A water system extraction method based on digital elevation model DEM

Abstract

The present invention discloses a water system extraction method based on a digital elevation model (DEM). The field of water system extraction methods related to digital elevation models belongs to the field of geoscience. The water system extraction method based on a digital elevation model (DEM) comprises the following steps: step (1): pre-processing the data to be operated, logging into a geospatial data cloud network platform to cut and download the selected area data, mosaicking the obtained area data, and adding administrative district boundaries as references; step (2): using ArcGIS's own system toolbar to fill the original DEM data, extracting the flow direction of the filled depression, using the flow direction as input, outputting flow data, and calculating the flow direction accumulation grid. Based on the digital elevation model (DEM), the present invention realizes the extraction of rivers, water outlets and watersheds by simulating the process of surface water forming runoff, which is convenient and fast, and the extraction of small watersheds is more accurate and clear.

Description

Technical Field

[0001] The invention relates to a water system extraction method of a digital elevation model, which belongs to the field of geoscience, and specifically relates to a water system extraction method based on a digital elevation model DEM. Background Art

[0002] Geographic Information System (GIS) is widely used in different fields. Its spatial analysis function has mature theories and models in hydrological analysis, which greatly facilitates the extraction of river systems. Water system analysis is one of the important contents in landform research. The distribution characteristics of water systems are closely related to climate and topography. Therefore, through the study of water systems, the topography and landforms in the study area can be well analyzed. With the popularization of the Internet, various DEM data can also be downloaded from the Internet. Although the accuracy is relatively low, the data is easy to obtain and can meet many application needs. In China, relevant DEM digital elevation models can be intercepted and downloaded on the Geospatial Data Cloud Network Platform (www.gscloud.cn / search). There are SRTMDEMUTM90M resolution digital elevation data, GDEMV30M resolution digital elevation data, etc. It is convenient and fast, and has become one of the main sources of data for many scientific researchers.

[0003] Surface hydrological analysis models are used to study various natural phenomena related to surface water flow, such as flood levels and flooding, or to delineate areas affected by pollution sources, and to predict the consequences of changing the topography of a certain area on the entire area. Rapid and effective acquisition of water system distribution characteristics is also of great significance for achieving effective allocation of water resources, comprehensive basin planning, and many other fields. However, existing water system extraction methods cannot intuitively display the flow path and flow size of rivers. Summary of the invention

[0004] The purpose of the present invention is to provide a water system extraction method based on a digital elevation model (DEM), to provide a detailed display of the river network distribution and the extraction of watershed characteristics in the study area, and to improve the efficiency of extraction and the accuracy of the results by comparing with the watershed map measured in the field. At the same time, ArcSCENE is used to perform three-dimensional stereoscopic operations on the topography to make the relationship between the river network and the terrain elevation clearer and more intuitive.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A water system extraction method based on a digital elevation model (DEM), comprising the following steps:

[0007] Step (1): pre-process the data to be operated, log in to the geospatial data cloud network platform to cut and download the selected area data, mosaic the obtained area data, and add the administrative area boundary as a reference;

[0008] Step (2): Use ArcGIS's built-in system toolbar to fill the original DEM data, extract the flow direction of the filled depression, use the flow direction as input, output flow data, and calculate the flow direction accumulation grid;

[0009] Step (3): setting a confluence threshold based on the data of the flow direction and the flow rate, generating a river network, connecting the discrete point data into image points, and then connecting them into lines to form a river chain, classifying the size of the river according to the flow rate data, and using vectors to represent the classification data of the river;

[0010] Step (4): extracting the watershed based on the flow direction and the flow rate, drawing pouring points, capturing pouring points, and dividing the watershed range according to the watershed;

[0011] Step (5): Display the river network data and the DEM data in a three-dimensional form.

[0012] Furthermore, the distribution characteristics of the water system in the study area are studied and the range of the watershed is extracted, and the extracted distribution characteristics and the range of the watershed are compared with the watershed map measured on the spot.

[0013] Furthermore, in the step (3), a confluence threshold is set based on the flow direction and flow data, and a formula is used to remove redundant small rivers.

[0014] Furthermore, in the step (4), a new point element is created to simply mark the pouring point; the drawn pouring point is systematically captured to eliminate errors; and the watershed basin is extracted.

