Channel plane boundary separation method based on Delaunay triangle

Abstract

The invention relates to a channel plane boundary separation method based on a Delaunay triangle, and belongs to the field of channel surveying and mapping and channel maintenance. The method comprises the following steps: dynamically correcting a water depth point in a channel topographic mapping to obtain an actual water depth; a water depth point with the actual water depth equal to the channel maintenance water depth serves as a boundary point, and a boundary point set is formed; adding the boundary point set to the original water depth data set, reconstructing a Delaunay triangulation network, screening out all triangles of which the actual water depth is greater than or equal to the channel maintenance water depth, and obtaining a triangular region set; counting the occurrence frequency of each edge of the triangles in the triangular region set, and adding the triangular edges representing region boundaries into a boundary set; and searching edges capable of forming a closed area in the boundary set, combining the edges into a plurality of independent closed polygons, namely channel plane boundaries, and removing holes contained in the largest closed polygon to separate to obtain a channel navigable water depth area range.

Description

Technical Field

[0001] The invention belongs to the field of waterway surveying and maintenance, and relates to a waterway plane boundary separation method based on Delaunay triangulation. Background Art

[0002] As an indispensable and important facility in the waterway, navigation marks obstacles and indicates the navigable area that meets the water depth of the waterway, providing a safe, economical and convenient channel for water transportation. The underwater riverbed terrain of inland waterways is complex, and the water level changes frequently, especially during the flood season and the dry season. The water level fluctuates greatly, resulting in most navigation marks no longer being in the best navigation position. Therefore, it is necessary to adjust the position of navigation marks in combination with water level and topographic mapping to ensure that the navigation marks can timely reflect the changes in the water depth of the waterway and correctly mark the boundaries of the navigable area.

[0003] In the traditional work process, the staff mainly judges whether the current position of the navigation mark is reasonable based on the previous experience of navigation mark distribution and the change of water level. This navigation mark position verification method relies heavily on manual experience, is limited by work attitude and business skills, has low work efficiency, low accuracy, and is prone to miss the reefs and other obstructions in the channel, and the quality cannot be well guaranteed.

[0004] The patent application with publication number CN102982494A discloses a method for generating water depth information of a waterway based on an electronic navigation chart and water level data. The method mainly includes setting the reference surface information of the water depth point on the navigation chart; dynamically correcting the water depth value according to the measured and predicted water level information released by the water level station along the river and the reference surface information of the electronic navigation chart to obtain the absolute water depth value; extracting isobaths according to the absolute water depth value; calculating the navigable area and dynamic center line of the specified depth according to the depth interval of the isobaths, and publishing the generated water depth information through WebService. The method is based on the electronic navigation chart and calculates the navigable area by extracting isobaths. In the specific implementation process, the isobaths are extracted by absolute water depth and converted into polygons (the water depth value is taken at the center point of the polygon), and the navigable water depth area and dynamic center line of the specified depth are cut out by the map frame. The method uses isobaths with an interval of 0.1 meters to divide the navigable area, which cannot accurately depict the regional boundaries and is not accurate enough. Moreover, this solution cannot realize the automatic extraction and separation of navigable water depth areas and obstruction areas. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for separating plane boundaries of a channel based on Delaunay triangulation, which is based on channel topographic mapping, and extracts the plane boundaries of the channel by reading the measurement data in the channel topographic mapping, combining the measured water level or the predicted water level, and utilizing the relationship between vertices, edges and triangles in the triangulation network, and completes the segmentation of the channel boundary by eliminating holes, and generates navigable water depth areas and obstruction areas, so as to assist staff in decision-making and analysis, save labor, improve the accuracy of channel boundary extraction, effectively improve work efficiency, and realize a more scientific and reasonable channel water depth verification.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for separating waterway plane boundaries based on Delaunay triangulation, the method comprising:

[0008] S1. Use the measured water level or predicted water level data to dynamically correct the water depth points in the channel topographic map to obtain the actual water depth;

[0009] S2. After obtaining the actual water depth, extract the boundary points of the river channel to obtain the river channel area that meets the specified water depth, wherein the water depth point where the actual water depth is equal to the waterway maintenance water depth is taken as the boundary point, and a boundary point set is formed;

[0010] S3, adding the boundary point set to the original water depth data set, reconstructing the Delaunay triangulation, screening out all triangles whose actual water depth is greater than or equal to the waterway maintenance water depth, and obtaining a set of triangular areas that meet the waterway maintenance water depth;

[0011] S4, counting the number of occurrences of each edge of the triangle in the triangular region set, and adding the triangular edge representing the region boundary to the boundary set;

[0012] S5, finding edges in the boundary set that can form a closed area, and merging these edges into multiple closed polygons to obtain the waterway plane boundary;

[0013] S6. Eliminate the holes (i.e., the obstruction area, or the reef area) in the largest closed polygon in the plane boundary of the channel, that is, separate and obtain the navigable water depth area of ​​the channel. Among them, the largest closed polygon is the navigable area in the plane boundary of the channel.

