A DEM Automatic Generation Method Considering Feature Data
By constructing ground lines and feature points in the TIN data, eliminating flat triangles and constructing water system feature lines, the problems of grid value overflow and low DEM accuracy within the water system range are solved, and high-quality digital elevation models are achieved efficiently.
Patent Information
- Application Number
- CN202211047297.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-29
- Publication Date
- 2025-07-25
- Estimated Expiration
- 2042-08-29
AI Technical Summary
When building a digital elevation model, the prior art failed to effectively construct the water system feature line, resulting in overflow of grid values within the water system range and failed to efficiently eliminate flat triangles, affecting the accuracy and production efficiency of DEM.
By constructing ground lines and feature points, the flat triangles are directly found and eliminated from the TIN data, and the water system feature lines are constructed in the reconstructed TIN to make it at the lowest point, generating a digital elevation model.
It improves the accuracy and logic of DEM, avoids the overflow of grid values within the water system, improves production efficiency, and achieves a good overlap between DEM results and contour lines.
Smart Images
Figure CN115359201B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of terrain feature construction, and particularly relates to a method for automatically generating a DEM considering feature data. Background Art
[0002] Digital Elevation Model (DEM for short) is widely used in the fields of surveying and mapping, route design, planning and design, geological engineering, civil engineering, water conservancy construction projects, hydrological analysis, digital battlefield, real scene three-dimensional, digital twin, etc. Using the data such as contour lines, elevation points, water systems, etc. in the Digital Line Graphic (DLG) results to construct an irregular triangular network (TIN) and interpolate to generate DEM has a lower cost and is relatively easy to obtain DEM results.
[0003] In recent years, there are many methods for using the data such as contour lines, elevation points, water systems, etc. in the Digital Line Graphic (DLG) results to construct an irregular triangular network (TIN) and interpolate to generate DEM. However, this method has two problems. First, it does not consider how to construct the water system feature line, and there is a situation where the grid values overflow within the water system range in the generated DEM results, which does not conform to the actual terrain. Second, when constructing the terrain feature line, a loop elimination method for flat triangles is not adopted, and the production efficiency is low. Summary of the Invention
[0004] The purpose of the present invention is to directly search for flat triangles from TIN data, quickly and automatically construct feature line data, specifically eliminate flat triangles, and propose the construction of water system feature lines, so as to make the generated DEM of higher quality and stronger terrain logic, and provide a method for automatically generating a DEM considering feature data.
[0005] In order to achieve the above invention purpose, the embodiments of the present invention provide the following technical solutions:
[0006] A method for automatically generating a DEM considering feature data, comprising the following steps:
[0007] Step S1, constructing a TIN using the data in the Digital Line Graphic results;
[0008] Step S2, constructing terrain feature lines and feature points, eliminating flat triangles in the TIN, and thus reconstructing the TIN;
[0009] Step S3, constructing a water system feature line in the reconstructed TIN to make the water system line at the lowest position;
[0010] Step S4, generating a digital elevation model.
[0011] Furthermore, the data in the Digital Line Graphic results in step S1 includes contour lines, elevation points, and water system data.
[0012] Furthermore, the steps of constructing terrain lines in step S2 to eliminate flat triangles in the TIN and thus reconstruct the TIN include:
[0013] The flat triangles include U-shaped flat triangles;
[0014] According to the structure of the TIN, traverse all non-flat triangles. Taking one side of a non-flat triangle as an adjacent side, search for flat triangles, and so on until an adjacent non-flat triangle is found. The midpoints of the sides of each flat triangle that do not belong to the contour line are used as interpolation points. Connect the vertices of the first and last non-flat triangles with the interpolation points of each flat triangle in sequence to form terrain lines, thereby eliminating the U-shaped flat triangles;
[0015] Obtain the elevation value of the vertex of the first non-flat triangle as H A , and the elevation value of the vertex of the last non-flat triangle as H B , and interpolate the elevation difference between H A and H B according to the distance to calculate the elevation values of the interpolation points of each flat triangle:
[0016]
[0017] where H Vn represents the elevation value of the nth interpolation point, S1 represents the distance between the vertex of the first non-flat triangle and the first interpolation point, and Sn represents the distance between the (n - 1)th interpolation point and the nth interpolation point.
