DEM (Digital Elevation Model) synthesis method and device based on terrain internal structure, equipment and medium

Abstract

The embodiment of the invention provides a digital elevation model (DEM) synthesis method and device based on a terrain internal structure, equipment and a medium, and belongs to the technical field of hydrology and geography. The method comprises the following steps: iteratively performing mainstream identification by taking a hydrological network in original terrain elevation data as an identification object to obtain a river set, wherein the river set comprises a plurality of rivers and a topological relation of the rivers; setting river grades according to the topological relation; constructing a multi-stage drainage basin set based on river grades; selecting a target drainage basin set according to the number of ideal drainage basins for topographic feature point extraction; and establishing a digital elevation model by using an extraction result. The river set obtained by the embodiment of the invention comprises mainstreams of different scale regions in the hydrological network, the vigor structure of the hydrological network can be effectively extracted, the surface form characteristics are accurately extracted on the basis of the vigor structure of the hydrological network, and original data characteristics can be reserved as far as possible while the DEM terrain is simplified.

Description

Technical Field

[0001] The present application relates to the field of hydrogeographic technology, and in particular to a DEM integration method and device, equipment and medium based on the intrinsic structure of terrain. Background Art

[0002] Digital Elevation Model (DEM), as a digital expression of the earth's surface terrain elevation, is widely used in scientific research and production fields such as surveying and mapping, hydrology, meteorology, and engineering construction. In order to meet the diverse needs for terrain accuracy and data size in different usage scenarios, countries generally adopt a multi-scale coexistence method to establish a multi-scale DEM database.

[0003] The traditional multi-scale DEM database is constructed in a multi-database multi-version manner, that is, DEM data of each scale is collected independently to establish a DEM database. With the update and improvement of spatial data acquisition methods such as lidar, terrain data has increased significantly in terms of data volume, acquisition frequency, complexity, etc. The traditional multi-database multi-version database construction method gradually presents drawbacks such as data redundancy, poor consistency, difficulty in updating, and waste of manpower, financial resources, etc. To solve these drawbacks, a more ideal way is to only establish a high-precision large-scale database, and use DEM terrain automatic synthesis technology to extract and export other small-scale data from the large-scale data. This method requires simplifying large-scale data into different small-scale data while retaining the original data characteristics. Therefore, how to retain the original data characteristics as much as possible while simplifying the DEM terrain has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The main purpose of the embodiments of the present application is to propose a DEM synthesis method and device, equipment and medium based on the intrinsic structure of the terrain, aiming to simplify the DEM terrain while retaining the original data characteristics as much as possible.

[0005] To achieve the above purpose, a first aspect of an embodiment of the present application proposes a DEM integration method based on the intrinsic structure of the terrain, the method comprising:

[0006] Get the original terrain elevation data;

[0007] identifying a hydrological network in the original terrain elevation data, the hydrological network comprising a plurality of river segments;

[0008] Iteratively perform mainstream identification on the hydrological network as the identification object, and obtain at least one identification result in each round of mainstream identification, wherein the identification result includes a river and a plurality of sub-hydrological networks; each of the sub-hydrological networks is used as the identification object of the next round of mainstream identification until an iteration stop condition is reached; after the iteration is completed, a river set is obtained, wherein the river set includes a plurality of the rivers and the topological relationship between the rivers;

[0009] According to the topological relationship, setting a river level for each river;

[0010] For rivers with a river grade not less than i (i = 1, 2, ...), the catchment area of ​​each river is extracted as the i-level basin, and the i-level basin set is obtained;

[0011] Get the ideal number of watersheds;

[0012] Selecting an n-level watershed set whose watershed number is closest to the ideal watershed number as the target watershed set;

[0013] Extract terrain feature points from the target watershed set;

[0014] The digital elevation model is established using the extracted terrain feature points.

[0015] In some embodiments, the method further includes: performing data preprocessing on the original terrain elevation data; the data preprocessing on the original terrain elevation data includes:

[0016] Extract depressions from the original terrain elevation data; calculate the depression depth of each depression to obtain a depression depth set; use the head-tail segmentation method to segment the depression depth set into a head set and a tail set; select the depression corresponding to the tail set as an unnaturally formed depression and fill the unnaturally formed depression.

[0017] In some embodiments, identifying a hydrological network in the raw terrain elevation data includes:

[0018] Calculate the water flow direction of each grid in the original terrain elevation data; traverse each grid according to the water flow direction, calculate the cumulative flow of each grid, and obtain a cumulative flow set; use the head-tail segmentation method to iteratively segment the cumulative flow set into a head set and a tail set until the iteration stop condition is met; determine the river section threshold according to the average value of the tail set; perform vectorization operation on the grid whose cumulative flow value is greater than the river section threshold, and obtain a directed polyline set, each directed polyline is a river section.

[0019] In some embodiments, the mainstream identification includes:

[0020] The longest river path in the identified object is extracted as the initial mainstream; the initial mainstream is removed from the identified object, and the remaining river sections are divided into multiple sub-hydrological networks according to the connection relationship; the longest river path in each sub-hydrological network is extracted as the alternative mainstream; the importance of each alternative mainstream relative to the initial mainstream is calculated based on the path length and path angle; if the maximum importance is a positive value, the alternative mainstream corresponding to the maximum importance is output as the river; otherwise, the initial mainstream is output as the river.

[0021] In some embodiments, setting a river level for each river according to the topological relationship includes:

[0022] Set the river that is connected to other rivers only at the terminal outlet as a level 1 river;

[0023] Remove j (j=1, 2, ...) level rivers, and set the remaining rivers that are connected to other rivers only at their terminal outlets as j+1 level rivers, with j increasing by 1. Repeat this step until all rivers are assigned levels.

[0024] In some embodiments, the method further includes: in the i-level watershed set, if the watershed area of ​​a low-level river overlaps with the watershed area of ​​a high-level river, the watershed area of ​​the high-level river is changed to a non-overlapping area.

[0025] In some embodiments, obtaining the ideal number of watersheds includes: obtaining a ratio of a target scale to an original scale; and determining the ideal number of watersheds based on the ratio and the number of first-level watersheds.

[0026] In some embodiments, it also includes: calculating the river quantity adjustment amount based on the difference between the ideal river basin quantity and the river basin quantity of the target river basin set; obtaining a number of target rivers whose quantity is the river adjustment quantity; and increasing or decreasing the catchment area of ​​the target river in the target river basin set.

[0027] In some embodiments, the terrain feature points include: mountain top points, depression points, ridge lines, valley bottom lines, saddle points, ridge line nodes and valley bottom line nodes; the ridge line nodes are grid points in the ridge line of the watershed that are adjacent to at least two adjacent watersheds; the valley bottom line nodes are grid points at the intersection of two valley bottom lines in the watershed.

