Rapid extraction method for any global river channel parameters

Abstract

The invention relates to the technical field of riverway parameter extraction, in particular to a rapid extraction method for any global riverway parameters, which can realize rapid extraction of any target river reach parameters in a global range, greatly reduce the cost of manual intervention, improve the speed and accuracy of riverway parameter extraction, and improve the accuracy of riverway parameter extraction. And more efficient and accurate technical support is provided for hydrological analysis and water resource management. According to the method, a global DEM data set, a flow direction raster data set and a cumulative flow raster data set are prepared in advance, and the method for rapidly extracting the flowing path of any river reach based on flow direction raster and cumulative flow raster data is provided. And the water flow path of the target river reach can be rapidly extracted and vectorized rendering is carried out, so that second-level extraction of the river length and the gradient of any global river reach is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of river channel parameter extraction, and particularly relates to a method for rapidly extracting global arbitrary river channel parameters. Background Art

[0002] River channel parameters, as important indicators for describing river morphology and hydrodynamic characteristics, are not only the basic data for hydrological analysis and water resources scheduling, but also provide a scientific basis for river ecological restoration, shipping planning, and disaster prevention and warning. Accurate river channel data can support the construction of flood routing models, the optimization of reservoir operation, and the assessment of ecological flow. Especially when dealing with flood disasters caused by extreme climate, quickly obtaining dynamic river section parameters is crucial for emergency decision-making.

[0003] Traditional methods for extracting river channel parameters mainly rely on manual field measurements. Restricted by complex geographical environments and extreme climate conditions, the manual measurement method is inefficient and difficult to achieve large-scale dynamic acquisition. With the rapid development of remote sensing technology, digital elevation model (DEM) data, and geographic information system (GIS) technology, new technological breakthroughs have emerged in the extraction of river channel parameters. For example, using remote sensing images to collect the planar morphology and elevation information of river channels, and then obtaining the characteristic parameters of river channels. This method has improved the efficiency of manually collecting river channel information to a certain extent, but requires professional image processing and analysis technologies, with high technical costs, and cannot achieve the rapid extraction of global arbitrary river channel parameters. In addition, using DEM data combined with GIS technology to extract river channel data requires steps such as clipping, filling depressions, flow direction analysis, flow calculation, and river network generation for the DEM according to the research area. The operation is cumbersome and mainly used for the extraction of complete river networks, lacking the function of quickly extracting parameters for user-specified river sections. Summary of the Invention

[0004] In view of this, the present invention proposes a method for rapidly extracting global arbitrary river channel parameters, which can achieve the rapid extraction of parameters for any target river section globally, greatly reducing the cost of manual intervention, improving the speed and accuracy of river channel parameter extraction, and providing more efficient and accurate technical support for hydrological analysis and water resources management.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A method for rapidly extracting global arbitrary river channel parameters, comprising the following steps: Preprocessing step: Correcting global digital elevation model data and generating a global flow direction raster dataset and a cumulative flow raster dataset; Path tracing steps: Input the longitude and latitude coordinates of the starting point of the global target river section. Utilize the geographical information attributes of the global flow direction raster dataset and the cumulative flow raster dataset to convert the longitude and latitude coordinates of the starting point into the pixel coordinates of the starting point. Starting from the pixel coordinates of the starting point, in accordance with the flow law of the flow direction raster data, iterate through the pixel values of the flow direction raster and the cumulative flow raster by iterative calculation. Record the flow direction value and the cumulative flow value of the current point in each iteration, and store the pixel coordinates obtained at each step. Stop traversing when the cumulative flow value is equal to zero to obtain the set of pixel coordinates of the river path from the starting point of the river section to the estuary. Input the longitude and latitude coordinates of the ending point downstream of the target river section, and repeat the above conversion and iterative tracing process to obtain the set of pixel coordinates of the river path from the ending point of this river section to the estuary. River section extraction steps: Convert the set of pixel coordinates from the starting point to the estuary and the set of pixel coordinates from the ending point to the estuary into the corresponding sets of longitude and latitude coordinates respectively. Based on the relationship that the longitude and latitude coordinates of the starting point and the ending point are located upstream and downstream of the target river section, on the basis of the set of longitude and latitude coordinates from the starting point to the estuary, deduct all elements in the set of longitude and latitude coordinates from the ending point to the estuary except the ending point coordinates to obtain the set of longitude and latitude coordinates of the target river section containing the starting point and the ending point. The set of pixel coordinates corresponding to this set of longitude and latitude coordinates of the target river section is the set of pixel coordinates of the target river section. Parameter calculation steps: Extract the elevation sequence from the digital elevation model data based on the set of pixel coordinates of the target river section. Obtain the river length parameter by cumulatively adding the distances between adjacent points point by point using the spherical distance algorithm, and calculate the river slope parameter by using the segmented weighted method.