[0018] Furthermore, the steps of constructing feature points in step S2 to eliminate flat triangles in the TIN and thus reconstruct the TIN include:
[0019] The flat triangles include O-shaped flat triangles;
[0020] Take the internal center point M of the closed line in the contour line as a feature point and interpolate it according to the sixteen-direction method. Starting from point M, draw a line segment in the north direction as the starting direction to obtain the intersection points of the line segment and the contour line. Sort all the intersection points by distance, and take the two intersection points with the shortest and the second shortest distances from point M. The elevation value of the shortest intersection point is H A , and the elevation value of the second shortest intersection point is H B ;
[0021] When H A = H B , skip this direction and perform interpolation in the next direction until H A ≠ H B when the interpolation ends, then the elevation value of point M is:
[0022]
[0023] Among them, H M represents the elevation value of point M; the interpolation value takes 0.5 times of the contour interval H A -H B .
[0024] Furthermore, the step of constructing a water system feature line in the reconstructed TIN to make the water system line at the lowest position includes:
[0025] Traverse all triangles in the reconstructed TIN. Based on the triangle with the side coinciding with the water system line, the midpoint of the coinciding side is the starting point, the opposite vertex is the ending point, and the midpoint of the connecting line between the starting point and the ending point is the interpolation point. The elevation value of the starting point is H A , and the elevation value of the ending point is H B ;
[0026] When H A >H B , calculate the elevation value of the interpolation point so that the elevation value of the interpolation point is lower than the elevation value H next of the next contour line below the contour line where the starting point is located:
[0027]
[0028] Among them, H C represents the elevation value of the interpolation point; cor represents the coefficient, and the initial value is taken as 0.5; when H C >H next , cor = cor * 0.5, and loop in turn until H C is lower than H next ;
[0029]
[0030] Among them, represents rounding down, and d represents the contour interval.
[0031] Compared with the prior art, the beneficial effects of the present invention are:
[0032] (1) The present invention extracts topographic data and water system data in DLG data to construct a TIN. After considering feature data, the automatically generated DEM result has high accuracy, and the contour lines generated from the DEM result coincide well with the original contour lines, realizing the simultaneous production of DLG and DEM.
[0033] (2) The present invention finds flat triangles from TIN data, automatically constructs terrain lines and feature points to reconstruct the TIN to eliminate flat triangles, improves the accuracy of the TIN, avoids the problem of low efficiency in constructing feature lines using contour lines, and has high production efficiency.
[0034] (3) In order to represent the characteristics of DEM grids within the water system range, the present invention constructs water system feature lines to ensure that the DEM grid values within the water system range are at the lowest level, while avoiding the situation of grid value overflow within the water system range. Description of the Drawings
[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.
[0036] Figure 1 It is a flowchart of the method of the present invention;
[0037] Figure 2 It is a schematic diagram of constructing a triangular network with contour lines and elevation points of the present invention;
[0038] Figure 3 is a schematic diagram of the flat triangle type of the present invention, where Figure 3(a) is a schematic diagram of a U-shaped flat triangle, and Figure 3(b) is a schematic diagram of an O-shaped flat triangle;
[0039] Figure 4 It is a schematic diagram of constructing terrain lines of the present invention;
[0040] Figure 5 It is a schematic diagram of constructing feature points of the present invention;
[0041] Figure 6 It is a schematic diagram of constructing water system feature lines of the present invention;
[0042] Figure 7 is a comparison diagram before and after eliminating flat triangles of the present invention, where Figure 7(a) is a TIN schematic diagram before eliminating flat triangles, and Figure 7(b) is a TIN schematic diagram after eliminating flat triangles;
[0043] Figure 8 is a schematic diagram of automatically generating terrain lines and water system feature lines of the present invention, where Figure 8(a) is a schematic diagram of automatically generating terrain lines, and Figure 8(b) is a schematic diagram of automatically generating water system feature lines;
[0044] Figure 9 is a schematic diagram of the superposition inspection of the contour lines generated from the DEM data of the present invention and the original contour lines, where Figure 9(a) is a schematic diagram of the superposition of flat ground contour lines, Figure 9(b) is a schematic diagram of the superposition of hilly ground contour lines, Figure 9(c) is a schematic diagram of the superposition of mountainous ground contour lines, and Figure 9(d) is a schematic diagram of the superposition of alpine ground contour lines. Detailed Embodiments
[0045] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.
