A DEM data filtering method, device, system and storage medium

Abstract

The present invention discloses a DEM data filtering method and device, system, and storage medium, comprising: step S1, obtaining terrain feature lines according to DEM data; step S2, obtaining texture profile lines according to the terrain feature lines; step S3, performing Fourier filtering on the texture profile lines to obtain simplified texture profile lines; step S4, embedding the simplified texture profile lines into the DEM data. By adopting the technical solution of the present invention, large-scale landform data can be derived from small-scale DEM data to accurately and effectively reflect the multi-scale characteristics of the landform.

Description

Technical Field

[0001] The present invention belongs to the technical field of image processing, and in particular relates to a DEM data filtering method and device, a system, and a storage medium. Background Art

[0002] Landforms are the foundation for human survival and all practical activities. The global surface elevation controls the redistribution of water and heat on the earth's surface, and regional surface undulations affect local hydrology, soil, and the activities of plants, animals, and humans. Digital elevation models (DEMs) are used to describe the elevation information and undulations of the earth's surface. In the process of scientific research and production, it is necessary to obtain DEM data of different scales to meet data requirements at different levels. At present, it is impossible to use small-scale DEM data to derive large-scale landform data to accurately and effectively reflect the multi-scale characteristics of landforms. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a DEM data filtering method and device, system, and storage medium, which can use small-scale DEM data to derive large-scale landform data to accurately and effectively reflect the multi-scale characteristics of the landform.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A DEM data filtering method, characterized by comprising:

[0006] Step S1, obtaining terrain characteristic lines according to DEM data;

[0007] Step S2, obtaining a texture profile line according to the terrain feature line;

[0008] Step S3, performing Fourier filtering on the texture profile line to obtain a simplified texture profile line;

[0009] Step S4: mosaicking the simplified texture profile lines into the DEM data.

[0010] Preferably, the terrain feature lines include: ridge lines and valley lines.

[0011] Preferably, step S2 comprises:

[0012] Delineate texture units according to the range of topographic feature lines;

[0013] Extract the texture profile along the feature line direction within the texture unit.

[0014] Preferably, in step S3, the texture profile line is subjected to elevation low-pass filtering based on the Fourier spectrum to obtain a simplified texture profile line.

[0015] The present invention also provides a DEM data filtering device, comprising:

[0016] The first extraction module is used to obtain terrain characteristic lines according to DEM data;

[0017] The second extraction module is used to obtain a texture profile line according to the terrain feature line;

[0018] A filtering module, used for performing Fourier filtering on the texture profile to obtain a simplified texture profile;

[0019] The mosaic module is used to mosaic the simplified texture profile lines into the DEM data.

[0020] Preferably, the terrain feature lines include: ridge lines and valley lines.

[0021] Preferably, the second extraction module comprises:

[0022] Delineating units, used to delineate texture units according to the range of action of terrain feature lines;

[0023] The extraction unit is used to extract the texture section line along the characteristic line direction in the texture unit.

[0024] Preferably, the filtering module is used to perform elevation low-pass filtering on the texture profile line based on the Fourier spectrum to obtain a simplified texture profile line.

[0025] The present invention also provides a DEM data filtering system, comprising: a memory and a processor, wherein the memory stores a computer program to be run by the processor, and the computer program executes the DEM data filtering method when being run by the processor.

[0026] The present invention also provides a storage medium, on which a computer program is stored, and the computer program executes the DEM data filtering method when running.

[0027] The present invention extracts terrain feature lines from DEM data, delineates texture units according to the range of action of the terrain feature lines; extracts profile lines along the feature line direction in the unit at certain intervals, performs elevation low-pass filtering on each profile line based on the Fourier spectrum; finally, replaces the DEM elevation value of the unit with the elevation value of each filtered profile to achieve the purpose of DEM fine filtering. The present invention maintains and strengthens the trend of the texture unit landform, and controls the elevation error by using the cutoff frequency to achieve DEM expression at different levels of detail, achieving the comprehensive goal of "retaining the main landform morphological features and discarding the secondary landform morphological features". BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0029] Figure 1 This is a flow chart of a DEM data filtering method according to an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the process of delineating texture units and generating elevation profiles for specific terrain feature lines; (a) delineating texture units; (b) generating parallel lines of terrain feature lines; (c) collecting equally spaced elevation points; (d) generating elevation profiles;

[0031] Figure 3 This is a schematic diagram of the DEM profile line;

[0032] Figure 4 Schematic diagram of Fourier filtering of cross-section data, where (a) mirror processing of cross-section data and (b) cross-section data after filtering;

[0033] Figure 5 It is a schematic diagram of the average elevation error;

[0034] Figure 6 Comparison diagram of the texture unit profile before and after integration, where (a) is the profile before integration, and (b) is the profile before integration. DETAILED DESCRIPTION

[0035] 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.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Embodiment 1:

[0038] like Figure 1 As shown, the present invention provides a DEM data filtering method, comprising:

[0039] Step S1, obtaining terrain feature lines according to DEM data, wherein the terrain feature lines include: ridge lines and valley lines;

[0040] Step S2, obtaining a texture profile line according to the terrain feature line;

[0041] Step S3, performing Fourier filtering on the texture profile line to obtain a simplified texture profile line;

[0042] Step S4: mosaic the simplified texture lines into the DEM data.