[0028] In some embodiments, the method further includes: setting the level of each terrain feature point, and filtering out terrain feature points whose level is lower than a preset level threshold; the method of setting the level of each terrain feature point includes:

[0029] Set the levels of the mountain top, depression, saddle, valley bottom, and ridgeline nodes;

[0030] Obtain a feature point set including all terrain feature points; calculate the convex hull of the feature point set, and set the levels of the terrain feature points corresponding to the convex hull vertices;

[0031] Constructing a triangular mesh using the terrain feature points of the set level, wherein the triangular mesh includes a plurality of triangles;

[0032] Calculate the two-dimensional plane projection of each ungraded terrain feature point; calculate the two-dimensional plane projection of each triangle; determine in turn whether the two-dimensional plane projection of each ungraded terrain feature point is within the two-dimensional plane projection of the triangle, and if so, construct a corresponding relationship between the ungraded terrain feature point and the triangle;

[0033] Traverse all triangles, calculate the distance from the current triangle to the corresponding ungraded terrain feature point, take the point with the largest distance as the candidate point, and obtain a candidate point set; filter the candidate point set according to a preset distance threshold to obtain a salient point set; set the level of each salient point; use the salient points to update the triangular mesh to obtain the levels of the remaining ungraded terrain feature points.

[0034] To achieve the above purpose, the second aspect of the embodiment of the present application proposes a DEM synthesis device based on the intrinsic structure of the terrain, the device comprising:

[0035] A data acquisition module is used to obtain original terrain elevation data;

[0036] A hydrological network identification module, used for identifying a hydrological network in the original terrain elevation data, wherein the hydrological network includes a plurality of river sections;

[0037] The river extraction module is used to iteratively identify the mainstream by taking the hydrological network as the identification object, and obtain at least one identification result in each round of mainstream identification, and the identification result includes a river and a plurality of sub-hydrological networks; each of the sub-hydrological networks is used as the identification object of the next round of mainstream identification until the iteration stop condition is reached; after the iteration is completed, a river set is obtained, and the river set includes a plurality of the rivers and the topological relationship between the rivers;

[0038] The watershed construction module is used to extract the catchment area of ​​each river as the i-level watershed for rivers with a river level not less than i (i = 1, 2...), and obtain the i-level watershed set;

[0039] The model reconstruction module is used to obtain the ideal number of watersheds; select the n-level watershed set whose watershed number is closest to the ideal number of watersheds as the target watershed set; extract terrain feature points from the target watershed set; and establish a digital elevation model using the extracted terrain feature points.

[0040] To achieve the above objectives, a third aspect of an embodiment of the present application proposes an electronic device, which includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the method described in the first aspect is implemented.

[0041] To achieve the above-mentioned purpose, the fourth aspect of an embodiment of the present application proposes a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method described in the first aspect is implemented.

[0042] The DEM integration method, device, equipment and medium based on the intrinsic structure of terrain proposed in the present application iteratively divides the hydrological network into sub-hydrological networks for mainstream identification, extracts the mainstreams of different scale areas in the hydrological network as rivers, and the obtained river set reflects the vitality structure of the hydrological network; then the rivers are classified according to the topological relationship of the rivers, and a multi-level basin set is constructed based on the multi-level rivers, and the high-level basin set is nested in the low-level basin set, which fully considers the interaction between the river and the surface morphology, and extracts the nested substructure of the basin based on the vitality structure of the hydrological network, and clarifies the inherent hierarchical relationship between the basins; then the corresponding level target basin set is selected according to the ideal number of basins to extract terrain feature points to reconstruct the digital elevation model, and the surface morphological characteristics are accurately extracted on the basis of the vitality structure of the hydrological network, which can simplify the DEM terrain while retaining the original data characteristics as much as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a flow chart of a DEM synthesis method based on the intrinsic structure of terrain provided in an embodiment of the present application;

[0044] Figure 2 is a schematic diagram showing original terrain elevation data in an embodiment of the present disclosure;

[0045] Figure 3 This is a diagram showing an embodiment of the present disclosure. Figure 2 Schematic diagram of the original terrain elevation data after the depression is filled;

[0046] Figure 4 This is a diagram showing an embodiment of the present disclosure according to Figure 3 Schematic diagram of water flow direction obtained from terrain elevation data;

[0047] Figure 5 This is a diagram showing an embodiment of the present disclosure according to Figure 4 Schematic diagram of the accumulated flow obtained by the water flow direction;

[0048] Figure 6 This is a diagram showing an embodiment of the present disclosure according to Figure 5Schematic diagram of the hydrological network obtained from the cumulative flow;

[0049] Figure 7 This is a diagram showing an embodiment of the present disclosure according to Figure 6 Schematic diagram of the initial mainstream obtained from the hydrological network;

[0050] Figure 8 This is a diagram showing an embodiment of the present disclosure according to Figure 7 Schematic diagram of alternative mainstreams obtained from the initial mainstream;

[0051] Fig. 9 This is an example of the present disclosure. Figure 7 Initial mainstream and Figure 8 Schematic diagram of the angle between the alternative mainstreams;

[0052] Fig.10 This is a diagram showing an embodiment of the present disclosure according to Figure 6 Schematic diagram of the river obtained from the hydrological network;

[0053] Fig.11 This is a diagram showing an embodiment of the present disclosure according to Figure 6 Schematic diagram of the river set obtained from the hydrological network;

[0054] Fig.12 This is a diagram showing an embodiment of the present disclosure according to Fig.11 Schematic diagram of the first-level rivers obtained from the river set;

[0055] Fig.13 This is a diagram showing an embodiment of the present disclosure according to Fig.12 Schematic diagram of the second-level river obtained from the first-level river;

[0056] Fig.14 This is a diagram showing an embodiment of the present disclosure according to Fig.13 Schematic diagram of the third-level river obtained from the second-level river;

[0057] Fig.15 This is a diagram showing an embodiment of the present disclosure according to Fig.14 Schematic diagram of the 4th level river obtained from the 3rd level river;

[0058] Fig.16 This is a diagram showing an embodiment of the present disclosure according to Fig.15 Schematic diagram of the first-level basin obtained from the river hierarchy in;

[0059] Fig.17 This is a diagram showing an embodiment of the present disclosure according to Fig.15 Schematic diagram of the second-level basin obtained from the river hierarchy in;

[0060] Fig.18 This is a diagram showing an embodiment of the present disclosure according to Fig.15Schematic diagram of the 3rd level watershed obtained from the river hierarchy in;

[0061] Fig.19 This is a diagram showing an embodiment of the present disclosure according to Fig.15 Schematic diagram of the 4-level watershed obtained from the river hierarchy in;

[0062] Fig. 20 is a schematic diagram showing a mountain top point in an embodiment of the present disclosure;

[0063] Fig.21 is a schematic diagram showing a depression point in an embodiment of the present disclosure;

[0064] Fig. 22 is a schematic diagram showing a ridgeline in an embodiment of the present disclosure;

[0065] Fig.23 is a schematic diagram showing a valley bottom line in an embodiment of the present disclosure;

[0066] Fig.24 is a schematic diagram showing a saddle point in an embodiment of the present disclosure;

[0067] Fig.25 is a schematic diagram showing a ridgeline node in an embodiment of the present disclosure;

[0068] Fig.26 is a schematic diagram showing a valley bottom line node in an embodiment of the present disclosure;

[0069] Fig. 27 is a schematic diagram showing the topographic features of a 4-level watershed in an embodiment of the present disclosure;

[0070] Fig.28 is a schematic diagram showing the topographic features of three level 3 watersheds in an embodiment of the present disclosure;

[0071] Fig.29 is a schematic diagram showing a Delaunay triangulated mesh in an embodiment of the present disclosure;

[0072] Fig.30 This is a diagram showing an embodiment of the present disclosure according to Fig.29 Schematic diagram of the salient points obtained by Delaunay triangular mesh screening;

[0073] Fig.31 Schematic diagram showing the DEM synthesis result in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0074] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0075] It should be noted that, although the functional modules are divided in the device schematic diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flowchart. The terms "first", "second", etc. in the specification, claims and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0076] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0077] First, some nouns involved in this application are analyzed:

[0078] Watershed: An area surrounded by a watershed as its boundary. The runoff in the area is concentrated at the lowest point in the area. Each watershed is an independent hydrological unit.