[0015] Furthermore, in the step (5), ArcScene software is used to display the river network data and DEM data in a three-dimensional form.

[0016] The ArcGIS-based water system extraction method of the present invention comprises:

[0017] 1. Data preprocessing: Log in to the geospatial data cloud network platform to cut and download the data of the selected area, splice the obtained data, and add the administrative district boundaries as a reference.

[0018] 2. Hydrological Analysis

[0019] (1) Depression filling: The original DEM data is processed through tools to fill depressions so that water can flow smoothly to the edges of the regional terrain.

[0020] (2) Flow direction determination: Use tools to extract the flow direction of the filled depression and determine the direction of the water flow.

[0021] (3) Calculate the cumulative runoff value: Use the tool to take the flow direction as input, output the flow data, and calculate the flow direction accumulation grid.

[0022] 3. Constructing the River Network

[0023] (1) River network generation: The confluence threshold is set based on the flow direction and flow data, and a formula is used to remove redundant small rivers so that the rivers in subsequent operations appear less cluttered.

[0024] (2) River linking: The discrete point data obtained in the previous step are connected into image points, and then connected into lines to form a river chain.

[0025] (3) River network classification: Classify the size of rivers.

[0026] (4) River network vectorization: The river network classification data can be expressed in vector form to more clearly express the lines of the rivers and perform systematic symbolization at the same time.

[0027] 4. Watershed Extraction

[0028] (1) Pour point: Based on the flow direction and flow of rivers in the river network, new point features are created to simply mark the pour points.

[0029] (2) Capturing the pouring point: The pouring point obtained in the previous step has certain errors, and a systematic capture is required to eliminate the errors.

[0030] (3) Watershed: A watershed in GIS is a large river basin with multiple small watersheds nested in it.

[0031] 5. 3D Terrain Modeling

[0032] Display river network data and DEM data in three-dimensional form.

[0033] Beneficial effects of the present invention:

[0034] The present invention uses the hydrological analysis function of ArcGIS software to automatically classify river networks and watersheds on the basis of the digital elevation model DEM, and realizes the extraction of rivers, water outlets and watersheds by simulating the process of surface water forming runoff. It is convenient and fast, and the extraction of small watersheds is more accurate and clear. In ArcScene software, the river network data is attached to the DEM elevation, and the ups and downs are clear, so that the flow path and flow size of the river can be better understood. The water system extraction method based on the digital elevation model DEM saves energy and time, is quantitatively accurate, and conforms to the water system distribution characteristics caused by the real topography. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below in conjunction with the accompanying drawings.

[0036] Figure 1 It is a model construction diagram of the present invention;

[0037] Figure 2 It is a schematic diagram of water flow direction value;

[0038] Figure 3 This is the result of filling the depression in the example;

[0039] Figure 4 It is the result map of the watershed in the example; DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figures 1 to 4 As shown, a water system extraction method based on a digital elevation model DEM comprises the following steps:

[0042] Step (1): pre-process the data to be operated, log in to the geospatial data cloud network platform to cut and download the selected area data, mosaic the obtained area data, and add the administrative area boundary as a reference;

[0043] Step (2): Use ArcGIS's built-in system toolbar to fill the original DEM data, extract the flow direction of the filled depression, use the flow direction as input, output flow data, and calculate the flow direction accumulation grid;

[0044] Step (3): setting a confluence threshold based on the data of the flow direction and the flow rate, generating a river network, connecting the discrete point data into image points, and then connecting them into lines to form a river chain, classifying the size of the river according to the flow rate data, and using vectors to represent the classification data of the river;

[0045] Step (4): extracting the watershed based on the flow direction and the flow rate, drawing pouring points, capturing pouring points, and dividing the watershed range according to the watershed;

[0046] Step (5): Display the river network data and the DEM data in a three-dimensional form.

[0047] Furthermore, the step (1) specifically includes the following detailed steps:

[0048] Step (1-1): Download the required 30M spatial resolution DEM data from the Geospatial Data Cloud, decompress it to get tif data, and add it to the ArcGIS content list. Specific operation: Open the toolbox and execute the command: Data Management Tools - Raster - Raster Dataset - Mosaic to New Raster, and set the input raster, save path, spatial reference, pixel type and number of bands in the dialog box.