[0014] Furthermore, in step S1, the method of obtaining the actual water depth includes:

[0015] According to the calculation formula of actual water depth:

[0016] D=W+D ρ +Δh

[0017] Where D represents the actual water depth, Dρ represents the water depth shown in the figure, W represents the measured water level value, and Δh represents the difference between the water level reference plane and the depth reference plane;

[0018] The weekly forecast maintenance water depth is D U , the water depth shown below the measured water level W is recorded as D W ; The actual water depth D in the navigable water depth area needs to satisfy D ≥ D U , then the water depth D is obtained as shown in the figure W Need to meet: D W ≥D U -W-Δh, thus achieving the water depth D shown in the figure W Dynamic correction of

[0019] According to the corrected water depth D W Calculate the actual water depth D.

[0020] Further, in step S2, the method of extracting boundary points includes: obtaining a set of illustrated water depth points in the waterway topographic map, establishing a plane coordinate system, and constructing a Delaunay triangulation network based on the illustrated water depth point set, storing the adjacency relationship between the edges and vertices of the triangles to establish a topological relationship;

[0021] By setting a triangle length threshold, narrow and long triangles with too large area are eliminated;

[0022] Set channel maintenance water depth D w For any triangle in the triangulation network, if any two vertices in the triangle satisfy: the water depth of one vertex is greater than D w , the water depth of the other vertex is less than D w ; Then there is a point K in the line segment between these two vertices, and the actual water depth D of point K K =D w , the point K is the boundary point; the coordinates of point K are calculated by linear interpolation;

[0023] Traverse all triangles in the triangulated network and obtain the boundary points in the above manner to form a boundary point set.

[0024] Furthermore, step S3 specifically includes adding the boundary point set to the original water depth data set, and reconstructing the Delaunay triangulation based on the original water depth data set;

[0025] By setting a triangle length threshold, narrow and long triangles with too large area are proposed to optimize the triangulated network;

[0026] Set channel maintenance water depth D w If there is a triangle in the triangulation network, the water depths of the three vertices are greater than or equal to D w , then the triangle meets the screening requirements;

[0027] Traverse the triangulated network and filter out all triangles that meet the screening requirements to form a triangular area set.

[0028] Furthermore, step S4 specifically includes counting the number of occurrences of all triangle edges in the triangle region set, and adding the triangle edges whose number of occurrences is 1 to the boundary set.

[0029] Further, step S5 is specifically that the method of finding the edge in the boundary set that can form a closed area includes: obtaining any edge L1 in the boundary set, and connecting its two end points L 1a , L 1b Add to a closed region set P1; if there is another edge L2 in the boundary set, and L1 and L2 have a common endpoint L 1b , then add the non-public endpoints in edge L2 to the closed area set P1; continue to search for edge L3 that has a common endpoint with edge L2, and add the non-public endpoints of edge L3 to the closed area set P1, and traverse all edges in the boundary set until there is no edge that meets the conditions in the boundary set. At this time, the first and last points in the closed area set P1 are the same, and the associated edges of the points in P1 form a closed polygon;

[0030] Create a closed region set P2, find common endpoints for the remaining edges in the boundary set, and classify all edges in the same way as above to obtain a closed region set P = {P1, P2, ..., P n}, the plane boundary of the channel is obtained.

[0031] Further, step S6 is specifically as follows: for any closed area set P i , there may be an intersection point P i It is divided into several small closed areas, and ships are not supported between the sub-areas. Without considering the same head and tail, each point appears only once; therefore, the tail endpoint in the boundary set is removed, and the point that appears more than once is the intersection of the closed area.

[0032] If there is an intersection within the maximum closed polygon, the area between the two occurrences of the same intersection is extracted to form a closed interval, and the remaining points constitute a closed interval; each closed interval is traversed in a loop until there is no intersection in any closed interval, and the decomposition is completed. All closed intervals obtained by decomposition constitute the navigable water depth area of ​​the channel.

