Method for extracting main axis of landslide and debris flow

Abstract

The invention discloses a landslide and debris flow main axis extraction method, which comprises the steps of S1, simplifying original boundary graphs of a landslide and a debris flow to obtain simplified graphs; s2, determining a starting point and an ending point of a main axis, and constructing a graph boundary control point set in combination with the simplified graph; s3, performing Deloy internal triangulation on the graph boundary control point set to obtain a triangle set; s4, removing branch triangles in the triangle set to obtain a main skeleton triangle set; s5, extracting a common edge midpoint of the main skeleton triangle set, and constructing a triangle specific median line; and S6, extracting the main axis according to the starting point and the ending point of the main axis and the characteristic median line midpoint of the main skeleton triangle set, effectively extracting the main axis of the landslide and the debris flow by combining multiple algorithms and steps, improving the extraction precision and efficiency, and having important significance for landslide and debris flow research and disaster prevention and reduction.

Description

Technical Field

[0001] The present application relates to the field of image processing technology and the field of geological disasters, and in particular to a method for extracting the main axis of a landslide or a debris flow. Background Art

[0002] Landslides and debris flows are widely-developed types of geological hazards around the world. Their morphological characteristics, especially the main axis characteristics, width variation characteristics, and slope variation characteristics, are of great significance for the dynamic and kinematic analysis of such geomorphic processes. The main axis of a landslide or debris flow indicates the movement path of the landslide or debris flow and measures the movement distance of the landslide or debris flow. At the same time, the measurement of the width and slope of a landslide or debris flow also depends on the determination of the main axis. Therefore, the determination of the main axis of a landslide or debris flow is of great significance for describing the geomorphic characteristics of the landslide or debris flow.

[0003] At present, the main axis of landslides and debris flows is mainly based on manual extraction, that is, it relies on the manual judgment of researchers. This method has large errors, unstable measurement results, and lacks mathematical basis. Although there are some automated algorithms, these algorithms mostly rely on the minimum circumscribed rectangle method or the minimum circumscribed ellipse method. They approximate landslides and debris flows as regular shapes, and finally use the long axis of the regular shape as the main axis of the landslide and debris flow. In general, the results of the above approximate methods are all straight lines, which are relatively simple, but they ignore the complexity of the shapes of landslides and debris flows, and the extraction results are seriously deviated from the real movement path of landslides and debris flows. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for extracting the main axis of landslides and debris flows, which solves the problem that the complexity of the shapes of landslides and debris flows is not considered in the existing extraction methods, and the extraction results seriously deviate from their actual movement paths.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for extracting the main axis of a landslide or a debris flow, comprising: S1. Simplify the original boundary graphics of landslide and debris flow to obtain simplified graphics; S2. Determine the starting point and end point of the main axis, and construct a set of control points of the graphic boundary in combination with the simplified graphic; S3, performing Delaunay triangulation on the control point set of the graphic boundary to obtain a triangle set; S4, removing branch triangles from the triangle set to obtain a main skeleton triangle set; S5, extracting the midpoints of the common edges of the main skeleton triangle set and constructing a specific median line of the triangle; S6. Extract the main axis according to the starting point and end point of the main axis and the midpoint of the characteristic median of the main skeleton triangle set.

[0006] Further: S1 includes: S11, extracting the vertex coordinates of the original boundary graph of the landslide and debris flow; S12. Calculate the geometric center of the original boundary figure based on the vertices of the original boundary figure , whose expression is:

[0007] in, and are the vertices of the original boundary shape; i Indicates the number of vertices, N Represents the total number of vertices; A Represents the original boundary graphic area; S13. Construct the covariance matrix of the original boundary graph according to the vertex coordinates and geometric center of the original boundary graph Cov , whose expression is:

[0008] in, express x The variance of the coordinates, express x Coordinates and y The covariance of the coordinates, express y Coordinates and x The covariance of the coordinates, express y Variance of coordinates; S14, calculating the eigenvalues ​​of the covariance matrix of the original boundary graphic; S15, appropriately expanding the equivalent ellipse corresponding to the original boundary figure in the main direction and the secondary direction to a coverage standard of 95% of the data, and obtaining the major axis L1 and the minor axis L2 of the equivalent ellipse; S16. According to the minor axis L2 of the equivalent ellipse, the Douglas Peucker algorithm is used to simplify the original boundary figure to obtain a simplified figure.

