An automatic lake grid division method

Abstract

The present invention discloses a method for automatically dividing lake grids, which includes: dividing the lake waters step by step according to administrative regions until reaching the county level; evenly dividing the lake areas at the county level using square grids; merging the irregular grids generated at the lake boundaries after division, and if there are lake center islands, merging the irregular grids around the lake center islands; and encoding the merged grids. By dividing the classified lake waters with square grids, the present invention obtains two types of grids, regular and irregular. The irregular grids are abstracted into graphs. Considering both the lake boundaries and the lake center island areas, the idea of depth-first search is adopted for merging and adjustment to achieve computer automatic division, which can improve the rationality, flexibility and efficiency of the method for automatically dividing lake grids.

Description

Technical Field

[0001] The present invention relates to the field of lake management, and particularly to a method for automatically dividing lake grids. Background Art

[0002] The division of lake grids is beneficial to the inspection and management of lakes. Compared with the division of land grids, the division of water area grids has its particularity and needs to follow certain division principles. There are many reference bases for land grid division. For example, the city is divided into grids with roads as grid lines; the land is divided into grids according to vegetation types; the land is divided into grids according to land uses, etc. However, there are few reference bases for water area division and the division is difficult. Usually, the division principles are determined starting from the division purpose. The influencing factors for grid division are mainly factors such as administrative divisions, lake morphology, and area within the lake management scope.

[0003] Scientific division of lake grids generally needs to follow the following principles: hierarchical principle, territorial integrity principle, in-territory rule principle, and integrity principle. Currently, the methods for dividing lake area grids generally target grid division in a small area range, mainly including the regular grid method, administrative division method, and manual division method.

[0004] The regular grid method divides the lake area into regularly arranged grid units with the same size. This division method is simple and easy for spatial analysis. However, since the lake boundary line is an irregular curve and there are many islands inside many lakes, the regular grid cannot handle this situation. In addition, due to the different complexities of lake bays and river branches and the different distributions of open water areas and polder areas in different lakes, the regular grid division method cannot make a reasonable division.

[0005] Administrative division divides lake grids according to the scope of administrative divisions, and divides them level by level according to province - city - county - township (town) - village. Each level is responsible for the corresponding grid and arranges corresponding inspection personnel. The grid levels of this division method are clear, which is beneficial to hierarchical management and grid coding. However, the flexibility of the grids after division is not high, and the divided lake areas are uneven.

[0006] Manual division is the most widely used method for dividing lake grids at present. After selecting the division area of the lake, the lake area is manually divided into networks with equivalent areas according to the lake morphology, water area area, etc. This division method has high flexibility and can divide grids according to the characteristics of each lake. However, the grid coding is complex and the efficiency of constructing grids is relatively low. Summary of the Invention

[0007] Objective of the Invention: Aiming at the above problems, the objective of the present invention is to provide a method for automatically dividing lake grids. By dividing the classified lake waters with square grids, two types of grids, regular and irregular, are obtained. The irregular grids are abstracted into graphs. Considering both the lake boundary and the central island areas, the idea of depth-first search is adopted for merging and adjustment to achieve computer automatic division, which can improve the rationality, flexibility, and efficiency of the method for automatically dividing lake grids.

[0008] Technical Solution: A method for automatically dividing lake grids of the present invention includes: dividing the lake waters step by step according to administrative regions until the county level; evenly dividing the lake areas at the county level with square grids; merging the irregular grids generated by the lake boundary after division. If there is a central island, merging the irregular grids around the central island; encoding the merged grids.

[0009] Among them, the merging of the lake boundary grids adopts the four-direction adjacent rule combined with the depth-first search method.

[0010] Furthermore, the merging of the lake boundary grids adopting the four-direction adjacent rule combined with the depth-first search method includes:

[0011] S101, setting the relationship between the area S' of the irregular grid of the lake boundary and the area S of the regular grid as: S'∈[0.5S,1.5S], establishing the relationship between each grid: assuming that any irregular grid has a connection relationship with the grids in its upper, lower, left, and right directions, abstracting the grid into an undirected graph, where the vertices of the undirected graph represent the grids and the edges represent the connection relationships between the grids;

[0012] S102, randomly selecting a grid v in the irregular grid as the starting grid, calculating the area of the current grid v, and setting the access as true;

[0013] S103, finding the unvisited grid v' among all the adjacent grids of the current grid v, calculating the area of the grid v'. If the area of the current grid v belongs to the range of [0.5S,1.5S], then the grid v and v' are not merged, and the grid v' is used as the current grid to continue visiting the adjacent grids; otherwise, the grid v and v' are merged, and the merged new grid is used as the current grid to continue visiting the adjacent grids;

[0014] S104, if all the adjacent grids of the current grid have been visited, then take a step back and use the previous grid as the current grid for exploration;

[0015] S105, repeating steps S103 - S104 until all the adjacent grids of the starting grid have been visited, then the merging ends.