[0046] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance, or implying any such actual relationship or order between these entities or operations.
[0047] Embodiment 1:
[0048] The present invention is realized through the following technical solutions. As Figure 1 shown, a method for automatically generating a DEM considering feature data includes the following steps:
[0049] Step S1, constructing a TIN using the data in the digital line graphic product.
[0050] The data in the digital line graphic product includes contour lines, elevation points, and water system data. The contour lines and water system data are used as cutting lines. The TIN approximates the terrain surface through continuous triangular faces, which is particularly suitable for terrain data with ridge and valley lines and can well express the landform. Please refer to Figure 2 , the basic process of establishing a TIN is to connect three adjacent data points into an initial triangle, and then use each side of this triangle as a baseline to connect adjacent data points to form new triangles, and so on until all data points have been formed into triangles.
[0051] When establishing a TIN, the elevation points can be directly regarded as discrete points for connection. For the contour lines and water system data, they need to be discretized into points at the nodes and then, together with the elevation points, establish a TIN according to the above method. It should be noted that each triangle cannot cross the contour lines and water system data, that is, the line segment between two nodes of the contour line or water system data must be a side of the triangle.
[0052] Step S2, constructing terrain lines and feature points, eliminating flat triangles in the TIN, and thus reconstructing the TIN.
[0053] As can be seen from the method of establishing the TIN, when only geometric conditions are considered, when the elevation values of the vertices of a triangle are the same, a tiny horizontal plane will be formed, that is, a flat triangle is formed, which does not conform to the actual terrain. According to the terrain difference, two types of flat triangles will be formed. Please refer to Figure 3(a). The first type of flat triangle is mainly generated at the "U"-shaped contour lines, such as ridges, valleys, etc., and is also called the U-shaped flat triangle. Please refer to Figure 3(b). The second type of flat triangle is mainly generated at the "O"-shaped contour lines, such as the top of a mountain, a depression, etc., and is also called the O-shaped flat triangle. Without adding feature data, the constructed TIN does not conform to the actual terrain, resulting in a large gross error in the DEM results generated by interpolation.
[0054] The feature data includes terrain lines, feature points, and water system feature lines. In this scheme, the feature data is used to reconstruct the TIN. Among them, the terrain lines and feature points are mainly used to eliminate the flat triangle problem, and the water system feature lines are mainly used to make the river at the lowest position. In this step, to eliminate the flat triangle, the terrain lines and feature points are used to reconstruct the TIN.
[0055] The U-shaped flat triangle is mainly eliminated by using the terrain line. According to the structure of the TIN, all non-flat triangles are traversed. Taking one side of a non-flat triangle as the adjacent side, a flat triangle is searched, and so on until an adjacent non-flat triangle is found; the midpoints of the sides that do not belong to the contour line in each flat triangle are used as interpolation points, and the vertices of the first and last non-flat triangles are connected to the interpolation points of each flat triangle in turn to form a terrain line, thus eliminating the U-shaped flat triangle.
[0056] For example, please refer to Figure 4 , the first non-flat triangle is , the vertex of the first non-triangle is point A, and the elevation value is H A ; the last non-flat triangle is (since the last non-flat triangle is very small and not shown in Figure 4 ), the vertex of the last non-flat triangle is point B, and the elevation value is H B . The midpoint of the side that does not belong to the contour line in the first found flat triangle is the interpolation point V1, and the midpoint of the side that does not belong to the contour line in the second flat triangle is the interpolation point V2. In fact, one side of the first flat triangle coincides with one side of the second flat triangle.
[0057] Interpolate the elevation difference between H A and H B according to the distance, and calculate the elevation values of the interpolation points of each flat triangle:
[0058]
[0059] Among them, H VnDenote the elevation value of the nth interpolation point, S1 represents the distance between the vertex A of the first non-flat triangle and the first interpolation point V1, and Sn represents the distance between the (n - 1)th interpolation point and the nth interpolation point.
