angle between the straight line formed by the two points and the regular direction is less than , the coordinates of the transfer station to be transformed are fine-tuned, and the other nodes in the grid are also transformed by the transformation function. The value set in this application is 5°.

[0145] (3) Constructing the transformation equation

[0146] Construct a corresponding transformation equation for each node in each transformation area, and formulate the transformation equation into one equation, that is, a total transformation equation. After determining the minimum spatial displacement and neighborhood relationship of the node transformation, the point is offset in combination with the boundary of the point transformation range. The offset is proportional to the ratio of each node to the boundary, maintaining the invariance of the topological relationship of each node before and after the transformation.

[0147] IV. Case Analysis

[0148] Conduct programming experiments on the proposed algorithms and ideas, demonstrate the schematic effects of the algorithms through specific examples, and highlight the feasibility of the algorithm in this application and its advantages over the officially published map diagrams by comparing them with the officially published map diagrams.

[0149] Beijing's rail transit data is used as one of the experimental data. The purpose is to take into account the complexity of its transportation network distribution and the high density of the central urban area, which can further verify the universality of the algorithm in the automatic generation of schematic diagrams in complex scenarios.

[0150] This application compares the map diagram generated by the algorithm using experimental data with the officially published map diagram, showing that it meets the requirements for diagram production in terms of functionality and explaining how it is more reasonable than the official diagram.

[0151] (1) Preparation of a schematic diagram of Beijing's subway lines

[0152] In order to verify the universality of this method, an algorithm experiment was conducted on Beijing's urban rail transit. Beijing's urban rail transit is complex and can better verify the effectiveness of this application algorithm.

[0153] The algorithm sets the grid size to 1m and the value to 5°. The algorithm runs in 20.36 seconds in Visual Studio 2013, Debug platform, and the generated schematic road network is as follows: Figure 4 shown. Figure 3 This is the original map of Beijing's subway rail transit lines. Figure 4 A schematic map of the Beijing subway was generated.

[0154] (2) Explanation of experimental results

[0155] from Figure 4 It can be seen that the schematic map generated by the algorithm of this application fully guarantees the topological relationship of the road network, and can also separate the road network well in the densely populated areas in the center, avoiding the overlap of the road network.

Claims

1. A method for generating an adaptive road network for a schematic artistic map, characterized in that: Based on the grid segmentation method, the nodes are arranged according to the design rules of the schematic map using node transformation and interpolation methods, and the final schematic result is finally generated. For the selection of key stations, a fast method is adopted to extract nodes with transfer stations as the target, and the extracted transfer stations are used as segmentation stations. The features of other stations between transfer stations are extracted to maximize the original characteristics of the line. Finally, the points are translated and interpolated within the buffer grid so that the lines connected by the points in each buffer grid meet the directional design rules of the schematic map. In line simplification, the efficiency of line simplification is improved by optimizing the iterative splitting and merging algorithm. In the node transformation, the transformation status of the points is judged, and the interpolated point positions and relative topological relationships are calculated. First, the map is divided and segmented using a grid segmentation method based on regular grids; The second is the selection rule of the road network hub: the transfer stations are determined by counting the number of various points, and the transfer stations are used as hubs to maintain the skeleton of the network; The third is adaptive simplification of road network features: an optimized non-recursive iterative splitting and combining algorithm is used to simplify lines. The recursive iterative splitting and combining algorithm is converted into a non-recursive iterative splitting and combining algorithm through a stack. Fourth, the road network is artistically deformed point by point: the transformation area is selected through the orientation neighborhood index method, the map is converted into a regular grid map, the selection space of the transformation area is conveniently selected through neighborhood selection, and the construction is assisted by the buffer zone, and the buffer zone is constructed to reorganize the data structure; a road network transformation model is established to analyze the three situations in the road network transformation, and solutions are established for the three situations of direct transformation of points, transformation of points taking into account the front and back points, and interpolation of point transformation; finally, based on the three transformations, a transformation equation is established, and the two parameters of position information and topological transformation information are input. Then, through proportional transformation, each point in the area is translated to the corresponding proportion to realize the road network transformation.

