A nested partitioning method for inland flow basins based on set concept

Abstract

The present invention discloses a nested division method of inland flow basins based on the concept of set, which relates to the technical field of hydrological basin division. The method comprises the following steps: extracting the scope of inland flow basins based on a digital elevation model; merging adjacent inland flow basins to construct an inland flow basin set, encoding the inland flow basin set with the largest area and performing nested division until the number of inland flow basins at each level is less than or equal to 10; dividing the outland flow basins and encoding them, and then merging the uncoded inland flow basins to the adjacent coded basins based on the lowest point of the boundary; for a single inland flow basin with an area greater than a threshold, the Pfafstetter method is used to process the inland flow basin to perform secondary basin division. The present invention combines spatially adjacent inland flow basins and performs nested division, which facilitates the decomposition of secondary basins, and allocates codes according to the basin area when dividing the secondary basins, so that the inland flow basins with large areas are encoded first, and the division results are more reasonable.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrological watershed division, and in particular to a method for nested division of inland flow watersheds based on a set concept. Background Art

[0002] In the context of discussing water resources management and ecological protection, the importance of understanding and managing inland basins cannot be ignored. In the existing division of hydrological basins, the water flow in the basin that can directly or indirectly flow into the ocean is called an external basin, and the water flow that eventually flows into inland lakes or disappears in the desert is called an inland basin. Water resources in inland basins are relatively scarce, and the supply of water resources has an important impact on the ecosystem and human life in the surrounding areas; therefore, studying the hydrological process, water resources management, and protection and restoration of inland wetlands in inland basins is of great significance to maintaining the balance and sustainable development of inland ecosystems. Among them, accurately dividing and extracting the scope of inland basins is an important basis for basin water resources management and scientific decision-making.

[0003] The existing methods for dividing inland drainage basins often only encode the largest inland drainage basin in the study area, and directly merge other uncoded inland drainage basins into other coded basins. In areas where inland drainage basins are concentrated, this method will cause many important inland drainage basins to not be individually coded, and the division results are unreasonable. To address this problem, some researchers have tried to manually code each inland drainage basin, but this manual processing method is time-consuming and has poor reproducibility.

[0004] Therefore, a new method for inland flow basin division is urgently needed, which can realize automatic and reasonable basin nesting division in the concentrated area of ​​inland flow basin based on the set idea, so as to solve the problem of unreasonable coding in the concentrated distribution area of ​​inland flow basin in the existing basin division method.

[0005] Currently, no effective solution has been proposed for the problems in the related technologies. Summary of the invention

[0006] In response to the problems in the related technology, the present invention proposes a nested division method of inland flow basins based on the set idea, which has the advantages of combining spatially adjacent inland flow basins into a whole for encoding based on the set idea, and realizing automatic and reasonable nested division of basins in concentrated areas of inland flow basins, thereby solving the problem in the prior art that in areas with concentrated distribution of inland flow basins, many important inland flow basins cannot be individually encoded and the division results are unreasonable.

[0007] To this end, the specific technical solution adopted by the present invention is as follows:

[0008] A method for nested division of inland flow basins based on set thinking, the method comprising the following steps:

[0009] S1. Extract the internal flow basin range based on the digital elevation model;

[0010] S2. Merge adjacent internal flow basins to construct an internal flow basin set, encode the internal flow basin set with the largest area, and nest and divide it until the number of internal flow basins at each level is less than or equal to 10;

[0011] S3, divide the outflow basin and encode it, and then merge the uncoded inflow basin into the adjacent coded basin based on the lowest point of the boundary;

[0012] S4. For a single internal flow basin whose area is larger than the threshold, the Pfafstetter method is used to process the internal flow basin to perform secondary watershed division until the area of ​​the secondary internal flow basin is less than or equal to the threshold.

[0013] Furthermore, based on the digital elevation model, extracting the internal flow basin range includes the following steps:

[0014] S11. Based on the digital elevation model, the single flow direction algorithm is used to calculate the flow direction and the cumulative amount of confluence, and the river network is extracted according to the preset threshold;

[0015] S12. Based on the extracted river network, mark the rivers whose end points are located on land and have no downstream as inland rivers, and mark the upstream catchment areas of inland rivers as endorheic basins, and mark the upstream catchment areas of non-inland rivers as endorheic basins.