[0049] Step (1-2): Add China State Boundaries.shp (polygon) and execute the command: Right-click China State Boundaries.shp and select Properties - Define Query - Query Builder - Enter Formula - OK.

[0050] Furthermore, the step (2) specifically includes the following detailed steps:

[0051] Step (2-1): Depression filling. Usually, DEM is a relatively smooth terrain surface model. However, due to differences in some real terrain features, such as the presence of ponds, there are some sunken areas. The existence of these areas will cause errors in the calculation of river flow direction. Therefore, before extracting the river network, the original DEM data must be depressurized to make the terrain flat and obtain depression-free DEM raster data. By default, ArcGIS automatically raises the grid cells in the depression to the elevation of the surrounding grid cells to perform depression filling. Specific operation: Open the toolbox and execute the command: SpatialAnalyst Tools - Hydrological Analysis - Depression Filling, and set the input surface raster data and output surface raster data in the dialog box.

[0052] Step (2-2): For a grid, flow direction refers to the direction in which water flows when it leaves the grid. In ArcGIS, the single flow method D8 is generally used, which assumes that the water flow in each cell can only flow in eight directions and all flow into the eight adjacent cells. The grid direction code is as follows: Figure 2 Specific operation: Open the toolbox, execute the command: SpatialAnalyst tool - Hydrological Analysis - Flow Direction, and set the save path of the input surface raster data and the output flow direction raster data in the dialog box.

[0053] Step (2-3): Calculate the cumulative value of the confluence. The flow rate is to calculate the total number of grids that the upstream water path corresponding to any grid cell flows through, that is, how many grids of water flow converge to a certain point. Specific operation: Open the toolbox and execute the command: SpatialAnalyst Tools - Hydrological Analysis - Flow Rate, and set the save path of the input flow direction grid data and the input storage grid data in the dialog box.

[0054] Furthermore, the step (3) specifically includes the following detailed steps:

[0055] Step (3-1): River network generation. When the water flow reaches a certain flow value, it forms surface runoff. When the runoff reaches a certain value, it becomes a river in the conventional sense. Therefore, a threshold can be determined according to the different climate, topography and other factors in different study areas. When the flow exceeds this threshold, it can be determined that the grid point can be used for the calculation range of the water system division, and the river network is constructed by formula calculation and classification. The larger the threshold, the fewer grids that exceed the threshold, and the fewer rivers. The VALUE value is set through the conditional function to remove the value with too little flow, making subsequent operations simpler and less messy. Specific operation: Open the toolbox and execute the command: SpatialAnalyst tool-conditional analysis-conditional function. Enter the formula in the dialog box to set the threshold and obtain the river network calculation result.

[0056] Step (3-2): River linking, connect the obtained discrete point data into image points, determine the rivers of various levels according to the flow direction, and finally connect them into lines to form a river chain. Specific operation: Open the toolbox and execute the command: SpatialAnalyst tool - Hydrological Analysis - River Linking, enter the river raster data and flow direction in the dialog box, set the output raster path, and obtain the river network link result.

[0057] Step (3-3): River network classification. There are two methods for river network classification in ArcGIS - Strahler and Shreve. The two methods are similar but different. The similarity is that both define the water system without tributaries as level 1. When two water systems of the same level merge, the level increases. However, the difference is that the Strahler classification method increases the level by 1 level. If the levels are different, they are counted as the highest level river level, while the increase in the level of the Shreve classification method is to directly add the level number. Therefore, in comparison, the Strahler classification method has a lower level, and the present invention adopts this classification method. Specific operation: Open the toolbox and execute the command: SpatialAnalyst tool - Hydrological analysis - River network classification, enter the river raster data and flow direction data in the dialog box, and set the output raster save path and classification method.

[0058] Step (3-4): Vectorize the river network, convert the river network classification raster data into vector linear data, better mark the rivers, and perform finishing output. Specific operation: Open the toolbox and execute the command: Spatial Analyst Tools - Hydrological Analysis - Raster River Network Vectorization, enter the river raster data and flow direction data in the dialog box, set the save path of the output elements, and obtain the vectorized river network results.