[0079] Hydrologic Network: refers to the interconnected network system composed of rivers, streams, lakes, reservoirs and other water bodies in the surface hydrological cycle, which are interconnected through the natural movement of water.

[0080] Mainstream Identification: refers to identifying the main flow path in a river system, that is, identifying the main rivers in the basin.

[0081] Stream Order: refers to the numerical ranking assigned to a river based on factors such as the number of tributaries, confluence patterns, etc. Stream Order can characterize certain characteristics of a river; for example, a Class 1 river is primarily an overland flow with no concentrated upstream flow.

[0082] Dynamic Structure: refers to a multi-level, closely connected structural system formed by various elements contained within an object. Dynamic structure reflects the internal organization of an object. A dynamic structure contains substructures of different levels, and each substructure also contains substructures of smaller levels. The number of substructures and the level of substructures jointly determine the vitality of the dynamic structure.

[0083] The existing DEM terrain synthesis methods can be divided into two types according to the size of the terrain range considered when simplifying elements: terrain simplification methods based on local neighborhoods and terrain simplification methods based on global structures.

[0084] There are two main types of terrain simplification methods based on local neighborhoods: global filtering methods based on smooth filters and feature selection methods based on local areas. The former includes downsampling methods, low-channel filtering methods, wavelet analysis methods, etc. This method performs the same smoothing operation on all elements, resulting in distortion of the terrain skeleton and failing to achieve the effect of extracting the main form and discarding the secondary form. The latter includes hierarchical methods, important point methods, selective filtering methods, etc. These methods mainly determine whether terrain elements are retained based on the degree of morphological changes between local terrains, but cannot identify global features that do not change much in local terrain.

[0085] The DEM terrain simplification method based on global structure considers the relationship between terrain elements from the perspective of the entire terrain, including methods that consider geometric features and methods that consider terrain structure. Among them, the method that considers geometric features includes the three-dimensional Douglas-Peucher algorithm. This method determines the selection of terrain points by iteratively judging the distance between three-dimensional terrain points and a specific base surface, thereby extracting important terrain feature points that meet the conditions and can better maintain the overall contour of the terrain. However, the selection of terrain feature points does not consider the semantic characteristics of the terrain, and cannot guarantee the extraction of geographical elements such as peak points, depression points, ridge lines, and river valley lines. In addition, the terrain threshold of this algorithm is affected by many aspects such as terrain range, terrain undulation, and screening ratio. It needs to be manually set by the cartographer, and the degree of automation is low. The method that considers terrain structure first identifies and extracts the implicit terrain features in the DEM data, then evaluates their importance, determines the terrain features that need to be retained, and reconstructs the simplified DEM on this basis. For example, the valley filling algorithm proposed by Ai Tinghua and the DEM comprehensive method based on watershed merging proposed by Li Jingzhong. However, current research rarely considers the multi-level structural characteristics of terrain structure, lacks systematic consideration and quantitative distinction of the importance of terrain structure in the process of terrain simplification, and lacks comprehensive research on terrain characteristics and their transformation in corresponding DEM models. Based on this, the present application embodiment provides a DEM synthesis method and device, equipment and medium based on the intrinsic structure of terrain, aiming to simplify the DEM terrain while retaining the original data characteristics as much as possible.

[0086] The DEM integration method, device, equipment and medium based on the intrinsic structure of terrain provided in the embodiments of the present application are specifically illustrated through the following embodiments. First, the DEM integration method based on the intrinsic structure of terrain in the embodiments of the present application is described.

[0087] The DEM synthesis method based on the intrinsic structure of the terrain provided in the embodiment of the present application relates to the field of hydrological geography technology. The DEM synthesis method based on the intrinsic structure of the terrain provided in the embodiment of the present application can be applied to a terminal, can also be applied to a server side, and can also be software running in a terminal or a server side. In some embodiments, the terminal can be a smart phone, a tablet computer, a laptop computer, a desktop computer, etc.; the server side can be configured as an independent physical server, or can be configured as a server cluster or a distributed system composed of multiple physical servers, and can also be configured as a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, CDN, and big data and artificial intelligence platforms; the software can be an application that implements the DEM synthesis method based on the intrinsic structure of the terrain, etc., but is not limited to the above forms.

[0088] The present application can be used in many general or special computer system environments or configurations. For example: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments including any of the above systems or devices, etc. The present application can be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. The present application can also be practiced in distributed computing environments, in which tasks are performed by remote processing devices connected through a communication network. In a distributed computing environment, program modules can be located in local and remote computer storage media including storage devices.

[0089] Figure 1 is an optional flow chart of a DEM synthesis method based on the intrinsic structure of terrain provided in an embodiment of the present application. Figure 1 The method may include but is not limited to steps S101 to S109.

[0090] Step S101, obtaining original terrain elevation data;

[0091] Step S102, identifying a hydrological network in the original terrain elevation data, wherein the hydrological network includes a plurality of river sections;

[0092] Step S103, iteratively performing mainstream identification on the hydrological network as an identification object, obtaining at least one identification result in each round of mainstream identification, wherein the identification result includes a river and a plurality of sub-hydrological networks; each of the sub-hydrological networks is used as an identification object for the next round of mainstream identification until an iteration stop condition is reached; after the iteration is completed, a river set is obtained, wherein the river set includes a plurality of the rivers and the topological relationships between the rivers;

[0093] Step S104, setting a river level for each river according to the topological relationship;

[0094] Step S105, for rivers with a river grade not less than i (i=1, 2, ...), extract the catchment area of ​​each river as an i-level basin, and obtain an i-level basin set;

[0095] Step S106, obtaining the ideal watershed quantity;

[0096] Step S107, selecting an n-level watershed set whose watershed number is closest to the ideal watershed number as a target watershed set;

[0097] Step S108, extracting terrain feature points from the target watershed set;

[0098] Step S109: establishing a digital elevation model using the extracted terrain feature points.