[0033] The beneficial effects of the present invention are as follows: the present invention utilizes the survey data and water level data in topographic mapping, and through dynamically correcting the water depth values ​​of the illustrated water depth points, screens out water depth boundary points that meet the conditions, and forms a waterway plane boundary; and utilizes polygon adjacency relationships to complete the identification and separation of navigable water depth areas and obstruction areas. Based on the separation of the waterway plane boundary, the accurate characterization of the navigable water depth area can be achieved, which effectively improves the quality of waterway boundary extraction, enables staff to better complete waterway boundary extraction and navigation mark distribution, and effectively improves work efficiency.

[0034] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0036] Figure 1 A schematic diagram of a flow chart of a method for separating waterway plane boundaries proposed in an embodiment of the present invention;

[0037] Figure 2 It is a schematic diagram of water depth from the perspective of river cross section;

[0038] Figure 3 is the original triangulation diagram;

[0039] Figure 4 This is a schematic diagram of water depth boundary points;

[0040] Figure 5 This is a schematic diagram of the waterway plane boundary. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0042] The present invention provides a method for separating waterway plane boundaries based on Delaunay triangulation, the method comprising:

[0043] 1) Use the measured water level or predicted water level data to dynamically correct the water depth points in the channel topographic map to obtain the actual water depth.

[0044] 2) After obtaining the actual water depth, the water depth points where the actual water depth is equal to the channel maintenance water depth constitute the boundary point set. Delaunay triangulation is performed on the discrete points, and the triangle edges that satisfy one vertex greater than the channel maintenance water depth and another vertex less than the channel maintenance water depth are screened out. The points on the edge that are equal to the channel maintenance water depth are obtained by linear interpolation and added to the boundary point set.

[0045] 3) Add the boundary point set to the original water depth dataset, reconstruct the Delaunay triangulation, filter out all triangles whose actual water depth is greater than or equal to the waterway maintenance depth, and obtain the set of triangular areas that meet the waterway maintenance depth.

[0046] 4) Count the number of occurrences of each edge of the triangle in the triangular area set, and add the triangular edges representing the area boundary to the boundary set; find the edges that form the closed area in the boundary set, and these edges can be merged into a closed polygon, that is, the channel plane boundary is obtained.

[0047] 5) Within the plane boundary of the waterway, there is a closed area with the largest area, namely the navigable water depth area. The navigable water depth area may contain some holes, which constitute the obstruction area. Based on the separation of the plane boundary of the waterway, the accurate characterization of the navigable water depth area can be achieved to assist the staff to better complete the extraction of waterway boundaries and the distribution of navigation marks.

[0048] In one embodiment of the present invention, the implementation method of the present invention is explained by taking the daily maintenance of navigation marks in the area under the jurisdiction of the waterway department as an example. The real-time water level data of the digital waterway and the waterway topographic mapping of the jurisdiction area are combined to dynamically correct the illustrated water depth. Then, according to the waterway maintenance water depth released by the waterway department, accurate water depth boundary points that meet the conditions are drawn, and the plane boundary of the waterway is extracted by using the relationship between vertices, edges and triangles in the triangulated network. The polygon adjacency relationship is used to complete the identification and separation of navigable water depth areas and obstruction areas.

[0049] It can be automatically realized by using computer software technology. The staff only needs to import the channel topographic map of the corresponding area and input the required channel maintenance scale, and the system can automatically output the final navigable water depth area and obstruction area.

[0050] like Figure 1 As shown, this embodiment includes the following steps:

[0051] 1. Graphical water depth threshold

[0052] like Figure 2As shown in the figure, water depth is divided into absolute water depth and relative water depth. Among them, absolute water depth indicates the true distance from the water surface to the bottom of the water vertically, also known as actual water depth. Relative water depth is the distance to the riverbed starting from the depth reference plane, which is commonly seen in waterway charts. When marking, if the water depth exceeds the reference plane, it is marked with a negative number; otherwise, it is represented by a positive number.

[0053] Absolute water depth will change with the fluctuation of water level and is the key factor to determine whether ships can pass through; while relative water depth is only affected by the change of riverbed, and because the river channel changes slowly, relative water depth can be used as a terrain reference and is stable. Definition:

[0054] Δh = water level base - depth base (1)

[0055] The absolute water depth calculation formula is:

[0056] D=W+D ρ +Δh (2)

[0057] Where D represents the absolute water depth, D ρ Indicates relative water depth, and W indicates measured water level value.

[0058] The weekly forecast maintenance water depth is D U , the water depth (relative water depth) shown below the water level W is D W , then the absolute water depth D of the navigable water depth area satisfies:

[0059] D≥D U (3)

[0060] Substituting into equation (2), since the water depth and water level of the Yangtze River channel use the same reference plane, Δh = 0, that is, the water depth D W satisfy:

[0061] D W ≥D U -W(4)

[0062] 2. Boundary point extraction

[0063] In order to obtain the river area that meets the specified water depth, it is necessary to accurately extract the boundary coordinate points of the river. The specific process is as follows:

[0064] 1) Obtain the illustrated water depth point set, establish the plane coordinate system OXY in the channel topographic mapping, and construct the Delaunay triangulation based on the illustrated water depth point set, store the adjacency relationship between triangle edges and vertices to establish the topological relationship. The original Delaunay triangulation result is as follows: Figure 3 shown.

