CN104537717A - Acquisition method for watercourse underwater terrain thematic map - Google Patents

Abstract

The invention discloses an acquisition method for a watercourse underwater terrain thematic map. The method comprises the following steps that first, a digital elevation model is created according to TIN data generated by elevation points and contour line data; second, optimizing process is carried out on the digital elevation model obtained in the first step; third, an illumination model is created, and the illumination model is utilized to carry out illumination model process on the digital elevation model optimized in the second step; fourth, model superposition and rendering are carried out, and then displaying is carried out. According to the acquisition method for the watercourse underwater terrain thematic map, the more vivid and intuitive watercourse thematic map with third dimension can be acquired; the variation trend of the watercourse terrain can be intuitively reflected, the availability in actual production is strong, and the appreciation is provided; meanwhile, the drawing efficiency is high, the production cost is low, and batch drawing can be accomplished by a procedure according to thematic map parameters.

Description

A method for acquiring thematic map of river underwater topography

technical field

The invention belongs to the technical field of river channel mapping, and the invention relates to a method for acquiring a river channel underwater terrain thematic map.

technical background

A thematic map, also known as a special map, is a map that focuses on one or several natural elements or social and economic phenomena. The content of the thematic map consists of two parts: ①Thematic content. Natural or socio-economic phenomena and their associated characteristics highlighted on the map. ②Geographic basis. Common map content used to indicate the spatial location and geographical background of thematic elements mainly includes graticules, water systems, boundaries, and residential areas.

The river topography thematic map is a special map that reflects river topography information, highlighting the river topography information. Thematic river topographic maps play an important role in the development and improvement of rivers, flood control, water supply, shipping and other important issues related to the sustainable development of social economy and river ecological balance. The topographic map of the river course is a necessary data source for the overall planning of the river course, river course management, and embankment engineering construction.

The research on the evolution and improvement of the river bed is inseparable from the visualization of the river topography. At present, the river topographic map is used to describe the river channel information. The content and form are single, the expression is not intuitive enough, and the professional requirements are strong. It is very necessary to make a topographic map with good visualization effect in order to accurately display the change of river bed topography and the change trend of river topography. However, in the prior art, this aspect is still very lacking.

Contents of the invention

Purpose of the invention: The purpose of the present invention is to address the deficiencies in the prior art, and propose a method for acquiring a thematic map of river channel underwater topography with good mapping effect, more accurate mapping and strong usability.

Technical solution: The present invention provides a method for acquiring a thematic map of underwater topography of a river course, comprising the following steps:

Step 1: Obtain the elevation points and contour line data of the underwater terrain through measurement, select the elevation value in the attribute as the height source, use the contour line as the hard partition line, and the elevation points as discrete multi-points to generate an irregular triangulation ( triangulated irregular network, hereinafter referred to as TIN), to create a digital elevation model of the river;

Step 2: Optimizing the digital elevation model obtained in step 1;

Step 3: Simulate the effect of sunlight irradiation, set the elevation angle and azimuth angle of the light source, and establish an illumination model on the basis of the digital elevation model optimized in step 2;

Step 4: Superposition, rendering and display of digital elevation model and illumination model.

Further, the optimization processing method in the step 2 includes the following steps:

Step 201: using the digital elevation model to create dense contour lines;

Step 202: optimize the contour line according to the specified threshold, and delete the contour line whose length is less than the threshold value, wherein the determination of the threshold value is related to the quality of the data, and the threshold value is determined in a ratio of one thousandth, that is, the data below the threshold value The amount is one-thousandth of the overall data;

Step 203: using the contour line optimized in step 202, repeat step 1 to generate a digital elevation model;

Step 204: smoothing the digital elevation model generated in step 203;

Step 205: Set a critical value, the critical value is the maximum allowable difference between the depth of the sink point and the pouring point, and fill all the sinking points that are smaller than the critical value and lower than its lowest adjacent pixel to its pouring point The height of , so as to remove the fine terrain in the digital elevation model, where the sink point refers to the pixel with undefined watershed direction; the surrounding pixels are higher than it, and the pour point is the boundary with the lowest elevation of the confluence area relative to the sink point pixel.

Step 206: Optimizing the steep terrain in the digital elevation model.

Further, the illumination model processing is based on the illumination and shadow theory of the mountain, combined with the angle and shadow of the illumination source, to create a method for creating river topography shading and generating a river topography shadow map.