[0099] Steps S101 to S109 shown in the embodiment of the present application iteratively divide the hydrological network into sub-hydrological networks for mainstream identification, extract the mainstreams of different scale areas in the hydrological network as rivers, and the obtained river set reflects the vitality structure of the hydrological network; then the rivers are classified according to the topological relationship of the rivers, and a multi-level basin set is constructed based on the multi-level rivers, and the high-level basin set is nested in the low-level basin set, which fully considers the interaction between the river and the surface morphology, and extracts the nested substructure within the basin based on the vitality structure of the hydrological network, and clarifies the inherent hierarchical relationship between the basins; then, according to the ideal number of basins, the corresponding level target basin set is selected to extract terrain feature points to reconstruct the digital elevation model, and the surface morphological characteristics are accurately extracted based on the vitality structure of the hydrological network, which can simplify the DEM terrain while retaining the original data characteristics as much as possible.

[0100] After step S101 in some embodiments, the DEM synthesis method based on the intrinsic structure of the terrain further includes: performing data preprocessing on the original terrain elevation data. The data preprocessing may be data clipping or depression filling, but is not limited thereto.

[0101] In some embodiments, the data preprocessing is depression filling, and the data preprocessing of the original terrain elevation data may include but is not limited to steps S201 to S204:

[0102] Step S201, extracting depressions from original terrain elevation data;

[0103] Step S202, calculating the depression depth of each depression to obtain a depression depth set;

[0104] Step S203, using the head-tail segmentation method to segment the depression depth set into a head set and a tail set;

[0105] Step S204, selecting the depression corresponding to the tail set as an unnaturally formed depression, and filling the unnaturally formed depression.

[0106] In a large area of ​​terrain, due to the errors caused by data accuracy and collection, there may be a large number of depressions with very small depths, i.e., unnatural depressions. Steps S201 to S204 shown in the embodiment of the present application identify unnatural depressions through the head-to-tail segmentation method, which does not rely on the manually set depression depth threshold but automatically identifies unnatural depressions based on the inherent structural characteristics of the data, avoiding subjective human decision-making and threshold setting, improving the automation level of the DEM synthesis method, and meeting the needs of high-frequency map updates.

[0107] In some embodiments, step S201 may include but is not limited to: calculating the water flow direction of each grid in the DEM through the D8 algorithm; determining the confluence point according to the water flow direction, the confluence point is the grid point where the water flow direction cannot point to other grids; taking the confluence point as the outlet, tracing back according to the water flow direction, and obtaining the set of all grid points flowing to the confluence point, which is the depression corresponding to the confluence point. Among them, the principle of the D8 algorithm to calculate the flow direction is: the water flow in a grid will flow to the grid that is not higher than the current grid and has the largest slope among the eight adjacent grids. The slope is determined by the ratio of the height difference and the distance between the grids. In this example, the distance of the four grids in the horizontal and vertical directions is set to 1, and the distance in the diagonal direction is set to 2.

[0108] In step S202 of some embodiments, for each depression, the difference between the lowest elevation value of the grids adjacent to the depression and the lowest elevation value of the grid within the depression is calculated as the depth of the current depression.

[0109] by Figure 2 Taking the original terrain elevation data shown in FIG. 1 as an example, the original terrain elevation data is used to fill the depression: the sink point is extracted, such as Figure 2The elevations of the two grid points in row 5, column 9 and row 11, column 5 are lower than those of the grid points in the eight directions around them. These two grid points are recorded as sinks. The depressions corresponding to these two sinks are obtained. The minimum elevations in the two depressions are 18 and 11 respectively, and the minimum elevations in the adjacent grids are 19 and 12 respectively. Therefore, the depths of the two depressions are both 1. These two depressions are not naturally formed. They are filled and the minimum values ​​in the depression grids are replaced with 19 and 12 respectively. Figure 3 After the depressions are filled, water can continue to flow to the adjacent minimum elevation grid when flowing through these depressions, without causing unnatural disconnection of the river network.

[0110] In some embodiments, step S102 may include but is not limited to steps S301 to S305:

[0111] Step S301, calculating the water flow direction of each grid in the original terrain elevation data;

[0112] Step S302, traversing each grid according to the flow direction, calculating the cumulative flow of each grid, and obtaining a cumulative flow set;

[0113] Step S303, using the head-tail segmentation method to iteratively segment the accumulated traffic set into a head set and a tail set until an iteration stop condition is met;

[0114] Step S304, determining the river section threshold according to the average value of the tail set;

[0115] Step S305, performing a vectorization operation on the grids whose cumulative flow value is greater than the river section threshold, to obtain a set of directed polyline segments, each of which is a river section.

[0116] Steps S301 to S305 shown in the embodiment of the present application determine the river section threshold through the head-to-tail segmentation method. It does not rely on the manually set depression depth threshold but automatically identifies the river section based on the intrinsic structural characteristics of the data, avoids human subjective decision-making and threshold setting, improves the automation level of the DEM synthesis method, and can meet the needs of high-frequency map updates.

[0117] In some embodiments, step S302 may include but is not limited to: traversing all grids, finding a grid with no water flowing into it as the source point of the river, and recording the cumulative flow as 0; then tracking the next grid according to the flow direction, and calculating the total number of grids into which water flows into the grid as n (n>0), then the cumulative flow of the grid is calculated as the sum of the cumulative flows in each inflow direction plus n; traversing all grids according to the flow direction until the cumulative flows of all grids are calculated.

[0118] To Figure 3Taking the terrain elevation data of the completed depression filling as an example, the hydrological network in the original terrain elevation data is identified: the water flow direction of each grid is calculated by the D8 algorithm, such as Figure 4 Calculate the cumulative flow of each grid, as shown in Figure 5 As shown in Figure 2. According to the average value of the cumulative flow of 5.55, the cumulative flow set is divided into a head set and a tail set, and the average value of the tail set of 0.42 is taken as the river section threshold. The raster with a cumulative flow value greater than the river section threshold is vectorized to obtain a hydrological network, as shown in Figure 2. Figure 6 shown.

[0119] In some embodiments, mainstream identification in step S103 may include but is not limited to steps S401 to S405:

[0120] Step S401, extracting the longest river path in the identified object as the initial mainstream;

[0121] Step S402, removing the initial mainstream from the identified objects, and dividing the remaining river sections into a plurality of sub-hydrological networks according to the connection relationship;

[0122] Step S403, extracting the longest river path in each sub-hydrological network as a candidate mainstream;

[0123] Step S404, calculating the importance of each candidate mainstream relative to the initial mainstream according to the path length and the path angle;

[0124] Step S405: if the maximum importance value is a positive value, the candidate mainstream corresponding to the maximum importance value is output as a river; otherwise, the initial mainstream is output as a river.

[0125] Steps S401 to S405 shown in the embodiment of the present application select an initial mainstream in the identified object, select alternative paths in the sub-hydrological network of the identified object, and select the best one between the initial mainstream and the alternative mainstream according to the path length and the path angle to output as the mainstream. The influence of both river length and river path morphology is taken into consideration. The obtained mainstream runs through the identified object, reflects the relative low point of the surface morphology of the area where it is located, and is conducive to revealing the surface morphological structure characteristics of the area.