[0016] Further, adjacent inland watersheds are merged to construct an inland watershed set, and the inland watershed set with the largest area is encoded and nested until the number of inland watersheds at each level is less than or equal to 10, including the following steps:

[0017] S21, extracting the scope and boundary of each inland flow basin, and traversing the adjacent basins of each inland flow basin;

[0018] S22, merging adjacent inland flow basins according to the traversal results to obtain an inland flow basin set, and establishing an unprocessed basin set list, and adding the inland flow basin set with the largest area to the unprocessed basin set list;

[0019] S23, calculating the area of ​​the inland flow basin set in the unprocessed basin set list, determining the expected number and expected area of ​​the secondary basin divisions, and constructing the key inland flow basin set;

[0020] S24. According to the nested division rule, secondary watershed division coding is performed on the key inland flow watershed set based on the calculation results.

[0021] Further, calculating the area of ​​the inland flow basin set in the unprocessed basin set list, determining the expected number and expected area of ​​the secondary basin divisions, and constructing the key inland flow basin set includes the following steps:

[0022] S231, calculating the total area of ​​the inland flow basin sets and the area of ​​each inland flow basin set in the unprocessed basin set list;

[0023] S232. Calculate the expected number of sub-basins and their expected areas according to the area ratio;

[0024] S233. Select the set of inland watersheds with the largest area and construct a set of key inland watersheds.

[0025] Further, according to the nested division rule, the secondary watershed division coding of the key inland watershed set based on the calculation results includes the following steps:

[0026] S241. Based on the set of key inland flow basins, select the inland flow basin with the largest area to construct the key inland flow basins;

[0027] S242. Based on the key inland flow basins, construct a sub-basin set and encode the sub-basin set separately;

[0028] S243, according to the neighboring relationship, merge the uncoded inland flow basins into a new basin set, add it to the unprocessed basin set list, and update the expected number of sub-basin divisions;

[0029] S244, repeating steps S241 to S243 until the expected number of sub-basins to be divided is 0;

[0030] S245. If the unprocessed watershed set list is not empty, the unprocessed inland watersheds in the unprocessed watershed set list are merged into adjacent coded watersheds through the lowest point on the watershed boundary, and the division is stopped.

[0031] Furthermore, based on the key inland flow basins, a sub-basin set is constructed, and the sub-basin set is individually coded, including the following steps:

[0032] S2421. If the area of ​​the key inland flow basin is greater than or equal to the expected area, the key inland flow basin is taken as a new set; otherwise, the adjacent basins are merged based on the adjacent relationship with the key inland flow basin as a seed;

[0033] S2422. Based on the merging result of adjacent watersheds, a sub-watershed set is constructed, and the area of ​​the sub-watershed set is calculated;

[0034] S2423. Repeat steps S2421 and S2422 until the area of ​​the sub-basin set meets the expected area.

[0035] Furthermore, dividing the outflow basin and coding it, and then merging the uncoded inflow basin to the adjacent coded basin based on the lowest point of the boundary includes the following steps:

[0036] S31. Use the Pfafstetter watershed coding algorithm to divide and code coastal watersheds;

[0037] S32, divide and code general watersheds;

[0038] S33. Based on the lowest point of the boundary of the uncoded watershed set, merge the uncoded watershed into the adjacent coded watershed.

[0039] Furthermore, dividing the general watershed and coding it includes the following steps:

[0040] S321, based on the general outflow basin, trace back along the main stream from the basin outlet to the river source;

[0041] S322. Compare the size of the upstream drainage area at the confluence of the river during the tracing process to determine the main stream and tributaries;

[0042] S323, based on the determined tributaries, select and encode several tributaries with the largest catchment areas, and divide the general river basin into several intermediate general river basins according to the encoded tributaries, and encode the intermediate general river basins;

[0043] S324. Based on the lowest elevation point on the watershed boundary, merge the uncoded inland flow watershed into the adjacent coded watershed.

[0044] Further, based on the lowest point of the boundary of the uncoded watershed set, merging the uncoded watershed into the adjacent coded watershed includes the following steps:

[0045] S331, traverse the boundary pixels of the uncoded watershed set;

[0046] S332, based on the traversal result, determining the pixel position where the minimum elevation value is located;

[0047] S333. Based on the pixel position where the minimum elevation value is located, merge the uncoded watershed set into the nearest coded watershed in a clockwise direction.

[0048] Further, for a single inland flow basin whose area is larger than the threshold, the Pfafstetter method is used to process the inland flow basin to divide the secondary watershed until the area of ​​the secondary inland flow basin is less than or equal to the threshold, including the following steps:

[0049] S41. Trace back from the end of the river to the source of the river. When you encounter a river intersection, take the one with a larger upstream area as the main stream and the one with a smaller upstream area as the tributary. Record the location of the tributary and continue tracing upstream along the main stream until you reach the source of the river.

