Three-dimensional road model generation method and system based on maximum smoothing strategy

Abstract

The application provides a three-dimensional road model generation method and system based on a maximum smoothing strategy, comprising: acquiring point data in GIS data; filtering the point data, and analyzing a current optimal solution from a local topological structure to a global topological structure; according to the optimal solution, acquiring a structure with the smallest radius to perform smoothing processing on a current road to complete curve fitting; and combining a spatial structure of the road and a corresponding strategy to further generate a three-dimensional road. The application automatically generates a 3D road semantic structure in a large scale through sparse road network GIS data, which conforms to road national standard specifications and can be used for traffic simulation, improves the degree of automatic generation, and generates a three-dimensional road network road which is continuous in height through cubic spline interpolation of a fixed boundary, thereby improving the visual effect of the road, enhancing the reality of the road, and conforming to highway design standards.

Description

Technical Field

[0001] This invention relates to the field of 3D reconstruction and road simulation technology, specifically to a method and system for generating 3D road models based on a maximum smoothness strategy. Background Technology

[0002] Virtual 3D road networks can provide highly immersive visualization effects for virtual simulation worlds and are an important part of traffic simulation and intelligent traffic control. How to generate large-scale 3D roads that include realistic scenes, smooth roads and road traffic semantics is the key to immersive and reliable traffic simulation.

[0003] In traditional fields, using 3D models to generate 3D road scenes is a common method. By obtaining the number of lanes, detailed parameters of intersections, and road elevation data, these are input into modeling software to reconstruct large-scale 3D road scenes. However, this method is difficult to keep consistent with the road in satellite imagery in terms of location and texture, and requires a lot of manual statistical work, resulting in low automation and a large workload.

[0004] With the development of remote sensing satellite technology, generating 3D road networks from satellite imagery and GIS data has become more realistic and efficient. Traditional machine learning and deep learning methods can perform semantic segmentation on satellite imagery, extracting road centerlines, widths, and intersection shapes. While this extracted data supports 3D reconstruction, it lacks elevation data, preventing true 3D road reconstruction. Furthermore, trees and shadows in satellite imagery obstruct road segmentation, affecting its accuracy. GIS data can annotate road nodes, allowing for rapid network generation. However, these networks are often not smooth and do not meet national road standards. Therefore, many smoothing curve algorithms, such as cubic splines and Bézier curves, are applied to smooth road generation. While visually acceptable, these designs are not standard in national road standards and contradict vehicle kinematics.

[0005] Currently, existing technologies for extracting road centerline data from GIS data require analyzing the entire road network data to separate intersections and individual roads. The steps are as follows: 1. Sequentially find a road node A with a degree of 1. 2. Starting from node A, search for nodes B with a degree greater than 2 or equal to 1. If the degree is greater than 2, AB is a simple road, and B is an intersection. Then, starting from B, search in other directions, skipping to step 1. If the degree is equal to 1, AB is a simple road, and then sequentially search for other nodes with a degree of 1. 3. Steps 1 and 2 filter out all roads and intersections in the road network. Intersections are combined with edge feature points to construct a triangular mesh, and corresponding textures are applied using satellite imagery. By combining discrete points in the roads, straight-line-circular curves or Bézier curves are used to smooth each curve inflection point. 4. GIS data provides road hierarchy information, allowing determination of the road node's trend. Two-dimensional roads can be linearly interpolated in height to generate three-dimensional roads.

[0006] However, road smoothing techniques using a straight-to-circular-curve model require precise curve information to determine the start and end points of the circular curve. In large-scale road generation, curve or road curve information is difficult to obtain from GIS data, requiring manual measurement and input, which is clearly unsuitable for large-scale automated road network generation. Using Bézier curves, on the other hand, does not conform to realistic road design standards, and the computational load for Bézier curves on roads with multiple inflection points is substantial.

[0007] In summary, the existing technology has the following shortcomings: low degree of automation in road generation, poor realism of generated roads, and the three-dimensional roads do not conform to the physical laws of vehicle movement. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method and system for generating three-dimensional road models based on the maximum smoothness strategy.