[0060] The O-shaped flat triangle mainly uses feature point elimination, please refer to Figure 5 , take the internal center point M of the closed line in the contour line as the feature point, interpolate it according to the sixteen-direction method, take point M as the starting point, and make a line segment in the north direction as the starting direction to obtain the intersection points of the line segment and the contour line. Sort all the intersection points by distance, and take the two intersection points A and B with the shortest and the second shortest distances from point M. The elevation value of the shortest intersection point A is H A , and the elevation value of the second shortest intersection point B is H B .
[0061] When H A =H B , skip this direction and perform the next direction interpolation until H A ≠H B , then end the interpolation. The elevation value of point M is:
[0062]
[0063] Among them, H M represents the elevation value of point M; the interpolation value takes 0.5 times of the contour interval H A -H B .
[0064] Step S3, construct a water system feature line in the reconstructed TIN to make the water system line at the lowest position.
[0065] Traverse all the triangles in the reconstructed TIN, please refer to Figure 6 , based on the triangle with the side of the triangle coinciding with the water system line, take the midpoint A of the coinciding side as the starting point and the opposite vertex B as the end point. The midpoint C of the connecting line between the starting point and the end point is the interpolation point. The elevation value of the starting point A is H A , and the elevation value of the end point B is H B .
[0066] When H A >H B , calculate the elevation value of the interpolation point C so that the elevation value H C of the interpolation point C is lower than the elevation value H next of the next contour line below the contour line where the starting point A is located:
[0067]
[0068] Among them, H C represents the elevation value of the interpolation point; cor represents the coefficient, and the initial value is taken as 0.5; when H C>H next When cor=cor*0.5, repeat until H C Lower than H next ;
[0069]
[0070] in, It means round down, and d means the equal height interval.
[0071] H next That is, the elevation value of the contour line where the starting point A is located plus the contour line with 1 contour interval, connecting A, B, and C to form a "∧"-shaped characteristic line, which can ensure that the water system characteristic line rises first and then falls.
[0072] Step S4, generating a digital elevation model.
[0073] Based on the initially established TIN, TIN is reconstructed using a large amount of feature data, which can almost eliminate all flat triangles. Figure 7(a) shows the TIN before the flat triangles are eliminated, and Figure 7(b) shows the TIN after the flat triangles are eliminated. At the same time, it also ensures that the position of the water system line is always at the lowest point. Finally, the DEM result is generated by TIN interpolation.
[0074] Embodiment 2:
[0075] This embodiment conducts experimental tests on the basis of the above-mentioned embodiment 1. A 1:10000 unmapped area mapping project in a certain place uses stereo mapping to obtain contour lines and elevation point data, uses DOM as the base map to obtain river and static water body data, and finally generates DEM based on the results of DLG. This experiment selects one map of flat land, hilly land, mountainous land, and high mountainous land, automatically extracts contour lines and elevation points, and interpolates the two-dimensional river edges into three-dimensional lines to ensure that the river flows from top to bottom. Finally, DEM is generated by constructing TIN. In order to verify the reliability of this method, this test uses the reference points to perform accuracy detection on the DEM results.
[0076] The project requires that the mean error of elevation should not exceed the requirements in Table 1, and the maximum error should not exceed 2 times of the mean error. When using contour lines to check the relative accuracy of DEM, the inverted contour lines of DEM data should be superimposed with the original contour lines for inspection, and the deviation of contour lines with the same name should not exceed 1 / 2 of the spacing between adjacent contour lines.
[0077] Table 1. Elevation error of DEM data
[0078] Terrain category Root mean square error of grid point elevation (m) Flat land 2.2 Hilly land 2.2 Mountainous land 3.3 High mountainous land 6.7
[0079] The results of the terrain lines and water system feature lines generated according to this solution are shown as the thick line parts in Figure 8. The thick line part in Figure 8(a) represents the terrain lines, and the thick line part in Figure 8(b) represents the water system feature lines, so as to eliminate flat triangles and make the rivers at the lowest positions.
[0080] The inspection results of the reference points are shown in Table 2. It can be seen that the accuracy of the DEM results generated by this solution meets the requirements.