[0009] Further: S2 includes: S21, extracting the boundary line of the original boundary figure, and constructing 100 construction points at equal intervals on the boundary line of the original boundary figure as the point set PG1; S22, determining the highest point and the lowest point in the point set PG1 through the digital elevation map, and using them as the starting point P1 and the end point P2 of the main axis respectively; S23, extracting vertices of the simplified graph as point set PG2; S24, delete the points in the point set PG2 whose distance to the starting point P1 or the end point P2 is less than L1 / 50, and merge the remaining points in PG2 after deletion with the starting point P1 and the end point P2 as the graphic boundary control point set PG3.

[0010] Further: S3 includes: S31, performing Delaunay triangulation on the control point set of the graphic boundary to obtain an original triangle set TIN1; S32. Extract triangles in the triangle set TIN1 that are within the range of the simplified graphics as the triangle set TIN2.

[0011] Further: S4 includes: S41, finding the endpoints of all triangles in the triangle set TIN2, and deleting the triangles where the independent endpoints are located, to obtain a deleted triangle set; S42, taking the deleted triangle set as a new triangle set TIN2, and returning to S41; S43. Repeat S41-S42 until there are no independent endpoints, and use the remaining triangles as main skeleton triangles.

[0012] Further: In S41, the independent endpoint represents a point that is not an intersection point of multiple triangles and does not overlap with the starting point P1 or the end point P2.

[0013] Further: In S5, the method for the median of the main skeleton triangle set is: extract the midpoints of the common edges of all the main skeleton triangles in the main skeleton triangle set, and construct a specific median of the main skeleton triangle based on the common edge midpoints.

[0014] Further: S6 includes: S61, sequentially constructing the midpoints of all common edges of the main skeleton triangle set; S62. Connect the starting point, the midpoint of the specific median line and the end point in sequence to obtain the main axis.

[0015] The beneficial effects of the present invention are: 1. Compared with the extraction of main axis using three-dimensional elevation data, the present invention proposes a main axis extraction method based on Delaunay triangulation of landslide and debris flow plane morphology, which has a clearer mathematical basis, a simpler data structure to be processed, and a higher computational efficiency; 2. Compared with the traditional skeleton line extraction method, which needs to find the main skeleton line through hierarchical analysis and backtracking, the present invention proposes a method of first deleting the branch structure and then extracting the main axis according to the characteristics of landslide and debris flow geomorphic processes, thus realizing a more efficient and accurate extraction method; 3. Compared with the traditional skeleton line extraction method, in which the skeleton line bending points are sharp and protruding, the method of the present invention forms a smoother main axis, avoiding inappropriate and overly sharp main axis angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the flow chart of the main axis extraction method for landslides and debris flows.

[0017] Figure 2 This is a schematic diagram of simplifying the original boundary graphics.

[0018] Figure 3 A schematic diagram for constructing a set of control points for the graphic boundary.

[0019] Figure 4 A schematic diagram for obtaining a triangle collection.

[0020] Figure 5 Schematic diagram for extracting the main axis. DETAILED DESCRIPTION

[0021] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0022] like Figure 1 As shown, in one embodiment of the present invention, a method for extracting the main axis of a landslide or a debris flow is provided, comprising: S1. Simplify the original boundary graphics of landslide and debris flow to obtain simplified graphics; S2. Determine the starting point and end point of the main axis, and construct a set of control points of the graphic boundary in combination with the simplified graphic; S3, performing Delaunay triangulation on the control point set of the graphic boundary to obtain a triangle set; S4, removing branch triangles from the triangle set to obtain a main skeleton triangle set; S5, extracting the midpoints of the common edges of the main skeleton triangle set and constructing a specific median line of the triangle; S6. Extract the main axis according to the starting point and end point of the main axis and the midpoint of the characteristic median of the main skeleton triangle set.