2. The method for generating an adaptive road network for a promotional schematic art map according to claim 1, characterized in that: Generate a schematic grid model: rule-guided grid segmentation, by constructing M×N grids, all sites on the map are stored in grids to facilitate retrieval and grid transformation calculations; 1) Construct an adaptive grid: Use the line name to which the station belongs as the station's attribute number and calculate the rectangular boundary of the map formed by the station, that is, the maximum and minimum values of the horizontal and vertical coordinates of the station. Then count the number of stations and nodes and calculate the size of the grid. Calculate the row and column number of each point in the grid and construct the grid index number 2) Minimize the grid size: Based on the infinite approximation model, a method for minimizing the grid size is established. On the basis of constructing an adaptive grid, the size of the grid is infinitely reduced, and finally the grid is replaced by points for calculation; The minimization method is used to replace the nodes with grids. The original map is drawn based on the real road network. The grid is set to 1 meter. For the thousand-fold reduction change, the grid is replaced by nodes for calculation.

3. The method for generating an adaptive road network for a schematic promotional art map according to claim 1, characterized in that: Hub point selection based on the road network tortuosity fluctuation model: Hub points are selected based on the road network tortuosity fluctuation to better maintain the changes in road graphics. Through tortuosity calculation, areas with high and low road change significance are found. For road sections with high significance, significance is maintained, while for road sections with low significance, significance is not maintained. First, the curvature of each node is calculated. The average value of each node curvature ranges from 0 to 1. The closer it is to 1, the greater the tortuosity change of the road section and the higher the significance. The closer it is to 0, the smaller the winding changes of the road section are, and the closer it is to a straight line, the lower the significance.

4. The method for generating an adaptive road network for a schematic promotional art map according to claim 1, characterized in that: Hub point selection based on transfer stations: transfer stations are used as hub points, maintaining the original road conditions of the main and secondary subway line maps; For the selection of transfer stations, one method is to judge by the number of grid nodes, and the other is to judge by the degree of the nodes by constructing a network graph; (1) Judging by the number of grid points: The map points are divided into grids based on regular grids. In the divided grids, for each node of each line, there is at most one point in the grid where it is located, that is, the point itself. If there are two or more points in the grid, it indicates that the grid is a transfer station grid, and the transfer station can be found. Each point has a route number attribute. The transfer station grid will record which two or several lines the transfer point belongs to; Select transfer stations based on the number of transfer station nodes and mark the transfer station grid; (2) Judgment by constructing a network graph: Introducing graph theory from discrete mathematics into geographic networks, only three concepts in graph theory are considered, namely, the graph G consisting of a set of nodes and a set of edges, and the number of edges associated with each node, which is the degree of the node; For a transfer station, the node degree of an ordinary station should be less than or equal to 2, and the node degree of a transfer station should be greater than or equal to 3. The transfer station is detected by this method.

5. The method for generating an adaptive road network for a schematic promotional art map according to claim 1, characterized in that: Fusion of two hub point selection methods: hub points are selected based on the tortuosity of the road network, preserving the shape characteristics of the road network to the greatest extent possible; Based on the hub point selection of transfer stations, the route is divided. For each divided road, the hub point is selected again, which will better maintain the original characteristics of the road network. The two hub point selection methods are combined. After extracting the transfer stations, the nodes and stations between the transfer stations are simplified and extracted.

6. The method for generating an adaptive road network for a schematic promotional art map according to claim 1, characterized in that: Adaptive simplification of road network characteristics: simulate the connection between the first and last points of each curve, and calculate the parametric equation of the connection line. Then, calculate the distance from all nodes to the straight line, and find the maximum distance between them, and compare it with the set critical value limit.

7. The method for generating an adaptive road network for a schematic promotional art map according to claim 6, characterized in that: A non-recursive optimization method is used: during the processing, the extreme points obtained in the middle are not discarded. The curve is divided into two parts at the extreme point of the bend, and the angle between the extreme point and the two adjacent vertices is measured. In combination with the stack data structure, a segmentation method is used. Starting from one end of the curve, the first and last points are first identified as the working segments. Then, it is determined whether the distance between the farthest points calculated in the middle is greater than the critical value. In this way, the comprehensive simplification of line features is completed. The specific steps of the improvement are as follows: Step 1: Find the point with the largest curvature in the curve, divide the curve into two parts based on this point, and create a point list for each part. Then process the two curves separately. Step 2: For the first curve segment, there is a sequence of vector calculated points, forming a line segment, generating a stack, and pushing the points into the stack; Step 3: Find the farthest node between the line segments, denoted as C, and the distance is Dist; Step 4: Determine whether the distance from the node to the first curve segment is less than a given critical value. If not, add point C to the feature sequence, push the node into the stack, connect the two points with a line segment, and return to step 3. If yes, execute step 5. Step 5: Determine whether the node is equal to the top element of the stack. If it is not the top element of the stack, connect the two points and return to step 3. If so, execute step 6. Step 6: Determine whether the distance from the node to the second curve segment is greater than a given critical value. If not, set the node to represent the next point on the stack, connect the line segments, pop the top element of the stack, and then return to step 3. Step 7: When the stack is empty, the first segment of the curve is finished, and the second segment of the curve is processed in the same way, and steps 1 to 7 are repeated.