[0006] Among them, the preprocessing step includes using the water system data of high-resolution remote sensing images to correct the original digital elevation model to generate corrected elevation data, and performing filling depression calculations on this data to generate a flow direction raster dataset and a cumulative flow raster dataset.

[0007] Among them, in the path tracing step, the determination condition that the cumulative flow value is 0 corresponds to the location of the river estuary.

[0008] Among them, the spherical distance algorithm uses the great circle distance method to calculate the surface distance between adjacent coordinate points.

[0009] Among them, the specific way of calculating the river slope parameter by the segmented weighted method is: using the distance between adjacent coordinate points as the weight, dividing the product of the elevation difference of each segment and the segment length after cumulative addition by the square of the total length.

[0010] Among them, it also includes: receiving the starting and ending point coordinates input by the user through a browser or a server architecture platform; rendering the vector graph of the target river section in real time and outputting the calculation results of the river length and river slope parameters.

[0011] Beneficial effects 1. The present invention prepares the global DEM dataset, flow direction raster dataset, and cumulative flow raster dataset in advance, and proposes a method for quickly extracting the flow path of any river section based on the flow direction raster and cumulative flow raster data. Only by allowing the user to determine the upstream and downstream starting and ending point coordinates can the water flow path of the target river section be quickly extracted and vectorized for rendering, achieving the second-level extraction of the river length and gradient of any river section globally.

[0012] 2. The present invention introduces the Haversine formula to calculate the spherical distance between adjacent coordinate points of the target river section point by point, effectively reducing the calculation error of the river length. The segmented weighted gradient method is adopted, with the distance between two pixels as the step length for segmentation, and the segmentation method is more refined, resulting in higher accuracy of the gradient calculation result.

[0013] 3. The present invention develops a river channel parameter extraction platform based on the B / S architecture. Users can quickly extract river section parameters and generate corresponding river section vector data by arbitrarily clicking or inputting the starting and ending point positions of the river section through the platform.

[0014] 4. Traditional GIS software needs to perform steps such as depression filling calculation, flow direction analysis, cumulative flow analysis, and river network generation in sequence to extract the water system, which takes a long time. The present invention directly uses the preprocessed dataset, tracks the river flow path through the flow direction raster, and takes the cumulative flow of 0 as the termination condition to ensure that the path is completely tracked to the estuary, significantly simplifying the calculation process and greatly improving the calculation efficiency.

[0015] 5. Based on the geographical coordinates of two points, upstream and downstream, of the same river channel, the present invention quickly extracts the flow path between the upstream and downstream river sections through spatial topological relationships, and can arbitrarily define the position of the target river section, with extremely high flexibility and practicality.

[0016] 6. The method for quickly extracting river channel parameters at any location globally according to the present invention is coded by algorithms and developed into a software platform using the B / S architecture. It can realize arbitrarily clicking or inputting the starting and ending point positions of the river section on the platform, quickly extracting the river section parameters and rendering and generating the corresponding river section vector data, providing an efficient and reliable tool support for hydrological analysis, water resource management, and engineering decision-making, and having broad application value and popularization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flowchart of the technical solution of a method for quickly extracting river channel parameters at any location globally according to the present invention.

[0018] Figure 2 It is a schematic diagram of a certain target river section and the starting and ending point positions of the river section in Wujiang River in an embodiment of the present invention.