[0050] S42. Among all the recorded tributaries, select the four tributaries with the largest catchment areas as tributary basins, and code the tributary basins as 2, 4, 6, and 8 in order from near to far from the river terminal;

[0051] S43, based on the tributary basins, the original basin is divided into five intermediate basins, and the intermediate basins are coded as 1, 3, 5, 7, and 9 in order from near to far from the river terminal;

[0052] S44. Compare the secondary internal flow basin area with the threshold. If the secondary internal flow basin area is larger than the threshold, repeat steps S41 to S43 until the secondary internal flow basin area is smaller than or equal to the threshold.

[0053] The beneficial effects of the present invention are:

[0054] (1) The present invention solves the problem that the existing internal flow basin division method often only encodes the largest internal flow basin in the study area, and merges other uncoded internal flow basins into other coded basins, resulting in many important internal flow basins in the concentrated distribution area of ​​internal flow basins cannot be individually coded, and the division result is unreasonable; at the same time, the present invention combines spatially adjacent internal flow basins into a whole for coding, which can save the number of codes on the one hand, and facilitate the decomposition of secondary basins on the other hand; in addition, the present invention can allocate codes according to the basin area when dividing the secondary basin, so that the key internal flow basins with large areas are coded first, and the division result is more reasonable.

[0055] (2) Compared with existing methods, the present invention can be applied to areas with a large number of inland watersheds. It can automatically perform nested divisions on the inland watersheds to obtain multiple levels of inland watershed boundaries. It has broader application prospects in terrain analysis, watershed simulation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0057] Figure 1 It is a flowchart of a method for nested division of inland flow basins based on a set concept according to an embodiment of the present invention;

[0058] Figure 2 This is one of the specific implementation diagrams of a method for nesting internal flow basins based on a set concept according to an embodiment of the present invention;

[0059] Figure 3 This is a second specific implementation diagram of a method for nesting and dividing an inland flow basin based on a set concept according to an embodiment of the present invention;

[0060] Figure 4 It is a schematic diagram of the inland flow basin set decomposition process of an inland flow basin nested partitioning method based on the set concept according to an embodiment of the present invention.

[0061] Figure 5 It is a nested division result of an inland flow basin in a certain place according to an inland flow basin nested division method based on set concept according to an embodiment of the present invention. DETAILED DESCRIPTION

[0062] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention and are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, ordinary technicians in the field should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0063] According to an embodiment of the present invention, a method for nested partitioning of inland flow basins based on a set concept is provided.

[0064] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. Figure 1-Figure 3 As shown, Figure 2 The arrow ① in Figure 3 According to an embodiment of the present invention, a method for nested division of inland flow basins based on a set concept is provided. The method for nested division of inland flow basins based on a set concept comprises the following steps:

[0065] S1. Extract the internal flow basin range based on the digital elevation model;

[0066] S2. Merge adjacent internal flow basins to construct an internal flow basin set, encode the internal flow basin set with the largest area, and nest and divide it until the number of internal flow basins at each level is less than or equal to 10;

[0067] S3, divide the outflow basin and encode it, and then merge the uncoded inflow basin into the adjacent coded basin based on the lowest point of the boundary;

[0068] S4. For a single internal flow basin whose area is larger than the threshold, the Pfafstetter method is used to process the internal flow basin to perform secondary watershed division until the area of ​​the secondary internal flow basin is less than or equal to the threshold.

[0069] Specifically, the Pfafstetter coding method is a geographic coding method used to describe river systems. It can hierarchically encode river basins and their sub-basins through a systematic numbering rule, which is convenient for river basin data management and analysis. Pfafstetter coding is particularly suitable for focusing on the hydrological structure and hierarchical relationships of river basins, making the relationships within the basin and between adjacent basins clearly visible.

[0070] Specifically, for a watershed set to be divided that contains an inland drainage area, the range and boundary of a single inland drainage basin are extracted based on the flow direction data and depressions extracted from the digital elevation model. If there are two or more inland drainage basins and external drainage basins at the current watershed level, first, the adjacent inland drainage basins are merged into an inland drainage basin set and coded separately. Subsequently, the remaining external drainage basins are divided into secondary drainage basins according to the Pfafstetter coding method. Finally, the uncoded inland drainage basins are merged into the coded drainage basins. At this time, the secondary inland drainage basin types obtained may include separate inland drainage basins and inland drainage basin sets.

[0071] Specifically, for the inland flow basin set, assuming that for a given initial inland flow basin set A, it is desired to divide it into N subsets with relatively close areas and add them to the unprocessed set list.

[0072] Specifically, the inland flow basin set to be divided is added to the unprocessed set list (at this time, there is only one inland flow basin set in the unprocessed inland flow basin set list).