[0059] Furthermore, the step (4) specifically includes the following detailed steps:

[0060] Step (4-1): Draw the pour point. The pour point data refers to the outlet of the river, that is, the point where the flow in the entire upstream basin is the maximum, and where the tributaries converge to the runoff. This can be operated through the river network obtained in the above steps. Specific operations: Create a new point feature dataset, set the coordinate grid to WGS1984, select the editor to start editing, draw the pour point where the confluence value is the largest, save the edited content, and end the editing.

[0061] Step (4-2): Capture the pour point. The pour point drawn in the previous step has errors and needs to be recalibrated, that is, find the closest maximum flow rate among the drawn pour points to use as the pour point. Specific operation: Open the toolbox and execute the command: SpatialAnalyst Tools - Hydrological Analysis - Capture Pour Point. Enter the pour point data and flow data in the dialog box, set the save path and capture distance of the output feature, and obtain the captured pour point result.

[0062] Step (4-3): Watershed, determine the spatial scope of the river based on the river, flow direction and outlet, extract the catchment basin, use the pour point data for input, and obtain the catchment area corresponding to the pour point. Specific operation: Open the toolbox and execute the command: SpatialAnalyst tool - Hydrological Analysis - Watershed, enter the flow direction and pour point data in the dialog box, set the save path of the output raster, and obtain the extracted basin scope.

[0063] Furthermore, the step (5) specifically includes the following detailed steps:

[0064] Step (5-1): Open ArcScene, use the projection and transformation tools to convert the DEM data into a projected coordinate system and then display it in the 3D layer. Specific operation: Open the toolbox, execute the command: Data Management Tools - Projection and Transformation - Define Projection, and set the input grid and coordinate system in the dialog box.

[0065] Step (5-2): Import the projected coordinate system, select the base height in the properties, set the custom surface floating, and make the plane Figure 3 D becomes three-dimensional and sets the color of the symbol system.

[0066] Step (5-3): Import river network data, adjust the river line width, color, etc., select the basic height in the properties, and set the custom surface floating to make the river network emerge in the three-dimensional elevation fluctuations.

[0067] The specific operations are as follows:

[0068] Perform the following steps according to step (1):

[0069] Download and cut the DEM data of the target city with a spatial resolution of 30M through the geospatial data cloud, decompress it to obtain tif data, and add it to the ArcGIS content list.

[0070] Open the toolbox and execute the command: Data Management Tools - Raster - Raster Dataset - Mosaic to New Raster - Input Raster: All DEM data of the target city, Output location - Folder "mubiaochengshi", Name of the raster dataset with extension - mubiaochengshi_dem, Spatial reference of raster data: WGS1984, Pixel type - 16_BIT_UNSIGNED, Number of bands - 1, Other defaults - OK, and the mosaicked mubiaochengshi_dem is obtained. Then add China State Boundary.shp (surface) and execute the command: China Provincial Administrative Region.shp right-click Properties - Define Query - Query Builder - Enter the formula ""NAME"LIKE'Target City'" - OK, and the administrative boundary of the target city is obtained.

[0071] Follow step (2):

[0072] Filling depressions: Open the toolbox and execute the command: SpatialAnalyst Tools – Hydrological Analysis – Fill depressions – Input surface grid data: mubiaochengshi_clip, Output surface grid: fill – OK, and obtain the elevation data fill after filling the depression. Determine flow direction: Open the toolbox and execute the command: SpatialAnalyst Tools – Hydrological Analysis – Flow Direction – Input surface grid data: fill, Output flow direction grid data: direction, and leave the rest as default – OK, and obtain the flow direction data direction. Calculate flow: Open the toolbox and execute the command: SpatialAnalyst Tools – Hydrological Analysis – Flow – Input flow direction grid data: direction, Output accumulation grid data: accumulation, Select output data type: FLOAT – OK, and obtain the cumulative flow data accumulation.