[0009] In a first aspect, the present invention provides a method for generating a three-dimensional road model based on a maximum smoothing strategy, comprising: Step S1: Obtain point data from the GIS data; Step S2: Filter the point data and analyze the current optimal solution from the local topology to the global topology; Step S3: Based on the optimal solution, obtain the structure with the smallest radius to smooth the current road and complete the curve fitting; Step S4: Combine the spatial structure of the road with the corresponding strategies to generate a three-dimensional road.

[0010] Preferably, the smoothing process includes: dividing the road into multiple segments according to the curves, with each curve point having a vertex. Pi Then generate the corresponding radius as r i The arc is optimized by maximizing the minimum value of all radii. The optimization formula is as follows:

[0011] in, n Indicates the number of arcs.

[0012] Preferably, the optimized formula is calculated as follows:

[0013]

[0014] In the formula, Indicates the first i The radius of an arc, Indicates the first i An arc angle Indicates the first i The road sacrifice length corresponding to each arc Representing data points P i+1 To data point P i The distance; Analyze the local topology, assuming the local topology includes... P i-1 , P i ,P i+1 and P i+2 ,because and Proportional, therefore:

[0015] according to Then we have:

[0016]

[0017]

[0018] Conclusion:

[0019] Therefore, we can conclude that:

[0020]

[0021] From the above formula, we can obtain The maximum value is determined by a fixed value, which reflects the basic elements of the current topological relationship, and it is known that... Therefore, we can conclude that:

[0022]

[0023] achievable The range of values ​​for is:

[0024] This can be satisfied within the local topology.

[0025] Preferably, from the optimal solution of the local topology to the optimal solution of the global topology, a structure with the smallest radius is selected in each optimal solution of the local topology, and the other road sacrifice lengths are recursively calculated according to the bisection method.

[0026] Preferably, after smoothing, denser data points are generated on a two-dimensional plane, and combined with the spatial structure of the road and corresponding strategies, a three-dimensional road is generated. The strategy includes the following: the minimum value between the starting point and the ending point of the current road. layer When all attributes are 0, and the road has no attributes. layer The attribute indicates that this is a road that hugs the ground; if the road has layer The attribute indicates that this is a bridge with its starting and ending points close to the ground and a raised section in the middle; the minimum starting and ending points of the current road. layer If any attribute is not 0, then the road is a bridge with an upward or downward trend.

[0027] Secondly, the present invention provides a three-dimensional road model generation system based on a maximum smoothness strategy, comprising: Module M1: Retrieves point data from GIS data; Module M2: Filters the point data and analyzes the current optimal solution from the local topology to the global topology; Module M3: Based on the optimal solution, obtain the structure with the smallest radius to smooth the current road and complete curve fitting; Module M4: Combines the spatial structure of the road with corresponding strategies to generate a three-dimensional road.

[0028] Preferably, the smoothing process includes: dividing the road into multiple segments according to the curves, with each curve point having a vertex. P i Then generate the corresponding radius as r iThe arc is optimized by maximizing the minimum value of all radii. The optimization formula is as follows:

[0029] in, n Indicates the number of arcs.

[0030] Preferably, the optimized formula is calculated as follows:

[0031]

[0032] In the formula, Indicates the first i The radius of an arc, Indicates the first i An arc angle Indicates the first i The road sacrifice length corresponding to each arc Representing data points P i+1 To data point P i The distance; Analyze the local topology, assuming the local topology includes... P i-1 , P i ,P i+1 and P i+2 ,because and Proportional, therefore:

[0033] according to Then we have:

[0034]

[0035]

[0036] Conclusion:

[0037] Therefore, we can conclude that:

[0038]

[0039] From the above formula, we can obtain The maximum value is determined by a fixed value, which reflects the basic elements of the current topological relationship, and it is known that... Therefore, we can conclude that:

[0040]

[0041] achievable The range of values ​​for is:

[0042] This can be satisfied within the local topology.

[0043] Preferably, from the optimal solution of the local topology to the optimal solution of the global topology, a structure with the smallest radius is selected in each optimal solution of the local topology, and the other road sacrifice lengths are recursively calculated according to the bisection method.