[0073] Specifically, calculate the total area S of the inland flow basin set in the current unprocessed set list. all , take the set R1 with the largest area, whose corresponding area is S1, and calculate the number of sub-basins that R1 can be divided into according to the area ratio n=Round(N×S1 / S all ), then in the current level basin, the expected area of ​​the secondary basin divided by R1 is S t = S1 / n; select the largest internal flow basin from the set R1, if the area of ​​the largest internal flow basin is not less than S t , it is directly used as a new set R2. Otherwise, it is used as a seed to continuously merge other adjacent basins to form a new set R2 until the area S2 of R2 is equal to the expected area S tclosest; encode set R2 separately, and analyze the difference set R1-R2 between set R1 and set R2, count the unconnected sets (there may be multiple) composed of the remaining uncoded inland flow basins, add them to the unprocessed set list, and update the number of subsets that have not been divided and coded N=N-1; if N is greater than 0, repeat the above steps until N=0, and finally, if the unprocessed list is not empty, merge those unprocessed inland flow basins into the adjacent coded basins through the lowest point on the basin boundary, and stop dividing.

[0074] Specifically, through the nested division of the internal flow basins, the internal flow basin set is decomposed into separate internal flow basins, which are divided using Pfafstetter coding until the area of ​​the divided secondary basin is smaller than the user-specified threshold, and the division is stopped.

[0075] In one embodiment, based on the digital elevation model, extracting the internal flow basin range includes the following steps:

[0076] S11. Based on the digital elevation model, the single flow direction algorithm is used to calculate the flow direction and the cumulative amount of confluence, and the river network is extracted according to the preset threshold;

[0077] S12. Based on the extracted river network, mark the rivers whose end points are located on land and have no downstream as inland rivers, and mark the upstream catchment areas of inland rivers as endorheic basins, and mark the upstream catchment areas of non-inland rivers as endorheic basins.

[0078] Specifically, the Digital Elevation Model (DEM) is a high-quality digital elevation model specifically used for hydrological and environmental research. It is an improvement on the global DEM data, which improves the accuracy and practicality of the model by removing systematic errors and non-water body errors.

[0079] Specifically, the single flow direction algorithm in this embodiment adopts the D8 algorithm. The characteristic of the single flow direction algorithm is that it simplifies the calculation process of the flow direction, making the simulation of the water flow path more intuitive and easy to understand. The D8 algorithm is a typical algorithm in the single flow direction algorithm. Its main advantage is that the calculation is simple and fast, and it can help identify a sufficiently large watershed, and then identify and map the main river network.

[0080] Specifically, in this embodiment, MERIT Hydro DEM data is first used as input data, and then the D8 algorithm is used to calculate the flow direction and confluence accumulation data, and 30 square kilometers is used as the threshold to extract the river network, and the rivers whose end points are located on land and have no downstream are marked as inland rivers, and the upstream of the river is traced back and marked as the inland basin, and the upstream catchment area of ​​the remaining rivers is marked as the external basin.

[0081] In one embodiment, merging adjacent inland watersheds to construct an inland watershed set, encoding the inland watershed set with the largest area and performing nested division until the number of inland watersheds at each level is less than or equal to 10 includes the following steps:

[0082] S21, extracting the scope and boundary of each inland flow basin, and traversing the adjacent basins of each inland flow basin;

[0083] S22, merging adjacent inland flow basins according to the traversal results to obtain an inland flow basin set, and establishing an unprocessed basin set list, and adding the inland flow basin set with the largest area to the unprocessed basin set list;

[0084] S23, calculating the area of ​​the inland flow basin set in the unprocessed basin set list, determining the expected number and expected area of ​​the secondary basin divisions, and constructing the key inland flow basin set;

[0085] S24. According to the nested division rule, secondary watershed division coding is performed on the key inland flow watershed set based on the calculation results.

[0086] Specifically, if there are multiple internal flow basins that are adjacent in space, they are combined into an internal flow basin set, which are treated as a whole when dividing the basin, and the largest internal flow basin set is coded as 9; the division and coding of the external flow areas in the region are carried out by using the Pfafstetter method to deal with general basins or coastal basins; the uncoded internal flow basin set is merged into the adjacent coded basin through the lowest point on the basin boundary. For the initial data, the largest internal flow basin set (coded as 9 in this embodiment) is marked when it is divided for the first time. When using Pfafstetter coding for nested division, a maximum of 10 secondary basins are divided at each level. When performing nested division of internal flow basins in this method, a division threshold can be specified, which defaults to 10.