[0023] Specifically, S1 includes: S11, extracting the vertex coordinates of the original boundary graph of the landslide and debris flow; In particular, the vertices of the simplified graph S2 include ,in and Coincident, point set PG1 includes ; S12. Calculate the geometric center of the original boundary figure based on the vertices of the original boundary figure , whose expression is:

[0024] in, and are the vertices of the original boundary shape; i Indicates the number of vertices, N Represents the total number of vertices; A Represents the original boundary graphic area; S13. Construct the covariance matrix of the original boundary graph according to the vertex coordinates and geometric center of the original boundary graph Cov , whose expression is:

[0025] in, express x The variance of the coordinates, express x Coordinates and y The covariance of the coordinates, express y Coordinates and x The covariance of the coordinates, express y Variance of coordinates; S14, calculating the eigenvalues ​​of the covariance matrix of the original boundary graphic; In this embodiment, the formula Solve the eigenvalues ​​and eigenvectors of the covariance matrix respectively to obtain the eigenvalues ​​of the covariance matrix and ; Among them, det(.) represents the operation of calculating the determinant, I is the identity matrix; S15. Appropriately expand the equivalent ellipse corresponding to the original boundary figure in the main direction and the secondary direction to the data coverage standard of 95%, and obtain the major axis L1 and the minor axis L2 of the equivalent ellipse, which are expressed as follows:

[0026] S16. According to the minor axis L2 of the equivalent ellipse, the Douglas Peucker algorithm is used to simplify the original boundary graph to obtain a simplified graph; specifically, in this embodiment, L2 / 20 is used as the tolerance.

[0027] In this embodiment, the original boundary graph is named S1, the simplified graph is named S2, and the schematic diagram of simplifying S1 to S2 is as follows: Figure 2 shown.

[0028] Specifically, Figure 3 As shown, S2 includes: S21, extracting the boundary line of the original boundary figure, and constructing 100 construction points at equal intervals on the boundary line of the original boundary figure as the point set PG1; S22, determining the highest point and the lowest point in the point set PG1 through the digital elevation map, and using them as the starting point P1 and the end point P2 of the main axis respectively; S23, extracting vertices of the simplified graph as point set PG2; In particular, the vertices of the simplified graph S2 include ,in and Coincident, point set PG2 includes ; S24, delete the points in the point set PG2 whose distance to the starting point P1 or the end point P2 is less than L1 / 50, and merge the remaining points after the deletion with the starting point P1 and the end point P2 as the graphic boundary control point set PG3.

[0029] like Figure 4 As shown, S3 includes: S31, performing Delaunay triangulation on the control point set of the graphic boundary to obtain an original triangle set TIN1; S32. Extract triangles in the triangle set TIN1 that are within the range of the simplified graphics as the triangle set TIN2.

[0030] S4 includes: S41, finding the endpoints of all triangles in the triangle set TIN2, and deleting the triangles where the independent endpoints are located, to obtain a deleted triangle set; The independent endpoints represent points that are not intersection points of multiple triangles and do not coincide with the starting point P1 or the end point P2; S42, taking the deleted triangle set as a new triangle set TIN2, and returning to S41; S43. Repeat S41-S42 until there are no independent endpoints, and use the remaining triangles as main skeleton triangles.

[0031] In particular, suppose the main skeleton triangle where the main axis starting point P1 is located is numbered TIN3-1, find the triangle that shares the same side as the TIN3-1 triangle, define the latter triangle as TIN3-2, and continue to find triangles that intersect with TIN3-2, and number them in sequence until all main skeleton triangles are numbered. The main axis end point P2 should be on the last triangle TIN3-n.

[0032] In S5, the method for the median of the main skeleton triangle set is: extract the midpoints of the common edges of all the main skeleton triangles in the main skeleton triangle set, and construct a specific median of the main skeleton triangle based on the common edge midpoints. like Figure 5 As shown, S6 includes: S61, sequentially constructing the midpoints of all common edges of the main skeleton triangle set; S62. Connect the starting point, the midpoint of the specific median line and the end point in sequence to obtain the main axis.

[0033] Specifically, in this embodiment, it can be described as: Find the specific median lines of the main skeleton triangles as LG1-1 to LG1-(n-2), and find the midpoints of these line segments respectively. Each midpoint is defined as PG5-2 to PG5-(n-1) according to the number of the triangle in which it is located; After connecting the starting point P1 and PG5-2 of the main axis, connect PG5-2, PG5-3, PG5-(n-1) in sequence, and finally connect PG5-(n-1) and the end point P2 of the main axis. The result of this connection is the main axis of the landslide and debris flow.

[0034] This application uses two-dimensional graphics to obtain the central axis of landslides and debris flows, which is particularly suitable for cases where the elevation changes are not obvious and the aspect ratio (the ratio of the length to the width of the landslide or debris flow) is small. The method of using the characteristics of landslides and debris flows (starting point and end point) to first remove the branch structure and retain the main skeleton structure and then extract the main axis can effectively improve the calculation efficiency and result accuracy.