[0016] Furthermore, the merging rule for the irregular grids around the central island is:

[0017] S201, taking the area nS as the demarcation point, divide the lake center island into a large island and a small island. The area of the large island S” > nS, and the merging rule is the same as the merging rule for irregular grids of the lake boundary, where n is a coefficient;

[0018] S202, the area of the small island S” ∈ (0, nS]. If the lake center island is within a single grid, it has no impact on the grid;

[0019] If the lake center island straddles two grids, use the four-direction adjacent rule to merge the two grids;

[0020] If the lake center island straddles four grids and none of the four grids meet the balance requirement, use the eight-direction adjacent rule to merge the four grids.

[0021] Furthermore, the rule for uniformly dividing the lake area at the county level using regular grids is as follows:

[0022] Divide the lake into four levels according to the water area of 5 km 2 、50 km 2 、400 km 2 The three demarcation points. The side lengths of the corresponding divided grid for each level are 0.5 km, 1 km, 1.5 km, and 2 km respectively.

[0023] Beneficial effects: Compared with the prior art, the remarkable advantages of the present invention are as follows: By combining the existing lake grid division method, the basic principles of lake division are established. First, hierarchical division is carried out through administrative regions and then merged, realizing the computer automatic division of lake grids, effectively improving the efficiency of lake grid division; During the merging process, the grids are abstracted into graphs, and either four-direction adjacent or eight-direction adjacent can be selected, improving the flexibility of the merging process; Through the method of the present invention, lakes of various shapes can be quickly divided, and finally the sizes and shapes of the obtained grids are quite similar and there are no topological errors; Due to the high efficiency of this method, the same lake can be divided using grids of different sizes to obtain multiple division results, and finally the optimal division result can be selected by comparison. Brief Description of the Drawings

[0024] Figure 1 It is the flow chart of the present invention;

[0025] Figure 2 It is the schematic diagram of the grid grading of the lake area;

[0026] Figure 3 It is the result after dividing the lake area at the county level using regular grids;

[0027] Figure 4 It is the schematic diagram of abstracting the grid into a graph;

[0028] Figure 5The result after the merger of irregular grids for the lake boundary;

[0029] Figure 6 The result after the merger of irregular grids around small islands;

[0030] Figure 7 The result after the merger of irregular grids around large islands;

[0031] Figure 8 For the grid coding style;

[0032] Figure 9 For the division results of the Taihu Lake area under different grid side lengths, as well as the division results of the Taihu Lake area on the grid-based management information platform for lakes under the jurisdiction of Jiangsu Province. Specific implementation manners

[0033] In order to make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] As Figure 1 shown in the flowchart, a method for automatically dividing lake grids according to this embodiment includes: dividing the lake waters step by step according to administrative regions until the county level; uniformly dividing the lake areas at the county level using square grids; merging the irregular grids generated by the lake boundaries after division, and if there are lake center islands, merging the irregular grids around the lake center islands; coding the merged grids; wherein the merger of lake boundary grids adopts the four-direction adjacent rule combined with the depth-first search method.

[0035] In this embodiment, the lake areas are classified according to administrative divisions. For lakes that are vast in area and span provinces, cities and counties, they are first divided step by step according to province-city-county (district), and the last-level grids are divided on the basis of county (district), as Figure 2 shown. The first-level grid is a polygon area composed of all the waters of the lake, and the second, third, and fourth-level grids are grids divided by the administrative division boundaries of provinces, cities, and counties (districts) respectively.

[0036] On the basis of the fourth-level grid, the fifth-level grid uniformly divides the lake areas at the county (district) level using regular grids. For different lakes, the grid size mainly refers to the water area of the lake. The lakes are divided into four levels according to the three demarcation points of the water area of 5 km 2 , 50 km 2 , 400 km 2 , and the corresponding grid side lengths for each level of division are 0.5 km, 1 km, 1.5 km, and 2 km respectively, as shown in Table 1.