[0087] Specifically, adjacent internal flow basins are combined into a basin set, and the area of ​​each set is calculated. The internal flow basin set with the largest area (key internal flow basin set) is initially encoded, and in this embodiment, the value is assigned to "9". Subsequently, the external flow basin is divided using the Pfafsftetter encoding method. Finally, the boundary pixels of the uncoded internal flow basin set are traversed to obtain the pixel position of the minimum elevation value, and the internal flow basin set is merged clockwise to the nearest coded basin.

[0088] Specifically, the largest inland flow basin set (coded as 9 in this embodiment) is added to the unprocessed set list, and is divided into N (10 by default) subsets with relatively close areas.

[0089] In one embodiment, calculating the area of ​​the inland flow basin set in the unprocessed watershed set list, determining the expected number and expected area of ​​the secondary watershed divisions, and constructing the key inland flow basin set includes the following steps:

[0090] S231, calculating the total area of ​​the inland flow basin sets and the area of ​​each inland flow basin set in the unprocessed basin set list;

[0091] S232. Calculate the expected number of sub-basins and their expected areas according to the area ratio;

[0092] S233. Select the set of inland watersheds with the largest area and construct a set of key inland watersheds.

[0093] Specifically, the formula for calculating the expected number of sub-basin divisions is:

[0094] n = Round ( N * S 1 / Sa 11 );

[0095] The formula for calculating the expected area of ​​a secondary watershed is:

[0096] S t = S 1 / n ;

[0097] In the formula, n represents the expected number of sub-basin divisions;

[0098] N Indicates the number of subsets that have not yet been divided into codes;

[0099] S 1 represents the area of ​​the largest inland flow basin set in the current unprocessed set list;

[0100] S a11 It represents the total area of ​​the inland flow basin set in the current unprocessed set list;

[0101] S t Indicates the expected area of ​​the divided secondary watershed.

[0102] In one embodiment, according to the nested partitioning rule, performing secondary basin partitioning encoding on the key inland flow basin set based on the calculation results includes the following steps:

[0103] S241. Based on the set of key inland flow basins, select the inland flow basin with the largest area to construct the key inland flow basins;

[0104] S242. Based on the key inland flow basins, construct a sub-basin set and encode the sub-basin set separately;

[0105] S243, according to the neighboring relationship, merge the uncoded inland flow basins into a new basin set, add it to the unprocessed basin set list, and update the expected number of sub-basin divisions;

[0106] S244, repeating steps S241 to S243 until the expected number of sub-basins to be divided is 0;

[0107] S245. If the unprocessed watershed set list is not empty, the unprocessed inland watersheds in the unprocessed watershed set list are merged into adjacent coded watersheds through the lowest point on the watershed boundary, and the division is stopped.

[0108] Specifically, calculate the total area S of the inland flow basin set in the current unprocessed set list. all , take out the set R1 with the largest area, whose area is S1, calculate the number of sub-basins n that R1 can divide according to the area ratio, and the expected area of ​​the sub-basin divided by R1 is S t . Take the largest internal flow basin from the set R1. If the area of ​​the largest internal flow basin is not less than S t , it is directly used as a new set R2; otherwise, it is used as a seed to loop through other adjacent basins and calculate the total area until the total area is closest to the expected area St, forming a new set R2; set R2 is encoded separately, and the difference set R1-R2 between set R1 and set R2 is analyzed, and the unconnected sets composed of the remaining uncoded inland flow basins are counted, added to the unprocessed set list, and the number of subsets that have not been divided and encoded N=N-1 is updated. If N is greater than 0, repeat this step until N=0. Finally, if the unprocessed list is not empty, those unprocessed inland flow basins are merged into the adjacent coded basins through the lowest point on the basin boundary, and the division is stopped.

[0109] In one embodiment, constructing a sub-basin set based on a key inland flow basin and encoding the sub-basin set separately comprises the following steps:

[0110] S2421. If the area of ​​the key inland flow basin is greater than or equal to the expected area, the key inland flow basin is taken as a new set; otherwise, the adjacent basins are merged based on the adjacent relationship with the key inland flow basin as a seed;

[0111] S2422. Based on the merging result of adjacent watersheds, a sub-watershed set is constructed, and the area of ​​the sub-watershed set is calculated;

[0112] S2423. Repeat steps S2421 and S2422 until the area of ​​the sub-basin set meets the expected area.