[0126] by Figure 6 Taking the hydrological network shown in FIG. 1 as an example, step S103 may include, but is not limited to, steps S501 to S505:

[0127] Step S501, find all river sections without other water flowing into them, and add the starting points of these river sections into the set S0, such as Figure 7 The blue dot in the figure is the starting point; find a river section that does not flow into other rivers and use its end point as the outlet E, such as Figure 7The red point in is the outlet; calculate the distance from all points in S0 to the outlet E along the river path, and take the longest river path as the initial mainstream p0, as shown in Figure 7 The red polyline in the figure is the initial mainstream.

[0128] Step S502: construct a copy H0 of the hydrological network H, remove the initial mainstream p0 from H0, and divide the remaining river sections in the copy H0 into multiple independent sub-hydrological networks according to whether they are connected or not, such as Figure 8 The red points in the figure are the outlets of each sub-hydrological network, and the blue points are the starting points of each sub-hydrological network. According to step S501, the longest river path in each sub-hydrological network is solved as the candidate mainstream p, such as Figure 8 As shown by the orange polyline in . Add the alternative mainstream p to the set P1.

[0129] Step S503: for each candidate mainstream p in P1, the river length and the river angle are comprehensively considered, and the stream significance index (Stream Significance Index) is calculated according to the following formula:

[0130]

[0131] Where d is the total length of the path of the candidate mainstream p from the starting point to the outlet; d0 is the total length of the path of the initial mainstream p0 from the starting point to the outlet; θ is the angle formed by the candidate mainstream p and the initial mainstream p0 at the intersection, as shown in Fig. 9 In this example, the SSI value of the mainstream path p0 is considered to be 0.

[0132] Step S504, obtaining the maximum SSI value SSI max If SSI max >0, then SSI max The starting point of the alternative mainstream p is taken as the starting point of the river, and the river from the starting point of the river to the outlet E is output; if SSI max ≤0, output the initial mainstream p0 as a river. In this example, SSI max >0, output Fig.10 The red polylines shown are rivers.

[0133] Step S505: remove the rivers from the hydrological network H, and divide the remaining rivers into multiple sub-hydrological networks according to whether they are connected. Take each sub-hydrological network as an identification object, iteratively execute steps S501 to S505 until all river sections are included in different rivers, and obtain a river set such as Fig.11 shown.

[0134] In some embodiments, step S104 may include but is not limited to steps S601 to S602:

[0135] Step S601, setting a river that is connected to other rivers only at its terminal outlet as a level 1 river;

[0136] Step S602, remove the j-level river, set the remaining rivers that are only connected to other rivers at the terminal outlet as j+1-level rivers (j=1, 2...), j increases by 1, and repeat this step until all rivers are assigned levels.

[0137] Steps S601 to S602 shown in the embodiment of the present application divide the watershed based on the catchment area corresponding to the river outlet, and extract the vitality structure of the watershed; the division of the watershed is determined by extracting the inherent hierarchical structure, avoiding human subjective decision-making and threshold setting, improving the level of automation, and meeting the needs of high-frequency map updates.

[0138] by Fig.11 Taking the river set shown in FIG. 1 as an example, step S104 may include, but is not limited to, steps S701 to S704:

[0139] Step S701: for the set R0 consisting of all rivers, find all rivers that are connected to other rivers only at their terminal outlets, that is, rivers with a connectivity of 1, such as Fig.12 As shown by the blue polyline, add it to the set R1 and set the level of the rivers in R1 to 1;

[0140] Step S702: remove the rivers belonging to R1 from R0 to obtain the set of remaining rivers R L_1 ,like Fig.12 As shown by the medium gray polyline, L_1 Find the river R2 whose only end is connected to other rivers, such as Fig.13 As shown by the medium cyan polyline, the level of the river in R2 is set to 2;

[0141] Step S703, in R L_1 Remove the rivers belonging to R2 and obtain the set R of remaining rivers L_2 ,like Fig.13 The gray polyline is shown in R L_2 Find the river R3 whose only end is connected to other rivers, that is, Fig.14 The middle yellow polyline sets the level of the river in R3 to 3;

[0142] Step S704, in R L_2 Remove the rivers belonging to R3 and obtain the set R of remaining rivers L_3 , at this time there is only one river left, namely Fig.14 The gray polyline in the figure is added to R4 and assigned the value of level 4. Fig.15The middle red polyline. At this point all rivers are assigned levels and the calculation stops.

[0143] In some embodiments, after step S105, the DEM integration method based on the intrinsic structure of the terrain may also include: in the i-level watershed set, if the watershed area of ​​a low-level river overlaps with the watershed area of ​​a high-level river, the watershed area of ​​the high-level river is changed to a non-overlapping area.

[0144] by Fig.15 Taking the river level shown in FIG. 1 as an example, in some embodiments, step S105 may include, but is not limited to, steps S801 to S804:

[0145] Step S801, obtain all rivers with a level not less than 1, such as Fig.16 The middle grey polyline shows that the width of the polyline represents the different levels of the river. Add the outlets of all rivers to the set P snap1 ,like Fig.16 As shown in the middle circle. Find the set P snap1 The catchment area of ​​all water outlets in the . When the catchment area of ​​a higher-level river outlet contains the catchment area of ​​a lower-level river outlet, only the non-overlapping part of the two catchments is taken as the catchment area of ​​the higher-level outlet. The set of these catchments is the set of watersheds included in level 1. Fig.16 In the data, each independent area represents a watershed.

[0146] Step S802, obtain all rivers with a level not less than 2, such as Fig.17 The middle grey polyline shows that the width of the polyline represents the different levels of the river. Add the outlets of all rivers to the set P snap2 ,like Fig.17 As shown in the middle circle. Find the set P snap2 The catchment area of ​​all water outlets in the . When the catchment area of ​​a high-level river outlet contains the catchment area of ​​a low-level river outlet, only the non-overlapping part of the two catchments is used as the catchment area of ​​the high-level outlet. The set of these catchments is the set of watersheds included in level 2. Fig.17 In the data, each independent area represents a watershed.

[0147] Step S803, obtain all rivers with a level not less than 3, such as Fig.18 The middle grey polyline shows that the width of the polyline represents the different levels of the river. Add the outlets of all rivers to the set P snap3 ,like Fig.18 As shown in the middle circle. Find the set P snap3The catchment area of ​​all the outlets in the . When the catchment area of ​​the higher-level river outlet contains the catchment area of ​​the lower-level river outlet, only the non-overlapping part of the two catchments is taken as the catchment area of ​​the higher-level outlet. The set of these catchments is the set of watersheds included in level 3. Fig.18 In the data, each independent area represents a watershed.

[0148] Step S804, obtain the river of level 4, such as Fig.19 The middle grey polyline shows the catchment area of ​​the level 4 river outlet, which is the level 4 watershed.

[0149] In some embodiments, step S106 may include but is not limited to: obtaining a ratio of the target scale to the original scale; and determining the ideal number of watersheds according to the ratio and the number of first-level watersheds.