[0019] Figure 3 It is a diagram of the water flow law of the flow direction raster in an embodiment of the present invention.

[0020] Figure 4 This is the flow path map from the starting point to the river estuary of the target river section in the embodiment of the present invention.

[0021] Figure 5 This is the flow path map from the ending point to the river estuary of the target river section in the embodiment of the present invention.

[0022] Figure 6 This is the flow path map of the target river section in the embodiment of the present invention.

[0023] Figure 7 This is the schematic diagram of the parameter extraction result of the target river section in the embodiment of the present invention. Detailed implementation manners

[0024] The present invention will be described in detail below with reference to the accompanying drawings and by way of examples.

[0025] The present invention proposes a method for quickly extracting parameters of any river channel in the world. The process is as Figure 1 shown and includes the following steps: Step 1: Prepare and correct the global DEM data to generate a high-precision flow direction and cumulative flow raster dataset; Step 2: Determine any target river section in the world, input the geographical coordinates of the starting and ending points of the river section, and through the accurate mapping between geographical coordinates and pixel coordinates, and in combination with the water flow direction law of the flow direction raster, generate the flow path coordinates from the starting point and the ending point of the target river section to the estuary respectively; Step 3: Based on the flow path coordinates from the starting point and the ending point of the river section in Step 2 to the estuary, and in combination with the spatial topological relationship between the upstream and downstream of the two paths, extract the river path coordinates between the river sections; Step 4: Based on the river path coordinates between the river sections in Step 3, obtain the elevation of the corresponding coordinate points and calculate the distance between adjacent coordinate points, and calculate the parameters of the river section.

[0026] Furthermore, the specific steps included in Step 1 are as follows: (1-1) Prepare the global DEM dataset, perform spatial comparison between the water system information extracted from high-resolution remote sensing images or other data sources and the original DEM data, and perform hydrological registration and correction on the DEM data to obtain the corrected DEM dataset DEM_adj; (1-2) After performing filling and excavation calculations on DEM_adj, use GIS software to generate the global flow direction raster data Dir_raster and the global cumulative flow raster data Accum_raster.

[0027] Furthermore, the specific steps included in Step 2 are as follows: (2-1) Input the longitude and latitude coordinates (Lon_s1, Lat_s1) of the starting point of any target river section globally. Lon_s1 is the longitude coordinate of the starting point, and Lat_s1 is the latitude coordinate of the starting point. Use the geographic information attributes of DEM_adj to convert the longitude and latitude coordinates (Lon_s1, Lat_s1) into pixel coordinates (X_s1, Y_s1); (2-2) Starting from the pixel coordinates (X_s1, Y_s1) of the starting point of the river section, according to the flow law of the flow direction raster, continuously traverse the pixel values of Dir_raster and Accum_raster through iterative calculation. In each iteration, record the flow direction value Dir_values_i and the cumulative flow value Accum_raster_i of the current point (i = 1, 2, 3,...), and store the pixel coordinates obtained at each step in a set. When Accum_raster_i = 0, stop traversing, indicating that the current pixel coordinate position has reached the estuary position of the river. Finally, the set of river path coordinates from the starting point to the estuary of the river section is denoted as XY_s = {(X_s1, Y_s1), (X_s2, Y_s2),..., (X_sn, Y_sn)}, where (X_sn, Y_sn) is the pixel coordinate corresponding to the river estuary; (2-3) Select any position downstream of the target river section in (2-1) as the end point of the river section, and its longitude and latitude coordinates are (Lon_e1, Lat_e1). Repeat (2-1) and (2-2), and finally obtain the set of river path coordinates from the end point to the estuary of the river section as XY_e = {(X_e1, Y_e1), (X_e2, Y_e2),..., (X_en, Y_en)}, where (X_en, Y_en) is the pixel coordinate corresponding to the position where the river estuary is located.