[0113] Specifically, Figure 4 As shown in the figure, it shows the specific process of decomposing a set of internal flow basins into four sub-sets of internal flow basins, where the numbers represent the areas of the internal flow basins, such as Figure 4 As shown in (a), initially there is only one inland flow basin set with an area of ​​25, of which the largest inland flow basin has an area of ​​9, which is larger than the expected area of ​​6.25 for the current division. The code steps for calculating the expected area of ​​the current division are as follows:

[0114] N=4; n=4*9 / 25=1; S1=9 / n=9 / 1=9

[0115] N=3; n=3*12 / 16=2; S t =12 / 2=6

[0116] N=2; n=2*5 / 9=1; S t =5 / 1=5

[0117] N=1; n=1*4 / 6=1; S t =4 / 1=4

[0118] N=0;Break;

[0119] Thus, the seed basin with an area of ​​9 in this embodiment is directly encoded, and then Figure 4 As shown in (b), after 9 inland flow basins are encoded, the remaining inland flow basins are divided into two unconnected areas in the upper left and lower right, with areas of 4 and 12 respectively, which need to be divided into 1 and 2 subsets respectively. The uncoded inland flow basin set with a larger area in the lower right is processed first, and the inland flow basin with an area of ​​4 is taken as the seed. After merging the two inland flow basins with an area of ​​1 on the left, the area is equal to the expected value of 6, and the merging encoding is stopped.

[0120] Specifically, Figure 4 As shown in (c) and (d), after processing, the remaining uncoded inland flow basins in the above embodiment are divided into 3 areas, with areas of 5, 4, and 1 from large to small. Then, according to the area ratio, the areas with areas of 5 and 4 are each divided into 1 subset, so they can be directly encoded. The remaining uncoded basins are merged into the adjacent coded basins through the lowest elevation point on their boundaries. The final secondary division result is shown as follows: Figure 4 As shown in (e).

[0121] In one embodiment, dividing the outer flow basin and encoding it, and then merging the uncoded inner flow basin into the adjacent coded basin based on the lowest point of the boundary includes the following steps:

[0122] S31. Use the Pfafstetter watershed coding algorithm to divide and code coastal watersheds;

[0123] Specifically, the Pfafstetter method is used in this embodiment to divide the coastal basins in the external flow basin and encode them. The encoding method of the Pfafstetter method for processing coastal basins is: determine the spatial topological relationship of the internal flow basins in the current level basin, and combine adjacent internal flow basins into an internal flow basin set; if there are coastal basins in the current level basin, Pfafstetter coding is used to process the coastal basins for secondary basin division. First, the four largest external flow basins in the current basin are selected and encoded as "2, 4, 6, 8" respectively. At this time, the original basin is divided into four intermediate basins by the above four external flow basins and one internal flow basin set. These four intermediate basins are merged into a basin set and encoded as "1, 3, 5, 7" respectively.

[0124] S32, divide and code general watersheds;

[0125] S33. Based on the lowest point of the boundary of the uncoded watershed set, merge the uncoded watershed into the adjacent coded watershed.

[0126] In one embodiment, dividing the general flow domain and encoding it includes the following steps:

[0127] S321, based on the general outflow basin, trace back along the main stream from the basin outlet to the river source;

[0128] S322. Compare the size of the upstream drainage area at the confluence of the river during the tracing process to determine the main stream and tributaries;

[0129] S323, based on the determined tributaries, select and encode several tributaries with the largest catchment areas, and divide the general river basin into several intermediate general river basins according to the encoded tributaries, and encode the intermediate general river basins;

[0130] S324. Based on the lowest elevation point on the watershed boundary, merge the uncoded inland flow watershed into the adjacent coded watershed.

[0131] Specifically, the Pfafstetter method is used in this embodiment to divide the general basins in the external flow basin. The coding method of the Pfafstetter method for processing the general basin is: trace back from the estuary to the source of the river. When encountering a river intersection, the one with a larger upstream area is taken as the main stream, and the one with a smaller area is taken as the tributary. The position of the tributary is recorded, and then the trace is continued upstream along the main stream. If the river intersection is encountered again, the previous step is repeated until the source of the river is traced back; among all the recorded tributaries, the four tributaries with the largest catchment areas are selected, and their corresponding basins are coded as 2, 4, 6, and 8 in order from near to far from the estuary. At this time, the original basin is divided into 5 intermediate basins by the above 4 tributary basins, and these 5 intermediate basins are also coded as 1, 3, 5, 7, and 9 in order from near to far from the estuary; the remaining uncoded internal flow basins are merged into adjacent coded basins through the lowest elevation point on the basin boundary.

[0132] In one embodiment, based on the lowest point of the boundary of the uncoded watershed set, merging the uncoded watershed into the adjacent coded watershed comprises the following steps:

[0133] S331, traverse the boundary pixels of the uncoded watershed set;

[0134] S332, based on the traversal result, determining the pixel position where the minimum elevation value is located;

[0135] S333. Based on the pixel position where the minimum elevation value is located, merge the uncoded watershed set into the nearest coded watershed in a clockwise direction.