[0044] Preferably, after smoothing, denser data points are generated on a two-dimensional plane, and combined with the spatial structure of the road and corresponding strategies, a three-dimensional road is generated. The strategy includes the following: the minimum value between the starting point and the ending point of the current road. layer When all attributes are 0, and the road has no attributes. layer The attribute indicates that this is a road that hugs the ground; if the road has layer The attribute indicates that this is a bridge with its starting and ending points close to the ground and a raised section in the middle; the minimum starting and ending points of the current road. layer If any attribute is not 0, then the road is a bridge with an upward or downward trend.

[0045] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention automatically generates 3D road semantic structures that conform to national road standards and can be used for traffic simulation on a large scale using sparse road network GIS data. It generates these structures directly from existing sparse GIS data, requiring no additional input and thus improving the level of automation.

[0046] 2. The road proposed in this invention combines straight lines and circular curves. Based on the maximum smoothness strategy, it automatically generates two-dimensional smooth roads that meet highway standards. Furthermore, it performs three-dimensional transformation through cubic spline interpolation with fixed boundaries, generating a three-dimensional road network that is continuous in height. This improves the visual effect of the road and enhances its realism.

[0047] 3. The road parameterization of this invention is reasonable, provides vehicle position calculation, and the road design matches the vehicle's kinematic model, which meets highway design standards. Attached Figure Description

[0048] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the workflow of the present invention.

[0049] Figure 2 This is a polyline graph input into the GIS system in this invention.

[0050] Figure 3 This is a geometric curve diagram after smoothing in this invention.

[0051] Figure 4 This is a diagram illustrating the effect of using arcs to replace internal vertices in this invention.

[0052] Figure 5 This is a schematic diagram of a local topology in this invention.

[0053] Figure 6 This is the original polyline road curve diagram of the GIS data in this invention, without any processing.

[0054] Figure 7 This is a diagram showing the result of the improved polyline smoothing algorithm in this invention.

[0055] Figure 8 This is a schematic diagram showing the connection between a regular road and an overpass in this invention, and a comparison of the improved effect after the invention.

[0056] Figure 9 This is a schematic diagram showing a complex traffic scene at an overpass in this invention and a comparison of the improved effect after the invention.

[0057] Figure 10 This is a schematic diagram of the bridge and road structure with both ends touching the ground in this invention, and the effect after improvement by this invention.

[0058] Figure 11 This is a schematic diagram showing a visual comparison between a real road and a virtual simulation system in this invention. Detailed Implementation

[0059] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0060] Example 1 According to the present invention, a method for generating a 3D road model based on a maximum smoothness strategy is provided, such as... Figure 1 As shown, it includes: Step S1: Obtain point data from the GIS data. The point data is defined as follows: As shown. These point data define a... n A broken line segment with a length of -1, such as Figure 2 As shown.

[0061] Step S2: Filter the point data and analyze the current optimal solution from the local topology to the global topology. Specifically, filter the original point data in the collected GIS data so that there are no two points with the same location in the filtered GIS sequence, and no three points collinear.

[0062] Step S3: Based on the optimal solution, obtain the structure with the smallest radius to smooth the current road and complete curve fitting. That is, replace each interior point of the curve with a generated arc. P i And leave the point before that internal point. P 0 and the point after that interior point P n-1 To construct such Figure 3 The curve shown. Specifically, the smoothing process includes dividing the road into multiple segments based on turns, with each turn point having a vertex. P i Then generate the corresponding radius as r i The arc is optimized by maximizing the minimum value of all radii. The optimization formula is as follows:

[0063] in, n This represents the number of arcs. By maximizing the minimum value of all selected radii, the generated curve will have the best visual smoothness, minimizing the sharpness of each inflection point. Specifically, a local-to-global approach generates each radius that satisfies the optimization formula. ,like Figure 4 As shown, each arc corresponds to an interior point. Pi Then make the arc with P i-1 , P i ,P i+1 Tangent; to further simplify the problem, this invention introduces a key auxiliary variable. ,like Figure 5 As shown. Further, the optimized formula is calculated as follows:

[0064]

[0065] In the formula, Indicates the first i The radius of an arc, Indicates the first i An arc angle Indicates the first i The road sacrifice length corresponding to each arc Representing data points P i+1 To data point P i The distance.