[0150] In step S106 of some embodiments, the ideal number of watersheds is determined according to the ratio and the number of first-level watersheds, which is expressed as:

[0151]

[0152] Where M d is the target scale; M o is the original scale; N o is the number of watersheds with level 1; N d is the ideal number of watersheds.

[0153] An example is as follows: If the scale of the original DEM data is M o =1:1000, the target scale M to be obtained d The number of watersheds N with scales of 1:1500, 1:2000, 1:4000, and 1:8000, respectively, and with levels 1, 2, 3, and 4 c They are 29, 9, 3, and 1 respectively. According to the above formula, when the target scale M d When the values ​​are 1:1500, 1:2000, 1:4000, and 1:8000 respectively, N d They are 13, 7, 2 and 1 respectively.

[0154] The method for determining the ideal number of watersheds shown in the embodiment of the present application calculates the ideal number of watersheds based on the target scale and the number of watersheds at level 1, establishes the correspondence between the nested relationship of the watershed structure and the multi-scale expression of the map, and maps of any scale can be obtained from high-precision original terrain data.

[0155] After step S107 in some embodiments, the DEM integration method based on the intrinsic structure of the terrain may also include: calculating the river quantity adjustment amount based on the difference between the ideal watershed quantity and the watershed quantity of the target watershed set; obtaining a number of target rivers whose quantity is the adjusted number of rivers; and increasing or decreasing the catchment area of ​​the target river in the target watershed set.

[0156] In some embodiments, considering that adding or reducing one river will result in adding or reducing two river basins, the formula for calculating the river quantity adjustment is constructed as follows:

[0157] ΔN s =(N d -N c ) / 2

[0158] Where, ΔN s N is the river quantity adjustment; c is the number of watersheds in the target watershed set; N d is the ideal number of basins. The length of the river corresponding to the basin is used as an indicator to measure the importance of the basin. s >0, increase level l d -1, the corresponding catchment area of ​​the first ΔN longest rivers is the target basin set; when ΔN s <0, the catchment area corresponding to the first |ΔN| shortest rivers is subtracted from the target basin set.

[0159] An example is as follows: When the target scale M d =1:1500, the ideal number of watersheds N d =13, at level 1 (N d =29) and level 2 (N d =9) and is closer to level 2. Therefore, the target scale M d =1:1500, the second-level basin set is taken as the target basin set. Similarly, the target scale M can be obtained d When the scale is 1:2000, 1:4000, and 1:8000, the corresponding levels of the target basin set are 2, 3, and 4 respectively. Based on the target basin set, the number of rivers in it is adjusted so that the number of basins N in the target basin set is c and the ideal number of basins N d The same as shown in the following table:

[0160]

[0161] At the target scale M d =1:1500 as an example, calculate ΔN s=(13-9) / 2=2, so it is necessary to take the two longest rivers from the rivers of level 1, obtain their corresponding catchment areas and add them to the target basin set, and accordingly increase 4 basins.

[0162] In step S107 of some embodiments, the terrain feature points include: mountain top points, depression points, ridge lines, valley bottom lines, saddle points, ridge line nodes, and valley bottom line nodes.

[0163] The mountain top point is the grid point with the highest elevation in the watershed. Fig. 20 As shown in the figure, the elevation value of the red grid point is 3, which is the grid point with the highest elevation in the basin, that is, the top of the mountain.

[0164] The depression point is the grid point with the smallest elevation in the watershed. Fig.21 As shown in the figure, the elevation value of the blue grid point is 1, which is the grid point with the smallest elevation in the basin, that is, the depression point.

[0165] The ridgeline is a collection of boundary grids of the watershed. Fig. 22 As shown in the figure, the grids with elevation 1 in the left and right columns belong to two different watersheds, and the grids with elevation 2 in the middle column are the ridge lines.

[0166] The valley bottom line is the collection of grids where rivers in the watershed are located. Fig.23 As shown, the set of grids with an elevation value of 1 in the figure is the valley bottom line.

[0167] The saddle point is the grid point where the valley bottom line and the ridge line of the first-level river intersect. Fig.24 As shown in the figure, the blue grid represents the two valley lines starting from the central grid, and the orange grid represents the ridge line passing through the central grid. The central grid is the intersection of the valley line and the ridge line, that is, the saddle point.

[0168] A ridgeline node is a grid point on the ridgeline of the target watershed that is adjacent to at least two adjacent watersheds. Fig.25 As shown in the figure, the collection of orange grids is the ridge line, the blue grids on both sides and above the ridge line belong to three different watersheds, and the central grid is the ridge line node.

[0169] The valley bottom line node is the grid point at the intersection of two valley bottom lines in the target watershed. Fig.26 As shown in the figure, the set of blue grids is the valley bottom line. If two valley bottom lines intersect at the central grid, the central grid is the valley bottom line node.

[0170] The ridgeline nodes and valley bottom line nodes shown in the embodiments of the present application reflect the terrain features at the intersection of ridgelines and valley bottom lines, which is conducive to extracting more accurate terrain structures. The valley bottom line node is the confluence point of two rivers. At this location, the flow of the river will increase sharply. Accurately extracting this feature point is of great significance for hydrological analysis and disaster prevention. The ridgeline node is the intersection point of the ridgelines of two mountain ranges. This position is a characteristic point where the mountain terrain undergoes a sudden change. Extracting this feature is conducive to fixing the mountain shape.

[0171] It should be noted that, unlike the traditional DEM comprehensive method, the mountain top points and depression points are the extreme points in the digital elevation model; the present application extracts the mountain top points and depression points for each watershed, and the mountain top points and depression points are local features. In addition, for a watershed that is not the source of a river (i.e., does not contain a river with a level of 1), the starting point of the valley bottom line in the watershed is classified as a valley bottom line node by the present embodiment.

[0172] by Fig. 27 and Fig.28 Take the terrain feature points as an example: Fig. 27 The topographic features in the level 4 watershed are shown, including five types of topographic features: mountain tops, depressions, saddle points, ridge lines, and valley bottom lines. Fig.28 The topographic features in the three level 3 watersheds are shown, including the peak point, depression point, ridge line, valley bottom line, and ridge line intersection point. In addition, Fig.28 There is a saddle point at the source of the middle river, and there is a valley bottom intersection point in the downstream basin when two rivers intersect to form one river.

[0173] After step S108 in some embodiments, the DEM synthesis method based on the intrinsic structure of the terrain may further include: setting the level of each terrain feature point, and filtering out terrain feature points whose levels are lower than a preset level threshold; the setting of the level of each terrain feature point may include but is not limited to steps S901 to S905;

[0174] Step S901, setting the levels of the mountain top point, depression point, saddle point, valley bottom line node, and ridge line node;

[0175] Step S902, obtaining a feature point set including all terrain feature points; calculating the convex hull of the feature point set, and setting the levels of the terrain feature points corresponding to the convex hull vertices;

[0176] Step S903, constructing a triangular mesh using the terrain feature points of the set level, wherein the triangular mesh includes a plurality of triangles;

[0177] Step S904, calculating the two-dimensional plane projection of each ungraded terrain feature point; calculating the two-dimensional plane projection of each triangle; determining in turn whether the two-dimensional plane projection of each ungraded terrain feature point is within the two-dimensional plane projection of the triangle, and if so, constructing a corresponding relationship between the ungraded terrain feature point and the triangle;

[0178] Step S905, traverse all triangles, calculate the distance from the current triangle to the corresponding ungraded terrain feature point, take the point with the largest distance as the candidate point, and obtain a candidate point set; filter the candidate point set according to a preset distance threshold to obtain a salient point set; set the level of each salient point; use the salient points to update the triangular mesh to obtain the levels of the remaining ungraded terrain feature points.