[0028] Further, step 3 includes the following specific steps: (3-1) Re-convert the pixel coordinate sets XY_s and XY_e obtained in step (2-2) and step (2-3) into longitude and latitude coordinates. The set of longitude and latitude coordinates obtained by converting XY_s is LonLat_s = {(Lon_s1, Lat_s1), (Lon_s2, Lat_s2),..., (Lon_sn, Lat_sn)}, and the set of longitude and latitude coordinates obtained by XY_e is LonLat_e = {(Lon_e1, Lat_e1), (Lon_e2, Lat_e2),..., (Lon_en, Lat_en)}; (3-2) The coordinates (Lon_s1, Lat_s1) and (Lon_e1, Lat_e1) are located upstream and downstream of the target river section, respectively. Therefore, LonLat_s contains LonLat_e. Based on LonLat_s, the elements in LonLat_e other than (Lon_e1, Lat_e1) are deducted to obtain the longitude and latitude coordinate set of the river section including the starting and ending points, which is recorded as LonLat_a = {(Lon_1, Lat_1), (Lon_2, Lat_2), … (Lon_a, Lat_a)}, where a is the number of river section coordinate points. The pixel coordinate set corresponding to LonLat_a is XY_a = {(X_1, Y_1), (X_2, Y_2), …, (X_a, Y_a)} Furthermore, the step 4 includes the following specific steps: (4-1) Use the Haversine formula to sequentially calculate the distances between two adjacent coordinate points in the target river section, denoted as {l1, l2, l3, …, la-1}. Sum the distances between the two adjacent points to obtain the river section length, denoted as L. Use the river section pixel coordinates XY_a to obtain the elevation values of the corresponding points from DEM_adj, denoted as {h0, h1, h2, …, ha}.

[0029] The Haversine formula is as follows:

[0030] : spherical distance between two coordinate points (kilometers); : The radius of the Earth, usually taken as 6371 km (average radius); , : latitude of two coordinate points; , : longitude of two coordinate points; : the difference in latitude between two points; : The difference in longitude between two points.

[0031] (4-2) According to the formula for calculating the weighted gradient of the river section, the gradient J of the river section is calculated. The formula for calculating the weighted gradient of the river section is as follows:

[0032] : is the weighted gradient of the river section; : is the elevation corresponding to each coordinate from upstream to downstream of the target river section (m); : is the elevation (m) corresponding to each coordinate from the upstream to the downstream of the target river reach; : is the total length of the river reach (m).

[0033] Experimental verification: Select a certain river reach in Wujiang River, Guizhou Province as the experimental verification object of the method of the present invention. The target river reach, the coordinates of the starting point at the upstream of the target river reach and the coordinates of the ending point at the downstream of the target river reach are as Figure 2 shown. The detailed steps are as follows: Step 21: Prepare and correct to generate a global DEM dataset, a global flow direction raster data Dir_raster and a global accumulated flow raster data Accum_raster; Step 22: Select any target river reach globally, obtain the longitude and latitude coordinates (Lon_s1, Lat_s1) of the starting point at the upstream of the target river reach. The position of the starting point is as Figure 2 shown. Use the geographic information attributes of DEM_adj to convert the longitude and latitude coordinates (Lon_s1, Lat_s1) into pixel coordinates (X_s1, Y_s1); Step 23: Starting from the pixel coordinates (X_s1, Y_s1) of the starting point of the target river reach, according to the flow law of the flow direction raster (such as Figure 3 ), continuously traverse the pixel values of Dir_raster and Accum_raster through iterative calculation. In each iteration, record the flow direction value Dir_values_i and the accumulated flow value Accum_raster_i of the current point (i = 1, 2, 3,...), and store the pixel coordinates obtained in each step in a set. When Accum_raster_i = 0, stop traversing, indicating that the position where the current pixel coordinates are located has reached the estuary position of the river. Finally, obtain the set of river path coordinates from the starting point to the estuary of the target river reach, denoted as XY_s = {(X_s1, Y_s1), (X_s2, Y_s2),..., (X_sn, Y_sn)}, where (X_sn, Y_sn) is the pixel coordinates corresponding to the river estuary. Convert XY_s back into longitude and latitude coordinates LonLat_s = {(Lon_s1, Lat_s1), (Lon_s2, Lat_s2),..., (Lon_sn, Lat_sn)}, render LonLat_s into vector data and display it on the map, as Figure 4 shown. Figure 4 This is the flow path map from the starting point to the river estuary of the target river reach in the embodiment of the present invention.