Further, the step 4 mainly includes the following steps:

Step 401: setting rendering parameters in the digital elevation model;

Step 402: setting the rendering parameters of the river terrain shadow map;

Step 403: superimpose and display the rendering parameters processed in steps 401 and 402.

Beneficial effects: Compared with the prior art, the present invention can obtain a more vivid, more intuitive and three-dimensional river channel thematic map; at the same time, it can intuitively reflect the change trend of the river channel topography, and has strong usability in actual production, and has the advantages of Appreciation; moreover, the present invention is different from the popular three-dimensional simulation modeling, which requires multiple tasks such as modeling, transformation, and complex rendering. The present invention establishes a GIS-based model, which has high drawing efficiency and low production cost. Parameters are programmed to complete batch drawing.

Description of drawings

Fig. 1: schematic flow sheet of the present invention;

Figure 2: Raw data graph;

Figure 3: The result of digital elevation model optimization;

Figure 4: The results of lighting model establishment;

Figure 5: Data overlay visualization result map;

Figure 6: Final result map.

Detailed ways

The following part of the underwater terrain data of Baguazhou in the Nanjing section of the Yangtze River is selected, and the data is obtained from the underwater terrain survey at the Nanjing River. The implementation of the present invention will be further described in conjunction with the accompanying drawings and examples, but the implementation and inclusion of the present invention are not limited thereto.

As shown in Figure 1, the river channel underwater terrain thematic map acquisition method provided by the present invention comprises the following steps:

Step 1: Generate a digital elevation model; it mainly includes the following steps:

Step 101, as shown in Figure 2, obtain the elevation points and contour line data obtained from the underwater topographic survey from the Nanjing river, select the elevation value in the attribute as the height source, use the contour line as the hard cut-off line, and the elevation point is Discrete multiple points, generate TIN and convert it into raster data format, retain the elevation value of the data, that is, create a digital elevation model of the LE river. Among them, use the generate TIN tool in the channel mapping tool set to generate TIN data from the elevation point and contour line data. The river mapping tool set is a special tool set for river mapping developed for the completion of this patented river mapping. It can be imported and used in ArcMap software. The tool set is written by the python script language based on ArcGIS10.2, including batch generation of TIN, TIN conversion Raster, extract contour lines and other functions.

Step 102, using the TIN-to-raster tool in the channel mapping tool set, adopting the natural neighbor method for interpolation, setting the resampling pixel size of the output raster to 1, and converting the TIN irregular triangulation network into a digital elevation model.

Step 2: Optimizing the digital elevation model; this step includes the following sub-steps:

Step 201, using the elevation model to extract contours; using the tool for extracting contours in the channel mapping tool set, first vectorize the raster data, and then perform fitting to extract contours, where the distance between contours should be smaller than the original contour Spacing of high lines.

Step 202, optimize the contour line according to the specified threshold value; use the contour line optimization tool of the river mapping tool set, set the threshold value according to the graphic length attribute of the contour line, and remove the fine contour lines whose length is less than the threshold value, wherein The determination of the threshold is related to the quality of the data, and the threshold size is determined at a ratio of one-thousandth, that is, the amount of data below the threshold is one-thousandth of the overall data.

Step 203, using the contour optimized in step 202 to generate a digital elevation model and combining the contour optimized in step 102 to generate an optimized digital elevation model;

Step 204, smoothing the digital elevation model; smoothing the river topography by using the smoothing tools of the river mapping toolset. The smoothing model formula is:

Con(dem>=0, Int(dem)+0.5, Int(dem)-0.5)

In the formula, dem is the digital elevation model data that needs to be smoothed.

Step 205, removing abnormal terrain in the digital elevation model; using the abnormal terrain processing tool in the river mapping tool set, set the critical value, that is, the maximum allowable difference between the depth of the depression point and the pour point, which will be less than the critical value and lower than All the depression points of its lowest adjacent pixel are filled to the height of its pour point, thereby removing the fine terrain in the digital elevation model and realizing further smoothing of the digital elevation model. Among them, the sink point refers to the pixel with no defined watershed direction; the surrounding pixels are higher than it, and the pour point is the boundary cell with the lowest elevation of the confluence area relative to the sink point;

Step 206, optimizing the steep terrain in the digital elevation model. The topography changes rapidly on both sides of the river, forming steep slopes. In the digital elevation model, relatively dense steep slope lines will be formed. If the steep slope optimization process does not affect the topographic trend of the river, it will have a more intuitive visualization effect. Use the Steep Slope Optimization tool in the Channel Mapping toolset to optimize steep slope areas in your digital model.