[0179] by Fig. 27 Taking the terrain feature points shown in FIG. 1 as an example, in some embodiments, the steps of setting the levels of the terrain feature points may include, but are not limited to, steps S1001 to S1006;

[0180] Step S1001: Fig. 27 The terrain feature points in are classified into grades 1 to 5, and the mountain top points, depression points, saddle points, valley bottom line nodes, and ridge line nodes are assigned grades 1 to 5 respectively. A set U is established, and the grid points included in the valley bottom line and ridge line are added to the set U as feature points without grade setting.

[0181] Step S1002, find the convex hull of the point set consisting of all terrain feature points, and assign the vertices of the convex hull to level 6.

[0182] Step S1003, set the current level L = 7. Use the terrain feature points with the set level (such as Fig.29 The red dots shown here construct the Delaunay triangulation mesh T L (like Fig.29 The red line in the figure shows the result. The two-dimensional plane projection of the feature points in the set U is based on whether it is on the Delaunay triangulation mesh T. L In the two-dimensional plane projection of the middle triangle, the corresponding relationship between the terrain feature points and the triangle is established.

[0183] Step S1004, traverse the Del aunay triangular mesh T L For all triangles in , perform the following operations: For the terrain feature point corresponding to triangle i (such as Fig.29 ), calculate the distances from these points to the two-dimensional plane where triangle i is located, and record the terrain feature point with the largest distance as The maximum distance is The terrain feature points of triangle i are and the maximum distance value Put them into candidate point set P and set D respectively. In this example, the distances from the terrain feature points in set P to the corresponding triangle surface are d A =0.352; d B =0.640; d C =13.9; d D =0.2; d E =13.5; d F =12.8; d G =

[0184] 0.2;d H =12.7; d I =11.0;d J =4.8; d K =1.4.

[0185] Step S1005, find the maximum value d in set D max In this example, d max =d C =13.9. To ensure that the significance of terrain feature points of the same level is roughly similar, d max The half of is the distance threshold; the candidate point set P is screened according to the distance threshold. The specific screening method is: traverse each value in the set D If satisfied Then the distance The corresponding terrain feature points are added to the salient point set P F , and delete the point from the set U at the same time, and use the terrain feature point as the new vertex to form three new triangles with the first and last vertices of the three sides of the original triangle, and update the De la aunay triangular mesh; if it does not meet Then the point remains in the set U. Traverse all After the value is obtained, jump to the next step. F The point in Fig.30 Points C, E, F, H, and I shown are the terrain feature points of the current level L.

[0186] Step S1006, adding 1 to the level L, and repeatedly executing the calculation steps of step S1004 to step S1005 until all the terrain feature points are ranked, that is, when the set U is an empty set, the calculation ends.

[0187] In some embodiments, step S109 may include, but is not limited to: interpolating the feature extraction results (such as sparse matrix feature points) obtained in step S108 using the Kriging method to obtain a digital elevation model.

[0188] Taking a river basin in Yunnan as an example, the DEM synthesis method based on the intrinsic structure of the terrain was implemented, and multiple digital elevation models of different scales were obtained. Fig.31 As shown, it can be seen that in the comprehensive results of different levels, the terrains of different levels are preserved, and the comprehensive results of each level reflect the inherent hierarchical structure of the terrain.

[0189] The embodiment of the present application also provides a DEM synthesis device based on the intrinsic structure of the terrain, which can implement the above-mentioned DEM synthesis method based on the intrinsic structure of the terrain, and the device includes:

[0190] A data acquisition module is used to obtain original terrain elevation data;

[0191] A hydrological network identification module, used for identifying a hydrological network in the original terrain elevation data, wherein the hydrological network includes a plurality of river sections;

[0192] The river extraction module is used to iteratively identify the mainstream by taking the hydrological network as the identification object, and obtain at least one identification result in each round of mainstream identification, and the identification result includes a river and a plurality of sub-hydrological networks; each of the sub-hydrological networks is used as the identification object of the next round of mainstream identification until the iteration stop condition is reached; after the iteration is completed, a river set is obtained, and the river set includes a plurality of the rivers and the topological relationship between the rivers;

[0193] The watershed construction module is used to extract the catchment area of ​​each river as the i-level watershed for rivers with a river level not less than i (i = 1, 2...), and obtain the i-level watershed set;

[0194] The model reconstruction module is used to obtain the ideal number of watersheds; select the n-level watershed set whose watershed number is closest to the ideal number of watersheds as the target watershed set; extract terrain feature points from the target watershed set; and establish a digital elevation model using the extracted terrain feature points.

[0195] The specific implementation of the device is basically the same as the specific implementation of the above-mentioned DEM integration method based on the intrinsic structure of the terrain, and will not be repeated here.

[0196] The embodiment of the present application also provides an electronic device, the electronic device includes a memory and a processor, the memory stores a computer program, and the processor implements the above-mentioned DEM synthesis method based on the intrinsic structure of the terrain when executing the computer program. The electronic device can be any intelligent terminal including a tablet computer, a car computer, etc.

[0197] The embodiment of the present application also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the above-mentioned DEM synthesis method based on the intrinsic structure of the terrain is implemented.

[0198] The memory, as a non-transient computer-readable storage medium, can be used to store non-transient software programs and non-transient computer executable programs. In addition, the memory may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some embodiments, the memory may optionally include a memory remotely disposed relative to the processor, and these remote memories may be connected to the processor via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0199] The DEM integration method, device, electronic device and storage medium based on the intrinsic structure of terrain provided in the embodiments of the present application iteratively divide the hydrological network into sub-hydrological networks for mainstream identification, extract the mainstreams of different scale areas in the hydrological network as rivers, and the obtained river set reflects the vitality structure of the hydrological network; then the rivers are classified according to the topological relationship of the rivers, and a multi-level basin set is constructed based on the multi-level rivers, and the high-level basin set is nested in the low-level basin set, which fully considers the interaction between the river and the surface morphology, and extracts the nested substructure of the basin based on the vitality structure of the hydrological network, and clarifies the inherent hierarchical relationship between the basins; then the corresponding level target basin set is selected according to the ideal number of basins to extract terrain feature points to reconstruct the digital elevation model, and the surface morphological characteristics are accurately extracted based on the vitality structure of the hydrological network, which can simplify the DEM terrain while retaining the original data characteristics as much as possible.