[0081] Table 2 Accuracy inspection results
[0082] Terrain category Number of check points Root mean square error of elevation (m) Maximum error (m) Flat land 307 0.4 1.1 Hilly land 415 0.9 2.9 Mountainous land 267 0.8 3.5 High mountainous land 261 1.3 4.7
[0083] The contour lines generated by using the DEM data are overlapped and inspected with the original contour lines. As shown in Figures 9(a) and 9(b), the contour lines of flat land and hilly land are sparser, and the overall overlap is better. As shown in Figures 9(c) and 9(d), the contour lines of mountainous land and high mountain land are denser, and the overall overlap is even better. The smoother lines in the figures are the original contour lines, and the less smooth lines are the generated contour lines.
[0084] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Claims
1. A method for automatically generating a DEM considering feature data, characterized in that: Including the following steps: Step S1: Construct a TIN using the data in the digital line graphic results; Step S2: Construct terrain lines and feature points, eliminate the flat triangles in the TIN, and thus reconstruct the TIN; Step S3: Construct water system feature lines in the reconstructed TIN to make the water system lines at the lowest positions; The step of constructing water system feature lines in the reconstructed TIN to make the water system lines at the lowest positions includes: Traverse all the triangles in the reconstructed TIN. Based on the triangles whose sides coincide with the water system lines, take the midpoint of the coincident side as the starting point, the opposite vertex as the ending point, and the midpoint of the connecting line between the starting point and the ending point as the interpolation point, where the elevation value of the starting point is H A , the elevation value of the ending point is H B ; When H A > H B calculate the elevation value of the interpolation point such that the elevation value of the interpolation point is lower than the elevation value H of the next contour line below the contour line where the starting point is located next : Among them, H C represents the elevation value of the interpolation point; cor represents the coefficient, and the initial value is taken as 0.5; when H C >H next , cor = cor * 0.5, and the loop is repeated until H C is lower than H next ; Among them, represents rounding downwards, and d represents the contour interval; Step S4: Generate a digital elevation model.
2. The DEM automatic generation method considering feature data according to claim 1, characterized in that: The data in the digital line graphic results in Step S1 includes contour lines, elevation points, and water system data.
3. The DEM automatic generation method considering feature data according to claim 1, characterized in that: The step of constructing terrain lines, eliminating the flat triangles in the TIN, and thus reconstructing the TIN in Step S2 includes: The flat triangles include U-shaped flat triangles; According to the structure of the TIN, traverse all non-flat triangles, take one side of a non-flat triangle as an adjacent side to find flat triangles, and so on until an adjacent non-flat triangle is found; the midpoints of the sides that do not belong to the contour lines in each flat triangle are used as interpolation points, and the vertices of the head and tail non-flat triangles are sequentially connected to the interpolation points of each flat triangle to form terrain lines, thereby eliminating the U-shaped flat triangles; Obtain the elevation value of the first non-flat triangle vertex as H A , and the elevation value of the last non-flat triangle vertex is H B . Interpolate the elevation difference between H A and H B according to the distance to calculate the elevation values of the interpolation points of each flat triangle: Among them, H Vn represents the elevation value of the nth interpolation point, S1 represents the distance between the vertex of the first non-planar triangle and the first interpolation point, and Sn represents the distance between the (n - 1)th interpolation point and the nth interpolation point.
4. A method for automatically generating a DEM considering feature data according to claim 1, characterized in that: The step of constructing feature points, eliminating the flat triangles in the TIN, and thus reconstructing the TIN in Step S2 includes: The flat triangles include O-shaped flat triangles; Taking the internal center point M of the closed line in the contour line as the feature point, interpolating it according to the sixteen-direction method, taking point M as the starting point, making a line segment in the north direction as the starting direction, obtaining the intersection points of the line segment and the contour line, sorting all the intersection points by distance, and taking the two intersection points with the shortest and the second shortest distances from point M. The elevation value of the shortest intersection point is H A , and the elevation value of the second shortest intersection point is H B ; When H A = H B Skip this direction and perform interpolation in the next direction until H A ≠ H B When the interpolation ends, the elevation value of point M is: Among them, H M represents the elevation value of point M; the interpolation value is taken as 0.5 times of the contour interval H A -H B