[0035] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for extracting the main axis of a landslide or debris flow, characterized in that: include: S1. Simplify the original boundary graphics of landslide and debris flow to obtain simplified graphics; S2. Determine the starting point and end point of the main axis, and construct a set of control points of the graphic boundary in combination with the simplified graphic; S3, performing Delaunay triangulation on the control point set of the graphic boundary to obtain a triangle set; S4, removing branch triangles from the triangle set to obtain a main skeleton triangle set; S5, extracting the midpoints of the common edges of the main skeleton triangle set and constructing a specific median line of the triangle; S6. Extract the main axis according to the starting point and end point of the main axis and the midpoint of the characteristic median of the main skeleton triangle set.

2. The method for extracting the main axis of a landslide or debris flow according to claim 1, characterized in that: S1 includes: S11, extracting the vertex coordinates of the original boundary graph of the landslide and debris flow; S12. Calculate the geometric center of the original boundary figure based on the vertices of the original boundary figure , whose expression is: in, and are the vertices of the original boundary shape; i Indicates the number of vertices, N Represents the total number of vertices; A Represents the original boundary graphic area; S13. Construct the covariance matrix of the original boundary graph according to the vertex coordinates and geometric center of the original boundary graph Cov , whose expression is: in, express x The variance of the coordinates, express x Coordinates and y The covariance of the coordinates, express y Coordinates and x The covariance of the coordinates, express y Variance of coordinates; S14, calculating the eigenvalues ​​of the covariance matrix of the original boundary graphic; S15, appropriately expanding the equivalent ellipse corresponding to the original boundary figure in the main direction and the secondary direction to a coverage standard of 95% of the data, and obtaining the major axis L1 and the minor axis L2 of the equivalent ellipse; S16. According to the minor axis L2 of the equivalent ellipse, the Douglas Peucker algorithm is used to simplify the original boundary figure to obtain a simplified figure.

3. The main axis extraction method of landslide and debris flow according to claim 1, characterized in that S2 include: S21, extracting the boundary line of the original boundary figure, and constructing 100 construction points at equal intervals on the boundary line of the original boundary figure as the point set PG1; S22, determining the highest point and the lowest point in the point set PG1 through the digital elevation map, and using them as the starting point P1 and the end point P2 of the main axis respectively; S23, extracting vertices of the simplified graph as point set PG2; S24, delete the points in the point set PG2 whose distance to the starting point P1 or the end point P2 is less than L1 / 50, and merge the remaining points in PG2 after deletion with the starting point P1 and the end point P2 as the graphic boundary control point set PG3.

4. The method for extracting the main axis of a landslide or a debris flow according to claim 1, characterized in that S3 include: S31, performing Delaunay triangulation on the control point set of the graphic boundary to obtain an original triangle set TIN1; S32. Extract triangles in the triangle set TIN1 that are within the range of the simplified graphics as the triangle set TIN2.

5. The method for extracting the main axis of a landslide or debris flow according to claim 1, characterized in that: S4 includes: S41, finding the endpoints of all triangles in the triangle set TIN2, and deleting the triangles where the independent endpoints are located, to obtain a deleted triangle set; S42, taking the deleted triangle set as a new triangle set TIN2, and returning to S41; S43. Repeat S41-S42 until there are no independent endpoints, and use the remaining triangles as main skeleton triangles.

6. The method for extracting the main axis of a landslide or debris flow according to claim 5, characterized in that: In S5 and S41 , the independent endpoints represent points that are not intersection points of multiple triangles and do not overlap with the starting point P1 or the end point P2 .

7. The method for extracting the main axis of a landslide or debris flow according to claim 5, characterized in that: In S5, the method for determining the median of the main skeleton triangle set is: extracting the midpoints of the common edges of all the main skeleton triangles in the main skeleton triangle set, and constructing a specific median of the main skeleton triangle based on the common edge midpoints.

8. The method for extracting the main axis of a landslide or a debris flow according to claim 5, characterized in that S6 include: S61, sequentially constructing the midpoints of all common edges of the main skeleton triangle set; S62. Connect the starting point, the midpoint of the specific median line and the end point in sequence to obtain the main axis.

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