[0043] As an implementation of the embodiment of the present invention, step S2 includes:

[0044] Delineate texture units according to the range of topographic feature lines;

[0045] Extract the texture profile along the feature line direction within the texture unit.

[0046] Furthermore, the terrain feature line represents the surface undulation within a certain range around it, and the buffer area at a certain distance to the side of each terrain feature line is its texture unit. The width of the texture unit is affected by factors such as the level of the terrain feature line, the distance between adjacent parallel feature lines, and the fragmentation of the terrain. The higher the level, the greater the adjacent distance, and the smaller the fragmentation, the larger the width of the texture unit, and vice versa. In practical applications, the distance between two adjacent parallel terrain feature lines can be taken as the width of the texture unit. Figure 2 (a) is the texture unit corresponding to each valley line in the experimental area. In each texture unit, multiple parallel lines with a spacing of 1 / 2 grid size of DEM are generated along both sides of the feature line. The elevation change of each parallel line is similar to that of the terrain feature line. Figure 2 (b) shows that a certain terrain feature line is 9 parallel lines with an interval of 30m. On each parallel line, sampling is performed at an interval of 1 / 2 the grid size of the DEM. Figure 2 (c) in the figure is to collect points at intervals of 30 meters on each parallel line. The elevation of each point is taken from the elevation of the nearest DEM grid point, and finally the following is formed: Figure 2 The 9 high-level section lines shown in (d) in FIG.

[0047] As an implementation of the embodiment of the present invention, in step S3, the texture profile line is subjected to elevation low-pass filtering based on the Fourier spectrum to obtain a simplified texture profile line.

[0048] Furthermore, the texture profile line is a string of coordinate points connected by a series of elevation points. Figure 3 The point sequence P0, P1, ..., P N The DEM profile line is constructed with the horizontal coordinate being the horizontal distance from the point to the starting point and the vertical coordinate being the elevation value. The elevation of any point P on the texture profile line can be expressed as a piecewise function H(l) of the horizontal distance l from the point to the starting point P0, that is.

[0049]

[0050] Among them, H i , H i+1 Point P i , P i+1 The elevation value of i , L i+1 From the starting point P0 to the point P i , P i+1 Horizontal distance; L i ≤l≤L i+1 ; 0≤i≤N-1; N is the number of sampling points in the section, which is a positive integer.

[0051] Texture profile lines represent the topographic trend in a certain direction. Profile lines of the same texture unit generally have similar shape characteristics. DEM data of different scales correspond to profile line expressions of different levels of detail. The two constitute an isomorphic relationship, that is, DEM simplification can be achieved by simplifying texture profile lines. The embodiment of the present invention uses Fourier filtering to achieve simplification of texture profile lines. The Fourier low-pass filtering of line elements can well maintain the overall shape of the elements and filter the detail information, and can also make the line elements continuous and smooth.

[0052] In order to avoid the "Gibbs" effect in Fourier transform, the texture profile line is extended evenly by using a mirror image method, such as Figure 4 In (a), the extended profile function H(l) becomes an even function E(l) with a period of 2N, that is.

[0053]

[0054] Among them, E(l) is an even function, and it is easy to know that B n =0. The larger the n, the higher the frequency. By controlling the cutoff frequency To obtain the section lines at different expression scales. Figure 4 In (b), it can be seen that the simplified texture profile line maintains the basic undulations of the original profile line, but filters out the detail information. The Fourier cutoff frequency depends on the scale to be expressed, and the scale corresponds to the fine program of the DEM. The embodiment of the present invention calculates the cutoff frequency through the average elevation fitting error of the texture profile line. Figure 5 As shown in the figure, the average value of the difference between the elevation point on the original profile line and the elevation point at the same position on the reconstructed curve is used as a measure of the fitting error between the reconstructed curve and the original profile line, that is:

[0055]

[0056] Among them, ΔH is the fitting error between the original DEM profile and the reconstructed curve, H iPoint P on the original section line i The elevation value, H' i is the elevation of the corresponding point in the reconstructed curve. The number of Fourier expansion terms of different profile lines is determined by setting the average elevation fitting error.

[0057] All texture units in the DEM data are sorted from low to high according to the level of their characteristic lines, and the profile lines of the texture units are processed by Fourier low-pass filtering using the method in this section to obtain simplified profile lines. Figure 6 (a) and (b) in the figure show the comparison of texture unit before and after simplification.