[0200] The embodiments described in the embodiments of the present application are intended to more clearly illustrate the technical solutions of the embodiments of the present application and do not constitute a limitation on the technical solutions provided in the embodiments of the present application. Those skilled in the art will appreciate that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0201] Those skilled in the art will appreciate that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than shown in the figures, or a combination of certain steps, or different steps.

Claims

1. DEM synthesis method based on the intrinsic structure of terrain, characterized by: The method comprises: Get the original terrain elevation data; identifying a hydrological network in the original terrain elevation data, the hydrological network comprising a plurality of river segments; Iteratively perform mainstream identification on the hydrological network as the identification object, and obtain at least one identification result in each round of mainstream identification, wherein the identification result includes a river and a plurality of sub-hydrological networks; each of the sub-hydrological networks is used as the identification object of the next round of mainstream identification until an iteration stop condition is reached; after the iteration is completed, a river set is obtained, wherein the river set includes a plurality of the rivers and the topological relationship between the rivers; According to the topological relationship, setting a river level for each river; For rivers with a river grade not less than i (i = 1, 2, ...), the catchment area of ​​each river is extracted as the i-level basin, and the i-level basin set is obtained; Get the ideal number of watersheds; Selecting an n-level watershed set whose watershed number is closest to the ideal watershed number as the target watershed set; Extract terrain feature points from the target watershed set; The digital elevation model is established using the extracted terrain feature points.

2. The method according to claim 1, characterized in that: The method further includes performing data preprocessing on the original terrain elevation data; the data preprocessing on the original terrain elevation data includes: Extract depressions from the original terrain elevation data; calculate the depression depth of each depression to obtain a depression depth set; use the head-tail segmentation method to segment the depression depth set into a head set and a tail set; select the depression corresponding to the tail set as an unnaturally formed depression and fill the unnaturally formed depression.

3. The method according to claim 1, characterized in that The identifying of the hydrological network in the original terrain elevation data comprises: Calculate the water flow direction of each grid in the original terrain elevation data; traverse each grid according to the water flow direction, calculate the cumulative flow of each grid, and obtain a cumulative flow set; use the head-tail segmentation method to iteratively segment the cumulative flow set into a head set and a tail set until the iteration stop condition is met; determine the river section threshold according to the average value of the tail set; perform vectorization operation on the grid whose cumulative flow value is greater than the river section threshold, and obtain a directed polyline set, each directed polyline is a river section.

4. The method according to claim 1, characterized in that The mainstream identification includes: The longest river path in the identified object is extracted as the initial mainstream; the initial mainstream is removed from the identified object, and the remaining river sections are divided into multiple sub-hydrological networks according to the connection relationship; the longest river path in each sub-hydrological network is extracted as the alternative mainstream; the importance of each alternative mainstream relative to the initial mainstream is calculated based on the path length and path angle; if the maximum importance is a positive value, the alternative mainstream corresponding to the maximum importance is output as the river; otherwise, the initial mainstream is output as the river.

5. The method according to claim 1, characterized in that The step of setting a river level for each river according to the topological relationship includes: Set the river that is connected to other rivers only at the terminal outlet as a level 1 river; Remove j (j=1, 2, ...) level rivers, and set the remaining rivers that are connected to other rivers only at their terminal outlets as j+1 level rivers, with j increasing by 1. Repeat this step until all rivers are assigned levels.

6. The method according to claim 1, characterized in that Also includes: In the i-level basin set, if the catchment area of ​​a low-level river overlaps with the catchment area of ​​a high-level river, the catchment area of ​​the high-level river is changed to a non-overlapping area.

7. The method according to claim 1, characterized in that The obtaining of the ideal number of watersheds includes: obtaining a ratio of a target scale to an original scale; and determining the ideal number of watersheds according to the ratio and the number of first-level watersheds.

8. The method according to claim 1, characterized in that: Also includes: Calculating the river quantity adjustment amount according to the difference between the ideal watershed quantity and the watershed quantity of the target watershed set; Acquire a number of target rivers whose number is the adjusted number of the rivers; and increase or decrease the catchment area of ​​the target rivers in the target river basin set.

9. The method according to claim 1, characterized in that: The terrain feature points include: mountain top points, depression points, ridge lines, valley bottom lines, saddle points, ridge line nodes and valley bottom line nodes; the ridge line nodes are grid points in the ridge line of the watershed that are adjacent to at least two adjacent watersheds; the valley bottom line nodes are grid points at the intersection of two valley bottom lines in the watershed.

10. The method according to claim 9, characterized in that Also includes: Setting the level of each terrain feature point, and filtering out terrain feature points whose level is lower than a preset level threshold; the setting of the level of each terrain feature point includes: Set the levels of the mountain top, depression, saddle, valley bottom, and ridgeline nodes; Obtain a feature point set including all terrain feature points; calculate the convex hull of the feature point set, and set the levels of the terrain feature points corresponding to the convex hull vertices; Constructing a triangular mesh using the terrain feature points of the set level, wherein the triangular mesh includes a plurality of triangles; Calculate the two-dimensional plane projection of each ungraded terrain feature point; calculate the two-dimensional plane projection of each triangle; determine in turn whether the two-dimensional plane projection of each ungraded terrain feature point is within the two-dimensional plane projection of the triangle, and if it is within the two-dimensional plane projection of the triangle, then construct a corresponding relationship between the ungraded terrain feature point and the triangle; Traverse all triangles, calculate the distance from the current triangle to the corresponding ungraded terrain feature point, take the terrain feature point with the largest distance as the candidate point, and obtain a candidate point set; filter the candidate point set according to the preset distance threshold to obtain a significant point set; The level of each salient point is set; and the triangular mesh is updated using the salient point set to obtain the levels of the remaining terrain feature points that have not been set.

11. A DEM synthesis device based on the intrinsic structure of the terrain, characterized by: The device comprises: A data acquisition module is used to obtain original terrain elevation data; A hydrological network identification module, used for identifying a hydrological network in the original terrain elevation data, wherein the hydrological network includes a plurality of river sections; The river extraction module is used to iteratively identify the mainstream by taking the hydrological network as the identification object, and obtain at least one identification result in each round of mainstream identification, and the identification result includes a river and a plurality of sub-hydrological networks; each of the sub-hydrological networks is used as the identification object of the next round of mainstream identification until the iteration stop condition is reached; after the iteration is completed, a river set is obtained, and the river set includes a plurality of the rivers and the topological relationship between the rivers; The watershed construction module is used to extract the catchment area of ​​each river as the i-level watershed for rivers with a river level not less than i (i = 1, 2...), and obtain the i-level watershed set; The model reconstruction module is used to obtain the ideal number of watersheds; select the n-level watershed set whose watershed number is closest to the ideal number of watersheds as the target watershed set; extract terrain feature points from the target watershed set; and establish a digital elevation model using the extracted terrain feature points.

12. An electronic device, characterized in that: The electronic device comprises a memory and a processor, the memory stores a computer program, and the processor implements the method according to any one of claims 1 to 10 when executing the computer program.

13. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 10 is implemented.

Images