[0034] Step 24: Select any position downstream of the river channel in the set of river path coordinates from the starting point to the estuary of the target river reach as the ending point of the target river reach. The position is as Figure 2As shown, its longitude and latitude coordinates are (Lon_e1, Lat_e1). Repeat the process of step 23. Finally, the set of river path coordinates from the end point of the target river section to the river mouth is XY_e = {(X_e1, Y_e1), (X_e2, Y_e2), …, (X_en, Y_en)}, where (X_en, Y_en) is the pixel coordinate corresponding to the location of the river mouth. Convert XY_e back to longitude and latitude coordinates LonLat_e = {(Lon_e1, Lat_e1), (Lon_e2, Lat_e2), … (Lon_en, Lat_en)}. Render LonLat_e as vector data and display it on the map, as Figure 5 shown. Figure 5 This is the flow path map of the target river section from the end point to the river mouth in the embodiment of the present invention.

[0035] Step 25: The coordinates (Lon_s1, Lat_s1) and (Lon_e1, Lat_e1) are located at the upstream and downstream positions of the river channel respectively. Therefore, LonLat_s contains LonLat_e. Deduct the elements in LonLat_e except (Lon_e1, Lat_e1) from LonLat_s to obtain the set of longitude and latitude coordinates of the target river section including the starting and ending points, denoted as LonLat_a = {(Lon_1, Lat_1), (Lon_2, Lat_2), … (Lon_a, Lat_a)}, where a is the number of river section coordinate points. The set of pixel coordinates corresponding to LonLat_a is XY_a = {(X_1, Y_1), (X_2, Y_2), …, (X_a, Y_a)}. Render the longitude and latitude coordinates LonLat_a of the target river section as vector data and display it on the map, as Figure 6 shown. Figure 6 This is the river flow path map of the target river section in the embodiment of the present invention.

[0036] Step 26: Use the Haversine formula to calculate the distance between adjacent coordinate points in turn, denoted as {l1, l2, l3, … la-1}. Sum up the coordinate distances between adjacent points to obtain the river section length denoted as L. Use the pixel coordinates XY_a of the river section to obtain the elevation values of the corresponding points from DEM_adj, denoted as {h0, h1, h2, … ha}.

[0037] The Haversine formula is as follows:

[0038] : The spherical distance (in kilometers) between two coordinate points; : The radius of the earth, usually taken as 6371 kilometers (average radius); , : Latitude of two coordinate points; , : Longitude of two coordinate points; : Difference in latitude between two points; : Difference in longitude between two points.

[0039] Step 27: Calculate the slope J of the river reach according to the river reach segmented weighted slope formula. The river reach weighted slope formula is as follows:

[0040] : Weighted slope of the river reach; : Elevation (m) corresponding to each coordinate from upstream to downstream of the target river reach; [[ID=ID=28]] : Elevation (m) corresponding to each coordinate from upstream to downstream of the target river reach; : Total length (m) of the river reach.

[0041] The calculation results of the river length and slope of the target river reach calculated by the present invention are as Figure 7 shown. Figure 7 It is a schematic diagram of the target river reach parameter extraction result in the embodiment of the present invention.

[0042] The method of the present invention can be implemented by a global river channel parameter rapid extraction system, and the system includes: A preprocessing module for storing global DEM_adj, Dir_raster, and Accum_raster data sets; A path tracing module for performing the flow path extraction operation of the method of the present invention; A parameter calculation module for performing the calculation of the river length and slope of the method of the present invention; A visualization module for rendering the river reach vector data and displaying the parameter results.

[0043] Among them, the path tracing module is configured to use the cumulative flow value = 0 as the path termination determination condition; The parameter calculation module integrates the Haversine formula and the segmented weighted slope algorithm.