[0058] As an implementation method of an embodiment of the present invention, in step S4, each texture profile line in the texture unit generates a rough expression of the topography of a specific section after Fourier filtering, and all the elevation point data in each texture profile line forms a simplified topographic expression of the texture unit. The nearest neighbor elevation assignment method is adopted to assign the elevation of each DEM point in the texture unit to the elevation of the nearest grid point in the texture unit, thereby achieving the purpose of mosaicking the integrated texture unit into the original DEM. First, the DEM data is mean filtered according to the 7×7 template, and then all the integrated texture units are mosaicked into the original DEM data one by one according to the level of the terrain feature line from low to high, and finally a simplified DEM is obtained. In the mosaicking process, a certain area may be mosaicked multiple times. Since these areas belong to texture units of different levels, the final result is the elevation corresponding to the texture unit of the highest level.

[0059] The embodiment of the present invention takes into account the terrain fluctuations represented by the terrain feature lines, divides the DEM into several texture units, and converts the texture unit geomorphic filtering into the filtering of the profile line according to the linear step characteristics of the texture unit. Finally, the comprehensive results of the texture unit are embedded into the original DEM data to complete the DEM filtering. This method integrates geographical knowledge into digital image processing, fully considers the local characteristics of the terrain fluctuations, and uses the selection of the cutoff frequency in the Fourier filter to achieve the expression of different levels of detail of the DEM data. The comprehensive result achieves the comprehensive geomorphic effect of "maintaining the main terrain feature lines and removing the secondary feature lines". The embodiment of the present invention can not only more accurately express the terrain skeleton line and the main geomorphic features, but also naturally suppress the small ground fluctuations reflected by the secondary feature lines, so as to achieve the purpose of "discarding the secondary and retaining the main", and achieve a better comprehensive geomorphic effect.

[0060] Embodiment 2:

[0061] The embodiment of the present invention further provides a DEM data filtering device, comprising:

[0062] The first extraction module is used to obtain terrain characteristic lines according to DEM data;

[0063] The second extraction module is used to obtain a texture profile line according to the terrain feature line;

[0064] A filtering module, used for performing Fourier filtering on the texture profile to obtain a simplified texture profile;

[0065] The mosaic module is used to mosaic the simplified texture profile lines into the DEM data.

[0066] As an implementation manner of the embodiment of the present invention, the terrain characteristic lines include: ridge lines and valley lines.

[0067] As an implementation of the embodiment of the present invention, the second extraction module includes:

[0068] Delineating units, used to delineate texture units according to the range of action of terrain feature lines;

[0069] The extraction unit is used to extract the texture section line along the characteristic line direction in the texture unit.

[0070] As an implementation method of an embodiment of the present invention, the filtering module is used to perform elevation low-pass filtering on the texture profile line based on the Fourier spectrum to obtain a simplified texture profile line.

[0071] Embodiment 3:

[0072] The present invention also provides a DEM data filtering system, comprising: a memory and a processor, wherein the memory stores a computer program to be run by the processor, and the computer program executes the DEM data filtering method when being run by the processor.

[0073] Embodiment 4:

[0074] The present invention also provides a storage medium, on which a computer program is stored, and the computer program executes the DEM data filtering method when running.

[0075] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A DEM data filtering method, characterized in that: include: Step S1, obtaining terrain characteristic lines according to DEM data; Topographic feature lines include: ridge lines and valley lines; Step S2, obtaining a texture profile line according to the terrain feature line; Step S3, performing Fourier filtering on the texture profile line to obtain a simplified texture profile line; Step S4, embedding the simplified texture profile into the DEM data; Step S2 includes: Delineate texture units according to the range of topographic feature lines; Extracting texture profile lines along the feature line direction in the texture unit; In step S3, the texture profile line is subjected to elevation low-pass filtering based on the Fourier spectrum to obtain a simplified texture profile line.

2. A DEM data filtering device, characterized in that: include: The first extraction module is used to obtain terrain characteristic lines according to DEM data; Topographic feature lines include: ridge lines and valley lines; The second extraction module is used to obtain a texture profile line according to the terrain feature line; A filtering module, used for performing Fourier filtering on the texture profile to obtain a simplified texture profile; Mosaic module, used to mosaic simplified texture profiles into DEM data; The second extraction module includes: Delineating units, used to delineate texture units according to the range of action of terrain feature lines; An extraction unit, used for extracting a texture section line along a characteristic line direction in a texture unit; The filtering module is used to perform elevation low-pass filtering on the texture profile line based on the Fourier spectrum to obtain a simplified texture profile line.

3. A DEM data filtering system, characterized in that: include: A memory and a processor, wherein the memory stores a computer program executed by the processor, and when the computer program is executed by the processor, the DEM data filtering method according to claim 1 is executed.

4. A storage medium, characterized in that: The storage medium stores a computer program, and the computer program executes the DEM data filtering method according to claim 1 when running.

Images