As shown in Figure 3. In the digital elevation model optimization result map, the river topography is represented by shades of colors, dark colors represent lower-altitude river sections, and light colors represent higher-altitude river sections. At the same time, the river channel elevation is divided into 18 levels for display according to the altitude difference.

Step 3: Establish the lighting model; according to the lighting theory model, the terrain shadow map will be generated to make the terrain map have an intuitive three-dimensional effect. Use the river channel shadow tool in the river channel mapping tool set to set the azimuth angle and elevation angle parameters. According to the visual principle of the human eye to produce a two-dimensional map with a three-dimensional sense, the azimuth angle is set to 315°, and the altitude angle is set to 45° for the best effect. Lighting model building result graph. As shown in Figure 4, the sunken effect represents the lower-altitude river reach, and the raised effect represents the higher-altitude river reach. The contour line on the sunny side is the bright line, and the contour line on the shady side is the dark line.

Step 4: Model overlay, rendering and display; mainly includes the following steps:

Step 401: digital elevation model rendering parameter setting; open the layer properties dialog box of the data in ArcMap software to perform unique value rendering on the data processed in step 4, and select the gradient color from light gray to dark gray for the rendering color band.

Step 402: Setting the rendering parameters of the river terrain shadow map; the shadow map rendering is opened in the ArcMap software to generate the shadow map, and the shadow map is stretched and rendered, and the color band is selected from light gray to dark gray.

Step 403: Superimpose and display the data processed in steps 401 and 402. Open the layer properties dialog box of the digital elevation model in the ArcMap software, set its transparency to 30% in the display toolbar, and overlay it on the shadow map, as shown in Figure 5. In the data overlay visualization result graph, the depth of the river channel is displayed by both the color depth and the surface unevenness. A darker, sunken effect indicates a lower-elevation reach, and a lighter, raised effect indicates a higher-elevation reach. You can also do map finishing; such as inserting a scale bar, compass, legend, etc. in the map. The final result map is shown in Figure 6.

Claims (4)

1. A method for obtaining a thematic map of underwater topography of a river course, is characterized in that, comprises the following steps: Step 1: Obtain the elevation point and contour line data of the underwater terrain through measurement, select the elevation value in the attribute as the height source, use the contour line as the hard partition line, and the elevation points as discrete multi-points to generate an irregular triangulation network. Create a digital elevation model of the river; Step 2: Optimizing the digital elevation model obtained in step 1; Step 3: Simulate the effect of sunlight irradiation, set the elevation angle and azimuth angle of the light source, and establish an illumination model on the basis of the digital elevation model optimized in step 2; Step 4: Superposition, rendering and display of digital elevation model and illumination model. 2. the river course underwater topography thematic map acquisition method according to claim 1, is characterized in that: in described step 2, optimization processing method comprises the following steps: Step 201: using the digital elevation model to create dense contour lines; Step 202: optimize the contour according to the specified threshold, and delete the contour whose length is smaller than the threshold; Step 203: using the contour line optimized in step 202, repeat step 1 to generate a digital elevation model; Step 204: smoothing the digital elevation model generated in step 203; Step 205: Set a critical value, the critical value is the maximum allowable difference between the depth of the sink point and the pouring point, and fill all the sinking points that are smaller than the critical value and lower than its lowest adjacent pixel to its pouring point The height of , so as to remove the fine terrain in the digital elevation model, where the sink point refers to the pixel with undefined watershed direction; the surrounding pixels are higher than it, and the pour point is the boundary with the lowest elevation of the confluence area relative to the sink point pixel; Step 206: Optimizing the steep terrain in the digital elevation model. 3. The method for obtaining the thematic map of river underwater topography according to claim 1, characterized in that: the illumination model is based on the light and shadow theory of the mountain, combined with the angle and shadow of the illumination source, creating the shading of the river channel landform to generate the channel Processing model for terrain shadow maps. 4. the river course underwater terrain thematic map acquisition method according to claim 1, is characterized in that: described step 4 mainly comprises the following steps: Step 401: setting rendering parameters in the digital elevation model; Step 402: setting the rendering parameters of the river terrain shadow map; Step 403: superimpose and display the rendering parameters processed in steps 401 and 402.