[0136] Specifically, by nesting the inland watershed, the inland watershed set is decomposed into separate inland watersheds. In the above embodiment, the Pfafstetter coding method is used to divide them. First, the end point of the inland river is taken as the exit point, and the river source is traced back from the exit point. When the river channel is encountered, the upstream with a larger area is taken as the main stream, and the upstream with a smaller area is taken as the tributary. The position of the tributary is recorded, and then the trace is continued upstream along the main stream; if the river channel is encountered again, the previous step is repeated until the river source is traced back; then, among all the recorded tributaries, 4 tributaries with the largest catchment area are selected, and in the order from near to far from the estuary, in this embodiment, their corresponding watersheds are coded as 2, 4, 6, and 8 respectively; finally, the remaining watersheds are also coded as 1, 3, 5, 7, and 9 in order from near to far from the estuary, so that the division of the secondary watershed is completed. If the area of ​​the divided secondary watershed is less than the user-specified threshold, the division is stopped, otherwise, this step is repeated to achieve the nested division of a single sub-basin until it stops.

[0137] In one embodiment, for a single inland flow basin whose area is greater than a threshold, the Pfafstetter method is used to process the inland flow basin to divide the secondary watershed until the area of ​​the secondary inland flow basin is less than or equal to the threshold, which includes the following steps:

[0138] S41. Trace back from the end of the river to the source of the river. When you encounter a river intersection, take the one with a larger upstream area as the main stream and the one with a smaller upstream area as the tributary. Record the location of the tributary and continue tracing upstream along the main stream until you reach the source of the river.

[0139] S42. Among all the recorded tributaries, select the four tributaries with the largest catchment areas as tributary basins, and code the tributary basins as 2, 4, 6, and 8 in order from near to far from the river terminal;

[0140] S43, based on the tributary basins, the original basin is divided into five intermediate basins, and the intermediate basins are coded as 1, 3, 5, 7, and 9 in order from near to far from the river terminal;

[0141] S44. Compare the secondary internal flow basin area with the threshold. If the secondary internal flow basin area is larger than the threshold, repeat steps S41 to S43 until the secondary internal flow basin area is smaller than or equal to the threshold.

[0142] Specifically, the effect of nested division of internal flow basins is as follows: Figure 5 As shown, it can be seen that: compared with the existing methods, the nested division method of inland flow basins based on set thinking proposed in the present invention can be applied to areas with a large number of inland flow basins, and can automatically perform nested division of inland flow basins to obtain inland flow basin boundaries of multiple levels, which has broad application prospects in terrain analysis, watershed simulation, etc.

[0143] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A nested division method of inland flow basin based on set concept, characterized in that: The nested division method of the internal flow basin based on the set concept includes the following steps: S1. Extract the internal flow basin range based on the digital elevation model; S2. Merge adjacent internal flow basins to construct an internal flow basin set, encode the internal flow basin set with the largest area, and nest and divide it until the number of internal flow basins at each level is less than or equal to 10; S3, divide the outflow basin and encode it, and then merge the uncoded inflow basin into the adjacent coded basin based on the lowest point of the boundary; S4. For a single internal flow basin whose area is larger than the threshold, the secondary watershed is divided by using the Pfafstetter method to process the internal flow basin until the area of ​​the secondary internal flow basin is less than or equal to the threshold; The method of merging adjacent inland flow basins, constructing an inland flow basin set, encoding and nesting the inland flow basin set with the largest area until the number of inland flow basins at each level is less than or equal to 10 includes the following steps: S21, extracting the scope and boundary of each inland flow basin, and traversing the adjacent basins of each inland flow basin; S22, merging adjacent inland flow basins according to the traversal results to obtain an inland flow basin set, and establishing an unprocessed basin set list, and adding the inland flow basin set with the largest area to the unprocessed basin set list; S23, calculating the area of ​​the inland flow basin set in the unprocessed basin set list, determining the expected number and expected area of ​​the secondary basin divisions, and constructing the key inland flow basin set; S24, according to the nested division rule, based on the calculation results, the key internal flow basin set is divided into secondary basins and coded; The calculation of the area of ​​the inland flow basin set in the unprocessed basin set list, the determination of the expected number and area of ​​the secondary basin divisions, and the construction of the key inland flow basin set include the following steps: S231, calculating the total area of ​​the inland flow basin sets and the area of ​​each inland flow basin set in the unprocessed basin set list; S232. Calculate the expected number of sub-basins and their expected areas according to the area ratio; S233, select the largest inland watershed set and construct the key inland watershed set; The method of performing secondary watershed division coding on the key inland watershed set based on the calculation results according to the nested division rule comprises the following steps: S241. Based on the set of key inland flow basins, select the inland flow basin with the largest area to construct the key inland flow basins; S242. Based on the key inland flow basins, construct a sub-basin set and encode the sub-basin set separately; S243, according to the neighboring relationship, merge the uncoded inland flow basins into a new basin set, add it to the unprocessed basin set list, and update the expected number of sub-basin divisions; S244, repeating steps S241 to S243 until the expected number of sub-basins to be divided is 0; S245. If the unprocessed watershed set list is not empty, the unprocessed inland watersheds in the unprocessed watershed set list are merged into adjacent coded watersheds through the lowest point on the watershed boundary, and the division is stopped.