[0066] Analyze the local topology, such as Figure 5 As shown, the local topology includes P i-1 , P i ,P i+1 and P i+2 ,because and Proportional, and according to We can obtain:

[0067] according to Then we have:

[0068]

[0069]

[0070] Conclusion:

[0071] Therefore, we can conclude that:

[0072]

[0073] From the above formula, we can obtain The maximum value is determined by a fixed value, which reflects the basic elements of the current topological relationship, and it is known that... Therefore, we can conclude that:

[0074]

[0075] Therefore, we can obtain The range of values ​​for is:

[0076] At this point, the optimization formula can be satisfied within the local topology. (Due to the definition...) = = 0, when i = 0, the formula does not need to be considered. When i = n-1, the formula is not considered. The rest is balanced by the radius. RADIUS-BALACNE The algorithm is given.

[0077] From the optimal solution of the local topology to the optimal solution of the global topology, this invention includes a solution process defined by the assign-alpha function, in which the structure with the smallest radius is selected in each local topology optimal solution, and the other road sacrifice lengths are recursively calculated according to the bisection method.

[0078] Furthermore, such as Figure 6 and Figure 7 As shown, Figure 6 It is the raw, unprocessed polyline road curve from GIS data. Figure 7 This is the result of an improved polyline smoothing algorithm of this invention, where the shaded portion represents the center and radius of each arc used to smooth the road. Curved roads are particularly well-suited for vehicle motion; for example, their prescribed turning behavior matches the kinematic model of a simple car.

[0079] Step S4: Combining the spatial structure of the road with corresponding strategies, a 3D road is generated. After smoothing, denser data points are generated on the 2D plane. Combined with the spatial structure of the road and corresponding strategies, a 3D road is then generated. Specifically, the "way" field provided by OSM (OpenStreetMap) contains... layer The field provides road hierarchy information; if a road does not have a hierarchy, it means that the road is not properly leveled. layer The field indicates that the road should be flush with the ground. Therefore, the strategy includes the following: First strategy: Minimize the minimum of the starting and ending points of the current road. layer When all attributes are 0, and the road has no attributes. layer The attribute indicates that this is a road that hugs the ground.

[0080] Second strategy: Minimize the starting and ending points of the current road layer When all attributes are 0, and the road has layer The attribute indicates that this is a bridge with its starting and ending points close to the ground and a raised section in the middle.

[0081] Third strategy: Minimize the starting and ending points of the current road layer If any attribute is not 0, then the road is a bridge with an upward or downward trend.

[0082] Based on the strategies above, in the first strategy, the road needs to be close to the ground. The local coordinates of the current road data points are converted into latitude, longitude, and altitude, and the elevation information of the current terrain can be obtained based on latitude and longitude to fill the local coordinate height information. Therefore, when the discrete data points are dense enough, the road can be made close to the ground. The construction of roads in the second and third strategies involves the problem of smooth continuity in the height direction. By using the discrete approximation representation in road smoothing, cubic spline interpolation is used to generate C2-continuous three-dimensional roads in height. However, in the process of constructing three-dimensional roads, the transition between roads also needs to be considered. A cubic spline interpolation technique with fixed boundaries can be adopted, fixing the derivatives of the road's start and end points to 0, so that it transitions smoothly and tangentially to the ground.

[0083] Furthermore, by selecting several typical problematic roads in 3D road generation, the problems of each type of road are explained, and the visual effects and rationality of the roads before and after improvement are compared and displayed. Next, a comparison between the model road and a real road is shown to illustrate the realism of the 3D road generation technology. For example... Figure 8 As shown, from Figure 8 The left image shows the junction between the ordinary road and the overpass. There is a break at the junction, and part of the overpass is still touching the ground. Figure 8 The right image shows that the improved 3D road junctions are smoothly connected, and there is a clear upward trend after the overpass, which matches the actual situation. Figure 9 As shown, Figure 9 The left image shows a very complex overpass structure in Shenzhen. The 3D modeling results show that the road height is not smooth and does not conform to the laws of vehicle movement. The height C2 is a continuous road. Figure 9 The right image shows the improved interchange, which not only has a clear hierarchical structure and smooth upward and downward trends, but also exhibits good traffic conditions at the interchange intersections.