[0065] 2) By Figure 3It can be seen that there are some triangles with too large side lengths in the original segmentation results. These triangles appear outside the river channel, which will have an adverse effect on subsequent analysis. Therefore, a triangle length threshold is set based on the maximum interval distance between adjacent water depth collection points. Through this threshold, those narrow and long erroneous triangles with too large areas can be effectively eliminated, thereby optimizing the segmentation results.

[0066] 3) Input the channel maintenance water depth D w , traverse the triangulation network, for any triangle ABC, if there is a water depth D at point A A >D w The water depth at point B is D B <D w , then there must be a point (X K ,Y K ), the actual water depth at that point is D K =D w Obviously, point K is the boundary point. By linear interpolation, the coordinates of the boundary point can be obtained:

[0067]

[0068] Draw the boundary point extraction results, such as Figure 4 shown.

[0069] 3. Extraction of waterway plane boundary

[0070] 1) Add boundary points to the original water depth dataset, reconstruct the Delaunay triangulation, and optimize the triangulation according to the triangle length threshold.

[0071] 2) Input the channel maintenance water depth D w For triangle ABC, if the water depths of the three vertices satisfy D ≥ D w , then it meets the screening criteria, and the area formed by the screened triangle set is the area M that meets the channel water depth.

[0072] 3) In order to divide M into closed polygonal areas, the following process is designed:

[0073] ① Count the number of times each edge of the triangle appears. Obviously, the edge with a number of appearances equal to 1 represents the boundary of the region, and the boundary is added to the boundary set B.

[0074] ② Get any edge L1 in the boundary set B and define its front and back endpoints as L 1a , L 1b , L 1a , L 1b Add to the closed area P1, if there is another edge L2 in the boundary set, so that L 1b is the common endpoint of the two edges, then add the non-common endpoint L of L22b Go to P1 and continue looking for the node with endpoint L 2b The edge L3 is obtained until there is no edge that meets the condition in the boundary set B. At this time, the first and last points of P1 are the same, that is, L nb =L 1a , the edges associated with the points in P1 form a closed polygon.

[0075] ③ Create a closed region P2, and search for common endpoints for the edges in the boundary set B that are not in P1 until all edges are classified. At this time, there is a closed region set: P = {P1, P2, ..., P n}.

[0076] 4) For any closed area P i , there may be an intersection point P i Divided into several small closed areas, the sub-areas do not support ship navigation, so they need to be split:

[0077] ①For any closed area P i , regardless of the case where the beginning and the end are the same, each point appears only once; therefore, removing the end point of the boundary set B, the points that appear more than once are the intersection points of the closed area, and the intersection point set N is constructed.

[0078] ② If the closed area P i If there is an intersection, then P i Further decomposition. Extract the area between the two occurrences of the same intersection to form a closed interval, and the remaining points to form a closed interval. Loop through each closed interval obtained by decomposition until there are no more intersections in any closed interval. The decomposition is completed, and all the closed intervals obtained by decomposition constitute the navigable water depth area of ​​the channel.

[0079] Therefore, for the largest closed polygon in the plane boundary of the channel, the holes can be eliminated through the above operations ① and ② to obtain the navigable water depth area of ​​the channel, such as Figure 5 shown.

[0080] In summary, within the plane boundary of the waterway, there is a closed area with the largest area, which is defined as P max .P max The interior may contain some cavities, which constitute the obstruction area P drop Therefore, the navigable area must be included in P max but exclude P drop Based on the results of the separation of the waterway plane boundary, human-computer interaction is introduced to assist the staff in effectively improving the accuracy of navigable area boundary extraction.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for separating waterway plane boundaries based on Delaunay triangulation, characterized by: Use the measured water level or predicted water level data to dynamically correct the water depth points in the waterway topographic map to obtain the actual water depth; After obtaining the actual water depth, the boundary points of the river channel are extracted to obtain the river channel area that meets the specified water depth, wherein the water depth point where the actual water depth is equal to the waterway maintenance water depth is taken as the boundary point, and a boundary point set is formed; Add the boundary point set to the original water depth data set, reconstruct the Delaunay triangulation, filter out all triangles whose actual water depth is greater than or equal to the waterway maintenance water depth, and obtain a set of triangular areas that meet the waterway maintenance water depth; Counting the number of occurrences of each edge of the triangle in the triangular region set, and adding the triangular edges representing the region boundaries into the boundary set; Find the edges in the boundary set that can form a closed area, and merge these edges into multiple closed polygons, that is, obtain the waterway plane boundary; Eliminate the remaining holes in the largest closed polygon in the plane boundary of the channel to obtain the navigable water depth area of ​​the channel.