[0044] The accompanying drawings illustrate the preferred embodiments of the present invention, not the only embodiments. It should be noted that, according to the flow direction data, the flow path of the river is traced, and the flow direction grid may include, but is not limited to, mainstream algorithms such as D8, MFD, etc. In the method for generating the river flow path between river reaches of the present invention, it is not limited to first obtaining the flow path of the upstream starting point, and the flow path of the downstream point of the river reach may also be obtained first, and there is no distinction in the order.

[0045] The terms such as variable names and coordinate names involved in the present invention are only defined for the convenience of describing the technical solution and are not the only naming methods. The present invention traverses the flow direction grid and the cumulative flow grid, and stores the obtained pixel coordinates in a set. Storing them in a set is just a way for the present invention to facilitate calculation, and other data storage methods may also be used.

[0046] Unless otherwise specified, all technical and scientific terms used herein have the meanings commonly understood by those skilled in the art; the terms in the specification are only used to describe specific embodiments and do not constitute a limitation on the protection scope of the present invention.

[0047] In summary, the above are only the preferred embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for quickly extracting parameters of any river channel globally, characterized in that It includes the following steps: Preprocessing step: Correcting the global digital elevation model data and generating a global flow direction raster dataset and an accumulated flow raster dataset; Path tracing step: Inputting the longitude and latitude coordinates of the starting point of the global target river reach, and converting the longitude and latitude coordinates of the starting point into starting point pixel coordinates by using the geographic information attributes of the global flow direction raster dataset and the accumulated flow raster dataset; Starting from the starting point pixel coordinates, in accordance with the flow law of the flow direction raster data, traversing the pixel values of the flow direction raster and the accumulated flow raster through iterative calculation, recording the flow direction value and the accumulated flow value of the current point in each iteration, and storing the pixel coordinates obtained in each step; Stop traversing when the accumulated flow value is equal to zero to obtain a set of river path pixel coordinates from the starting point of the river reach to the estuary; Inputting the longitude and latitude coordinates of the end point downstream of the target river reach, and repeating the above conversion and iterative tracing process to obtain a set of river path pixel coordinates from the end point of this river reach to the estuary; River reach extraction step: Respectively converting the set of pixel coordinates from the starting point to the estuary and the set of pixel coordinates from the end point to the estuary into corresponding sets of longitude and latitude coordinates; Based on the relationship that the longitude and latitude coordinates of the starting point and the end point are located upstream and downstream of the target river reach, on the basis of the set of longitude and latitude coordinates from the starting point to the estuary, deducting all elements except the end point coordinates in the set of longitude and latitude coordinates from the end point to the estuary to obtain a set of longitude and latitude coordinates of the target river reach including the starting point and the end point; The set of pixel coordinates corresponding to the set of longitude and latitude coordinates of the target river reach is the set of target river reach pixel coordinates; Parameter calculation step: Extracting a high-order sequence from the digital elevation model data based on the set of target river reach pixel coordinates, obtaining the river length parameter by cumulatively adding the distances between adjacent points point by point through the spherical distance algorithm, and calculating the river slope parameter by using the piecewise weighting method.

2. The method according to claim 1, characterized in that: The preprocessing step includes correcting the original digital elevation model by using high-resolution remote sensing image water system data to generate corrected elevation data, and performing depression filling calculation on this data to generate a flow direction raster dataset and an accumulated flow raster dataset.

3. The method according to claim 1 or 2, characterized in that: In the path tracing step, the determination condition for the accumulated flow value to be 0 corresponds to the location of the river estuary.

4. The method according to claim 3, wherein: The spherical distance algorithm uses the great circle distance method to calculate the surface distance between adjacent coordinate points.

5. The method according to claim 1 or 2, characterized in that: The specific way of calculating the river slope parameter by the piecewise weighting method is: Using the distance between adjacent coordinate points as the weight, dividing the sum of the products of the elevation differences of each segment and the segment lengths by the square of the total length after accumulation.

6. The method according to claim 1 or 2, characterized in that, It also includes: Receiving the starting and ending point coordinates input by the user through a browser or a server architecture platform; Real-time rendering of the vector graph of the target river reach and outputting the calculation results of the river length and river slope parameters.

Images