[0084] like Figure 10 As shown, Figure 10 The left image shows an elevated bridge that rises and then falls. Current technology cannot distinguish the bridge structure at both ends that are close to the ground, resulting in an incorrect overlap of the three-dimensional road. Figure 10 The right image shows the improved interchange, which not only has a clear hierarchical structure and smooth upward and downward trends, but also exhibits good traffic conditions at the interchange intersections. Figure 11 The image shows a visual comparison between real-world roads and 3D roads modeled in a virtual simulation system. It can be seen that the basic topological structures are similar, the overall layers are distinct, and the intersections of roads can generate structures that are basically consistent with real-world roads.

[0085] Example 2 The present invention also provides a three-dimensional road model generation system based on the maximum smoothing strategy. Those skilled in the art can implement the three-dimensional road model generation system based on the maximum smoothing strategy by executing the steps of the method. That is, the method of generating three-dimensional road models based on the maximum smoothing strategy can be understood as a preferred embodiment of the three-dimensional road model generation system based on the maximum smoothing strategy.

[0086] A three-dimensional road model generation system based on a maximum smoothness strategy, provided by the present invention, includes: Module M1: Retrieves point data from GIS data.

[0087] Module M2: Filters the point data and analyzes the current optimal solution from local to global topology. From the optimal solution of the local topology to the optimal solution of the global topology, it selects the structure with the smallest radius in each local optimal solution and recursively calculates the other road sacrifice lengths using a bisection method.

[0088] Module M3: Based on the optimal solution, obtain the structure with the smallest radius to smooth the current road and complete curve fitting. The smoothing process includes: dividing the road into multiple segments according to turns, with each turn point having a vertex. P i Then generate the corresponding radius as r i The arc is optimized by maximizing the minimum value of all radii. The optimization formula is as follows:

[0089] in, n Indicates the number of arcs.

[0090] Preferably, the optimized formula is calculated as follows:

[0091]

[0092] In the formula, Indicates the first i The radius of an arc, Indicates the first i An arc angle Indicates the first i The road sacrifice length corresponding to each arc Representing data points P i+1 To data point P i The distance.

[0093] Analyze the local topology, assuming the local topology includes... P i-1 , P i ,P i+1 and P i+2 ,because and Proportional, therefore:

[0094] according to Then we have:

[0095]

[0096]

[0097] Conclusion:

[0098] Therefore, we can conclude that:

[0099]

[0100] From the above formula, we can obtain The maximum value is determined by a fixed value, which reflects the basic elements of the current topological relationship, and it is known that... Therefore, we can conclude that:

[0101]

[0102] achievable The range of values ​​for is:

[0103] This can be satisfied within the local topology.

[0104] Module M4: Combines the spatial structure of the road with corresponding strategies to generate a 3D road. After smoothing, denser data points are generated on a 2D plane. Combined with the road's spatial structure and corresponding strategies, a 3D road is then generated. The strategies include: the minimum value between the starting and ending points of the current road. layer When all attributes are 0, and the road has no attributes. layer The attribute indicates that this is a road that hugs the ground; if the road has layerThe attribute indicates that this is a bridge with its starting and ending points close to the ground and a raised section in the middle; the minimum starting and ending points of the current road. layer If any attribute is not 0, then the road is a bridge with an upward or downward trend.