8. The method for generating an adaptive road network for a promotional schematic art map according to claim 1, characterized in that: Point-by-point artistic deformation of the road network: A point-by-point transformation method for the road network is established. For all points, only one transformation is performed without subsequent position changes. That is, the points are transformed to the final schematic position in one step; When performing point-by-point transformations, consider the following two aspects: (1) Transformation area: For the transformed points, other points within a certain buffer range are considered to ensure that their relative positions do not change. Within a certain buffer zone, the transformation methods and transformation equations of all points are consistent, and the point distribution is kept as close to that on the original map as possible; (2) Transformation model: For points that have not been transformed, certain point transformations are performed to generate points that meet the direction requirements. For points that have been transformed, the position of the point is guaranteed to remain unchanged, while other points are transformed. If two points in the area have been transformed and the line segment connecting the two points cannot meet the direction requirements of the schematic subway map, a point needs to be interpolated between the two points to meet the eight-direction rule between the points.

9. The method for generating an adaptive road network for a schematic promotional art map according to claim 1, characterized in that: Select local area for transformation: All nodes within a certain range around the node that needs to be transformed are transformed simultaneously. The methods for selecting transformation areas in a network-building manner include: 1) Azimuth neighborhood indexing method: In image smoothing, for the pixel value of the current point after smoothing calculation, the pixel values of the eight surrounding neighborhoods (i.e., the point's upper, lower, left, right, upper left, lower left, upper right, and lower right) are used to calculate the average value as the output pixel value of the point, and the pixel values of the four points in its four neighborhoods (i.e., the point's upper, lower, left, and right) are used to calculate the average value as the output pixel value of the point; all points in the neighborhood are selected, and these nodes are transformed to maintain the consistency of their topological relationships; 2) Neighborhood index of a certain radius buffer: The buffer zone is a polygon of a certain width that is automatically established around each node based on the situation analysis required. The data structure of the point is changed to facilitate the neighborhood search and speed up the buffer zone retrieval.

10. The method for generating an adaptive road network for a schematic promotional art map according to claim 1, characterized in that: Transformation Artistic Model: The transformation of point positions is reflected in translation transformation. Translation transformation is to transform the positions of all nodes of the graph in the same way. It is divided into the following three cases: (1) The point to be changed is the node sequence number in the road: the point is the point before the second to last point in the entire point sequence. If it is lower than this, only the current point is changed, and the next two points are not considered; (2) The number of road nodes to be transformed is greater than or equal to three, and the transformation point is the second-to-last node in the entire road. The previous point is a transformed point, and the next point is the end point of the feature. After the transformation of this point, the angles formed by the straight lines between it and the two previous and next points should all satisfy the eight-direction rule; (3) When the total number of road nodes to be transformed is two, the first and last points are both feature points and cannot be transformed. In this case, a point needs to be interpolated to satisfy the eight-direction rule. There are three situations for point position transformation mentioned above. The design of the transformation model is divided into three parts: the first is the direct transformation of the point to be transformed, the second is the point position transformation taking into account the direction of the previous and next points, and the third is the interpolation transformation of the point position. Direct transformation of the points to be transformed: Using the rule of constructing an eight-direction map diagram, the points to be transformed are transformed horizontally, vertically, and at 45° angles. The nodes outside the line segment are the nodes to be transformed, and the nodes inside the line segment are the transformed nodes. First, the angle between the line segment and the horizontal direction is calculated, the angle is judged, and the point is projected to the direction closest to it. When the angle between the line segment and the horizontal direction is less than 22.5°, it is concluded that the projection to the X-axis is the most appropriate. The point to be transformed is projected onto the X-axis to complete the point transformation of the single point. At the same time, if the point position is transformed to the 45° direction, there are three processing methods: (1) The x-coordinate of the node remains unchanged, and the y-coordinate is transformed and translated to the 45° direction; (2) Keep the y coordinate of the point unchanged and transform the x coordinate to move it to the 45° direction; (3) Project the point to the 45° direction; Based on the need to maintain the consistency of line segment proportions between points, the points are projected to the 45° direction to better maintain the line segment proportion consistency rule.

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