2. The method for separating waterway plane boundaries according to claim 1, characterized in that: Methods for obtaining the actual water depth include: According to the calculation formula of actual water depth: D=W+D ρ +Δh Where D represents the actual water depth, D ρ represents the water depth shown in the figure, W represents the measured water level value, and Δh represents the difference between the water level reference plane and the depth reference plane; The weekly forecast maintenance water depth is D U , the water depth shown below the measured water level W is recorded as D W ; The actual water depth D in the navigable water depth area needs to satisfy D ≥ D U , then the water depth D under the measured water level W is obtained W Need to meet: D W ≥D U -W-Δh, thus achieving the water depth D shown in the figure W Dynamic correction of According to the corrected water depth D W Calculate the actual water depth D.

3. The method for separating waterway plane boundaries according to claim 1, characterized in that: The method of extracting boundary points includes: obtaining a set of illustrated water depth points in the waterway topographic map, establishing a plane coordinate system, and constructing a Delaunay triangulation network based on the illustrated water depth point set, storing the adjacency relationship between the edges and vertices of the triangle to establish a topological relationship; By setting a triangle length threshold, narrow and long triangles with too large area are eliminated; Set channel maintenance water depth D w For any triangle in the triangulation network, if any two vertices in the triangle satisfy: the water depth of one vertex is greater than D w , the water depth of the other vertex is less than D w ; Then there is a point K in the line segment between these two vertices, and the actual water depth D of point K K =D w , the point K is the boundary point; the coordinates of point K are calculated by linear interpolation; Traverse all triangles in the triangulated network and obtain the boundary points in the above manner to form a boundary point set.

4. The method for separating waterway plane boundaries according to claim 1, characterized in that: Adding the boundary point set to the original water depth data set, and reconstructing the Delaunay triangulation based on the original water depth data set; By setting a triangle length threshold, narrow and long triangles with too large area are eliminated to optimize the triangulated network; Set channel maintenance water depth D w If there is a triangle in the triangulation network, the water depths of the three vertices are greater than or equal to D w , then the triangle meets the screening requirements; Traverse the triangulated network and filter out all triangles that meet the screening requirements to form a triangular area set.

5. The method for separating waterway plane boundaries according to claim 1, characterized in that: The number of occurrences of all triangle edges in the triangle region set is counted, and the triangle edges with a number of occurrence of 1 are added to the boundary set.

6. The method for separating waterway plane boundaries according to claim 1, characterized in that: The method of finding the edge in the boundary set that can form a closed area includes: obtaining any edge L1 in the boundary set, and dividing its two end points L 1a , L 1b Add to a closed region set P1; if there is another edge L2 in the boundary set, and L1 and L2 have a common endpoint L 1b , then add the non-public endpoints in edge L2 to the closed area set P1; continue to search for edge L3 that has a common endpoint with edge L2, and add the non-public endpoints of edge L3 to the closed area set P1, and traverse all edges in the boundary set until there is no edge that meets the conditions in the boundary set. At this time, the first and last points in the closed area set P1 are the same, and the associated edges of the points in P1 form a closed polygon; Create a closed region set P2, find common endpoints for the remaining edges in the boundary set, and classify all edges in the above manner to obtain a closed region set P = {P1, P2, ..., P n }, that is, the plane boundary of the channel is obtained; the obstruction area within the largest closed polygon in the plane boundary of the channel is eliminated to obtain the navigable water depth area of ​​the channel.

7. The method for separating the waterway plane boundary according to claim 6, characterized in that: The method of removing the obstruction area within the largest closed polygon in the plane boundary of the channel to obtain the navigable water depth area range of the channel includes: for any closed area set P i If there is an intersection, P i Divided into several small closed areas, the sub-areas do not support ship navigation; regardless of the same head and tail, each point appears only once; therefore, the tail endpoint in the boundary set is removed, and the point that appears more than once is the intersection of the closed area; If there is an intersection within the maximum closed polygon, the area between the two occurrences of the same intersection is extracted to form a closed interval, and the remaining points constitute a closed interval; each closed interval is traversed in a loop until there is no intersection in any closed interval, that is, the navigable water depth area of ​​the channel is separated.

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