[0105] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0106] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for generating 3D road models based on a maximum smoothness strategy, characterized in that, include: Step S1: Obtain point data from the GIS data; Step S2: Filter the point data and analyze the current optimal solution from the local topology to the global topology; Step S3: Based on the optimal solution, obtain the structure with the smallest radius to smooth the current road and complete the curve fitting; Step S4: Combine the spatial structure of the road with the corresponding strategies to generate a three-dimensional road; The smoothing process includes dividing the road into multiple segments based on turns, with each turn point having a vertex. P i Then generate the corresponding radius as r i The arc is optimized by maximizing the minimum value of all radii. The optimization formula is as follows: in, n Indicates the number of arcs; The optimized formula is calculated as follows: In the formula, Indicates the first i The radius of an arc, Indicates the first i An arc angle Indicates the first i The road sacrifice length corresponding to each arc Representing data points P i+1 To data point P i The distance; Analyze the local topology, assuming the local topology includes... P i-1 , P i ,P i+1 and P i+2 ,because and Proportional, therefore: according to Then we have: Conclusion: Therefore, we can conclude that: From the above formula, we can obtain The maximum value is determined by a fixed value, which reflects the basic elements of the current topological relationship, and it is known that... Therefore, we can conclude that: achievable The range of values ​​for is: This condition is satisfied within the local topology.

2. The method for generating a 3D road model based on the maximum smoothness strategy according to claim 1, characterized in that, From the optimal solution of the local topology to the optimal solution of the global topology, select the structure with the smallest radius in each local optimal solution, and recursively calculate the sacrifice length of other roads according to the bisection method.

3. The method for generating a 3D road model based on the maximum smoothness strategy according to claim 1, characterized in that, After smoothing, denser data points are generated on a two-dimensional plane. Combined with the spatial structure of the road and corresponding strategies, a three-dimensional road is then generated. The strategy includes the following: the minimum value between the starting point and the ending point of the current road. layer When all attributes are 0, and the road has no attributes. layer The attribute indicates that this is a road that hugs the ground; if the road has layer The attribute indicates that this is a bridge with its starting and ending points close to the ground and a raised section in the middle; the minimum starting and ending points of the current road. layer If any attribute is not 0, then the road is a bridge with an upward or downward trend.

4. A three-dimensional road model generation system based on a maximum smoothness strategy, characterized in that, include: Module M1: Retrieves point data from GIS data; Module M2: Filters the point data and analyzes the current optimal solution from the local topology to the global topology; Module M3: Based on the optimal solution, obtain the structure with the smallest radius to smooth the current road and complete curve fitting; Module M4: Combines the spatial structure of the road with corresponding strategies to generate a three-dimensional road; The smoothing process includes dividing the road into multiple segments based on turns, with each turn point having a vertex. P i Then generate the corresponding radius as r i The arc is optimized by maximizing the minimum value of all radii. The optimization formula is as follows: in, n Indicates the number of arcs; The optimized formula is calculated as follows: In the formula, Indicates the first i The radius of an arc, Indicates the first i An arc angle Indicates the first i The road sacrifice length corresponding to each arc Representing data points P i+1 To data point P i The distance; Analyze the local topology, assuming the local topology includes... P i-1 , P i ,P i+1 and P i+2 ,because and Proportional, therefore: according to Then we have: Conclusion: Therefore, we can conclude that: From the above formula, we can obtain The maximum value is determined by a fixed value, which reflects the basic elements of the current topological relationship, and it is known that... Therefore, we can conclude that: achievable The range of values ​​for is: This condition is satisfied within the local topology.

5. The three-dimensional road model generation system based on the maximum smoothness strategy according to claim 4, characterized in that, From the optimal solution of the local topology to the optimal solution of the global topology, select the structure with the smallest radius in each local optimal solution, and recursively calculate the sacrifice length of other roads according to the bisection method.

6. The three-dimensional road model generation system based on the maximum smoothness strategy according to claim 4, characterized in that, After smoothing, denser data points are generated on a two-dimensional plane. Combined with the spatial structure of the road and corresponding strategies, a three-dimensional road is then generated. The strategy includes the following: when the minimum layer attribute of the starting point and the ending point of the current road is 0, and the road has no layer attribute, it means that this is a road that is close to the ground; if the road has a layer attribute, it means that this is a bridge with the starting point and the ending point close to the ground and the middle protruding; if either the minimum layer attribute of the starting point or the ending point of the current road is not 0, then the road is a bridge with an upward or downward trend.

Images