2. The method for nested division of inland flow basins based on set concept according to claim 1 is characterized in that: The extraction of the internal flow basin range based on the digital elevation model includes the following steps: S11. Based on the digital elevation model, the single flow direction algorithm is used to calculate the flow direction and the cumulative amount of confluence, and the river network is extracted according to the preset threshold; S12. Based on the extracted river network, mark the rivers whose end points are located on land and have no downstream as inland rivers, and mark the upstream catchment areas of inland rivers as endorheic basins, and mark the upstream catchment areas of non-inland rivers as endorheic basins.

3. The method for nested division of inland flow basins based on set concept according to claim 1 is characterized in that: The method of constructing a sub-basin set based on the key inland flow basin and encoding the sub-basin set separately includes the following steps: S2421. If the area of ​​the key inland flow basin is greater than or equal to the expected area, the key inland flow basin is taken as a new set; otherwise, the adjacent basins are merged based on the adjacent relationship with the key inland flow basin as a seed; S2422. Based on the merging result of adjacent watersheds, a sub-watershed set is constructed, and the area of ​​the sub-watershed set is calculated; S2423. Repeat steps S2421 and S2422 until the area of ​​the sub-basin set meets the expected area.

4. The method for nested division of inland flow basins based on set concept according to claim 1 is characterized in that: The method of dividing the external flow basin and encoding it, and then merging the uncoded internal flow basin into the adjacent coded basin based on the lowest point of the boundary comprises the following steps: S31. Use the Pfafstetter watershed coding algorithm to divide and code coastal watersheds; S32, divide and code general watersheds; S33. Based on the lowest point of the boundary of the uncoded watershed set, merge the uncoded watershed into the adjacent coded watershed.

5. The method for nested division of inland flow basins based on set concept according to claim 4 is characterized in that: The general watershed division and coding comprises the following steps: S321, based on the general outflow basin, trace back along the main stream from the basin outlet to the river source; S322. Compare the size of the upstream drainage area at the confluence of the river during the tracing process to determine the main stream and tributaries; S323, based on the determined tributaries, select and encode several tributaries with the largest catchment areas, and divide the general river basin into several intermediate general river basins according to the encoded tributaries, and encode the intermediate general river basins; S324. Based on the lowest elevation point on the watershed boundary, merge the uncoded inland flow watershed into the adjacent coded watershed.

6. The method for nested division of inland flow basins based on set concept according to claim 5 is characterized in that: The step of merging the uncoded watershed into the adjacent coded watershed based on the lowest boundary point of the uncoded watershed set comprises the following steps: S331, traverse the boundary pixels of the uncoded watershed set; S332, based on the traversal result, determining the pixel position where the minimum elevation value is located; S333. Based on the pixel position where the minimum elevation value is located, merge the uncoded watershed set into the nearest coded watershed in a clockwise direction.

7. The method for nested division of inland flow basins based on set concept according to claim 1 is characterized in that: The method of dividing a single internal flow basin whose area is larger than the threshold value into secondary watersheds by using the Pfafstetter method to process the internal flow basin until the area of ​​the secondary internal flow basin is less than or equal to the threshold value comprises the following steps: S41. Trace back from the end of the river to the source of the river. When you encounter a river intersection, determine the main stream and tributaries based on the size of the upstream area, record the location of the tributaries, and continue tracing upstream along the main stream until you reach the source of the river; S42. Among all the recorded tributaries, select the four tributaries with the largest catchment areas as tributary basins, and code the tributary basins as 2, 4, 6, and 8 in order from near to far from the river terminal; S43, based on the tributary basins, the original basin is divided into five intermediate basins, and the intermediate basins are coded as 1, 3, 5, 7, and 9 in order from near to far from the river terminal; S44. Compare the secondary internal flow basin area with the threshold. If the secondary internal flow basin area is larger than the threshold, repeat steps S41 to S43 until the secondary internal flow basin area is smaller than or equal to the threshold.

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