[0073] Follow step (3):

[0074] River network generation: Open the toolbox and execute the command: SpatialAnalyst tool - Conditional analysis - Conditional function - Input conditional grid data: accumulation, embed "VALUE>=20000" in the expression, input the grid data taken when the condition is true: accumulation, output grid: con_20000 - OK, and get the river network calculation result con_20000. River link: Open the toolbox and execute the command: SpatialAnalyst tool - Hydrological analysis - River link - Input river grid data: con_20000, input flow direction grid data: direction, output grid: link - OK, and get the river network link result link. River network classification: Open the toolbox and execute the command: SpatialAnalyst tool - Hydrological analysis - River network classification - Input river grid data: link, input flow direction data: direction, output grid: class, select STRAHLER for river network classification method - OK, and get the classified result class. River network vectorization Open the toolbox and execute the command: SpatialAnalyst tool - Hydrological Analysis - Raster River Network Vectorization - Input river raster data: class, input flow direction data: direction, output polyline feature: stream, check Simplify Polyline - OK, and get the vectorized river network result stream. Design the line width, color, etc. of its river level in accordance with the system to make the river level distinction more obvious.

[0075] Follow step (4):

[0076] Draw pour points: Create a new point feature dataset pour_point, set the coordinate grid to WGS1984, select the editor to start editing, draw the pour point where the confluence value is the largest, save the edited content, end editing, and get the pour point pour_point. Capture pour points: Open the toolbox and execute the command: SpatialAnalyst Tools - Hydrological Analysis - Capture Pour Points - Input feature pour point data: pour_point, pour point field: OBJECTID, input accumulation grid data: accumulation, output grid: pour, capture distance: 0.1 - OK, get the captured pour point result pour. Watershed: Open the toolbox and execute the command: SpatialAnalyst Tools - Hydrological Analysis - Watershed, input flow direction grid data: direction, input feature pour point data: pour, pour point field: Value, output grid: watershed - OK, get the extracted watershed range watershed, and then symbolize it.

[0077] Follow step (5):

[0078] Open ArcScene, use the projection and transformation tools to convert the mubiaochengshi_dem data into a projected coordinate system and then display it in a three-dimensional layer. Specific operations: Open the toolbox and execute the command: DataManagement Tools - Projection and Transformation - Define Projection - Input Dataset: mubiaochengshi_dem, Coordinate System: WGS_1984_UTM_Zone_49N - OK, and get the projected dem_touying. Reopen ArcScene, import the projected dem_touying, select the basic height in the properties, set it to float on the custom surface, set the custom value to 15, and set the color of the symbol system. Import the river network data stream, modify the line width, color, etc. of the river, select the basic height in the properties, set it to float on the custom surface, and set the custom value to 15, so that the river network emerges in the three-dimensional elevation fluctuations.

[0079] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0080] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A water system extraction method based on digital elevation model DEM, characterized in that: The following steps are involved: Step (1): pre-process the data to be operated, log in to the geospatial data cloud network platform to cut and download the selected area data, mosaic the obtained area data, and add the administrative area boundary as a reference; Step (2): Use ArcGIS's built-in system toolbar to fill the original DEM data, extract the flow direction of the filled depression, use the flow direction as input, output flow data, and calculate the flow direction accumulation grid; Step (3): setting a confluence threshold based on the data of the flow direction and the flow rate, generating a river network, connecting the discrete point data into image points, and then connecting them into lines to form a river chain, classifying the size of the river according to the flow rate data, and using vectors to represent the classification data of the river; Step (4): extracting the watershed based on the flow direction and the flow rate, drawing pouring points, capturing pouring points, and dividing the watershed range according to the watershed; Step (5): Display the river network data and the DEM data in a three-dimensional form.

2. According to the water system extraction method based on the digital elevation model DEM described in claim 1, its characteristics are that the water system distribution characteristics of the study area are studied and the basin range is extracted, and the extracted distribution characteristics and the basin range are compared with the basin map measured in the field.

3. According to the water system extraction method based on the digital elevation model (DEM) described in claim 1, its characteristic is that in the step (3), a confluence threshold is set based on flow direction and flow data, and a formula is used to remove redundant small rivers.

4. According to the method for extracting water systems based on a digital elevation model (DEM) as described in claim 1, its characteristics are: in the step (4), a new point element is created to simply mark the pouring point; the drawn pouring point is systematically captured to eliminate errors; and the catchment area basin is extracted.

5. The method for extracting water systems based on a digital elevation model (DEM) according to claim 1 is characterized in that in the step (5), the river network data and the DEM data are displayed in a three-dimensional form using ArcScene software.

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