[0037] Table 1 Relationship between lake area and grid side length

[0038] Area Side length <![CDATA[0 to 5 km 2 > 0.5 km <![CDATA[5 - 50 km 2 > 1 km <![CDATA[50~400km 2 > 1.5 km <![CDATA[400km 2 or more]]> 2 km

[0039] Grid division is to divide the lake area at the county (district) level. The area for managing the lake is generally larger than the water area. Therefore, a certain distance is set between the left and lower boundaries of the grid and the left and lower boundaries of the lake. For example, Figure 3 As shown, the distance is a meters, and the value of a is the average value of the difference in the shoreline distances between the high-water period and the low-water period of the lake. The lake water area is divided into regular units with the same area and irregular units with different areas. The lake area inside is divided into regular square grids. The shaded part is the irregular grid generated by the boundary division, and the area sizes vary.

[0040] In order to meet the principle of territorial regularity, it is necessary to merge the irregular grids to ensure that the areas of all grids are balanced. The depth-first search method can traverse all vertices in a connected graph. To ensure that all irregular grids are merged, the depth-first search algorithm is used to merge the irregular grids while traversing them. The merging of irregular grids at the lake boundary using the four-direction adjacent rule combined with the depth-first search method includes:

[0041] S101, stipulate the relationship between the area S' of the irregular grid at the lake boundary and the area S of the regular grid as: S'∈[0.5S,1.5S], and establish the relationship between each grid: Assume that there is a connection relationship between any irregular grid and the grids in its upper, lower, left, and right directions. Abstract the grid into an undirected graph, where the vertices of the undirected graph represent the grids and the edges represent the connection relationships between the grids. The abstract schematic diagram is as Figure 4 shown.

[0042] S102, randomly select a grid v in the irregular grid as the starting grid, calculate the area of the current grid v, and set the access to true;

[0043] S103, find the unvisited grid v' among all adjacent grids of the current grid v, calculate the area of the grid v'. If the area of the current grid v belongs to the range of [0.5S,1.5S], then the grid v and v' are not merged, and continue to visit the adjacent grids with the grid v' as the current grid; otherwise, the grid v and v’ are merged, and the merged new grid is used as the current grid to continue visiting the adjacent grids;

[0044] S104, if all adjacent grids of the current grid have been visited, then take a step back and use the previous grid as the current grid for exploration;

[0045] S105, repeat steps S103 - S104 until all adjacent grids of the starting grid have been visited, then end the merging.

[0046] The result after merging the irregular grids at the lake boundary is as Figure 5As shown, it can be seen from the merging results that the area difference between the irregular grid and the regular grid is relatively small, meeting the principle of regular grids within the jurisdiction.

[0047] Lake islands usually span multiple grids and vary in size. To meet the integrity principle, grid merging is required. Different merging rules apply to different islands. The merging rule for the irregular grids around the lake island is as follows:

[0048] S201. Taking the area nS as the demarcation point, the lake island is divided into large islands and small islands. The area of the large island S” > nS, and the merging rule is the same as that for the irregular grids at the lake boundary. n is a coefficient.

[0049] S202. The area of the small island S” ∈ (0, nS]. If the lake island is within a single grid, it has no impact on the grid.

[0050] If the lake island spans two grids, the two grids are merged using the four-direction adjacent rule.

[0051] If the lake island spans four grids and none of the four grids meet the balance requirement, the four grids are merged using the eight-direction adjacent rule.

[0052] The rule for evenly dividing the lake area at the county level using regular grids is as follows:

[0053] As Figure 6 Shown are the four lake islands 1, 2, 3, and 4 with an area S” ∈ (0, nS]. Lake island 1 is within a single grid and has no impact on the grid. Lake island 2 spans two grids, and the two grids are merged using the four-direction adjacent rule. Lake island 3 spans four grids, and the four grids are merged using the eight-direction adjacent rule. The area of lake island 4 is very small, and the areas of the four grids around it all meet the balance requirement, so no grid merging is needed.

[0054] If the area of the lake island S” > nS, there are many irregular grids along the shore of such an island, and merging processing is required. The merging method refers to the merging of the grids at the lake boundary. The only difference from the lake boundary situation is that the irregular grids generated by the lake island surround the lake island on the outside. Figure 7 What is shown is the result before and after the merging of the irregular grids around a large island. The irregular grids outside the lake island shown in a are merged to obtain the result shown in b.

[0055] Compared with manual division, computer automatic division can efficiently encode the grids. The encoding of each grid is unique and rigorous. In this embodiment, referring to the urban grid encoding principle, the lake grid encoding is carried out in accordance with the "Rules for the Division and Coding of Unit Grids in the Urban Municipal Comprehensive Supervision Information System" of the urban construction industry standard of the People's Republic of China. The total encoding is nine digits. The first six digits are the administrative division codes of the county (district) and above, which are implemented in accordance with the GB / T2260 standard. The last three digits are the sequence codes of the last-level grids from top to bottom and from left to right. The encoding style is as Figure 8 shown.

[0056] Using the grid automatic division method described in this embodiment to automatically divide the Taihu Lake waters, the grid side lengths are respectively selected as 1.5 km, 2 km and 2.5 km, corresponding to Figure 9 a, b and c in. d is the manual division result of the Taihu Lake waters in the grid-based management information platform for lakes under the jurisdiction of Jiangsu Province. In the obtained division result map, the lake is divided into seven waters by the administrative division lines at the county (district) level. All grids cover all the waters of the lake, meeting the division grading principle, territorial integrity principle, territorial internal rule principle, and integrity principle.

[0057] Compared with manual division, the grids of automatic division are more regular, the encoding speed is fast, and the efficiency of lake grid division is improved. It can be seen from the three schemes selected in the present invention that if the grid side length is too small, the shape of the grids in the boundary area is complex after merging, increasing the difficulty of lake inspection and management. If the grid side length is too large, the task volume of each lake inspector will increase. With the high division efficiency, the present invention can arbitrarily adjust the grid side length, conduct comparative analysis, and find the optimal division scheme.

Claims

1. An automatic lake grid division method, characterized in that, it includes: Gradually divide the lake waters according to administrative regions until the county level; use square grids to evenly divide the lake areas at the county level; Merge the irregular grids generated by the lake boundaries after division. If there is a lake center island, merge the irregular grids around the lake center island; encode the merged grids; Among them, the lake boundary grid merging adopts the four-direction adjacent rule combined with the depth-first search method; The lake boundary grid merging adopting the four-direction adjacent rule combined with the depth-first search method includes: S101, Set the relationship between the area S' of the irregular grid of the lake boundary and the area S of the regular grid as: S' ∈ [0.5S, 1.5S], and establish the relationship between each grid: Assume that any irregular grid has a connection relationship with the grids in its upper, lower, left, and right directions. Abstract the grid into an undirected graph, where the vertices of the undirected graph represent the grids and the edges represent the connection relationships between the grids; S102, Arbitrarily select a grid v in the irregular grid as the starting grid, and calculate the area of the current grid v; S103, Find the unvisited grid v' among all the adjacent grids of the current grid v, and calculate the area of the grid v'. If the area of the current grid v belongs to the range of [0.5S, 1.5S], then the grids v and v' are not merged, and continue to visit the adjacent grids with the grid v' as the current grid; otherwise, merge the grids v and v', and continue to visit the adjacent grids with the merged new grid as the current grid; S104, If all the adjacent grids of the current grid have been visited, take a step back and use the grid in the previous step as the current grid for exploration; S105, Repeat steps S103 - S104 until all the adjacent grids of the starting grid have been visited, then end the merging; The merging rule for the irregular grids around the lake center island is: S201, Take the area nS as the demarcation point to divide the lake center island into large islands and small islands. The area of the large island S” > nS, and the merging rule is the same as the merging rule for the irregular grids of the lake boundary, where n is a coefficient; S202, The area of the small island S” ∈ (0, nS]. If the lake center island is within a single grid, it has no impact on the grid; If the lake center island straddles two grids, merge the two grids using the four-direction adjacent rule; If the lake center island straddles four grids and none of the four grids meet the balance requirement, merge the four grids using the eight-direction adjacent rule; The rule for evenly dividing the lake areas at the county level using regular grids is: The lakes are divided into four levels according to three demarcation points of water area of 5 km 2 , 50 km 2 , 400 km 2 . The side lengths of the division grids corresponding to each level are 0.5 km, 1 km, 1.5 km, and 2 km respectively.

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