A method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing

Abstract

The present invention relates to a method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing, comprising the following steps: 1) obtaining close-up photogrammetric data of a project area; 2) constructing a high-precision three-dimensional real-scene model; 3) extracting the spatial coordinates of characteristic points at the outer boundaries of the dangerous rock mass; 4) calculating the spatial coordinates of characteristic points at the inner boundaries of the dangerous rock mass; and 5) obtaining the volume parameters of the dangerous rock mass. The method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing effectively overcomes the deficiency of traditional aerial surveying technology, which can only collect data in the vertical direction. It is more suitable for areas with large terrain undulations. Furthermore, it obtains refined three-dimensional information of the dangerous rock mass through close-up photogrammetry, thereby obtaining more accurate volume parameters of the dangerous rock mass.

Description

Technical Field

[0001] The present invention belongs to the technical field of dangerous rockfall hazard assessment, and in particular to a method for acquiring volume parameters of dangerous rock masses based on low-altitude remote sensing. Background Art

[0002] Dangerous rock masses are one of my country's three major geological hazards. They often occur on steep rock slopes, are hidden and sudden, and have become a major source of hazard for engineering construction in mountainous areas. Therefore, assessing the hazard of dangerous rock masses is of great practical significance. The volume of dangerous rock masses is a key parameter in hazard assessment and plays a crucial role. Traditional methods for determining the volume of dangerous rock masses rely primarily on on-site measurements. However, due to terrain factors, manual measurement is often difficult to implement, poses safety risks, and is inefficient. In recent years, several non-contact measurement methods have emerged, including aerial photogrammetry, 3D geological modeling, and 3D laser scanning. Aerial photogrammetry, limited to vertical data acquisition and limited to vertical altitude, lacks the ability to capture three-dimensional information, making it difficult to accurately extract dangerous rock mass volume parameters. 3D geological modeling requires a large amount of basic data, complex processing procedures, and high hardware requirements, making it difficult to widely promote. 3D laser scanning offers high accuracy and convenient data processing, but is relatively expensive. Therefore, there is an urgent need to develop a cost-effective method for determining dangerous rock mass volume parameters to meet the needs of various engineering construction projects. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for obtaining the volume parameters of dangerous rock masses based on low-altitude remote sensing. The method uses close-up oblique photography technology to collect images of dangerous rocks in the engineering area, and simultaneously obtains the terrain data of the engineering area. A high-precision three-dimensional real-scene model is constructed based on the images and terrain data, and the volume parameters of dangerous rocks are obtained through spatial calculation for dangerous rock hazard assessment.

[0004] The present invention solves the technical problem by the following technical solutions:

[0005] A method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing, characterized in that the method comprises the following steps:

[0006] Step 1) Obtain photogrammetric data close to the project area:

[0007] ① Designate the engineering area with dangerous rock masses as the low-altitude remote sensing data collection area;

[0008] ② Collecting terrain data of the project area: Using the UAV real-time differential positioning method (RTK) to collect basic terrain information data of the project area, and obtain basic terrain information of the project area;

[0009] ③ Plan UAV routes: Based on the basic terrain information data of the project area, plan UAV routes to ensure that the heading overlap of UAVs reaches 95% and the lateral overlap reaches 85%;

[0010] ④ Carry out UAV close-up oblique photography: Use UAV close-up oblique photography to obtain close-up photogrammetric data of the project area;

[0011] Step 2) Constructing a high-precision 3D real-scene model: Processing the close-up photogrammetry data of the project area obtained in step 1) to obtain a high-precision digital orthophoto and a digital elevation model, and constructing a high-precision 3D real-scene model;

[0012] Step 3) Extracting the spatial coordinates of the outer boundary feature points of the dangerous rock body: Based on the high-precision three-dimensional real-scene model constructed in step 2), extract the spatial coordinates of the six outer boundary feature points of the dangerous rock body:

[0013] ① Extract the spatial coordinates of the four outer boundary feature points on the surface of the dangerous rock mass, where the spatial coordinates of boundary feature point 1 are marked as (x1, y1, z1), the spatial coordinates of boundary feature point 2 are marked as (x2, y2, z2), the spatial coordinates of boundary feature point 3 are marked as (x3, y3, z3), and the spatial coordinates of boundary feature point 4 are marked as (x4, y4, z4);

[0014] ② Extract the spatial coordinates of two feature points adjacent to the parent rock at the bottom of the dangerous rock mass: the spatial coordinates of boundary feature point 5 are marked as (x5, y5, z5), and the spatial coordinates of boundary feature point 6 are marked as (x6, y6, z6);

[0015] Step 4) Calculate the spatial coordinates of the boundary feature points inside the dangerous rock body: Based on the spatial coordinates of the boundary feature points outside the dangerous rock body extracted in step 3), calculate the spatial coordinates of the boundary feature points inside the dangerous rock body:

[0016] Select two characteristic points where the bottom of the dangerous rock mass meets the parent rock as the inner boundary characteristic points of the dangerous rock mass. The spatial coordinates of the inner boundary characteristic point 7 are marked as (x7, y7, z7), and the spatial coordinates of the inner boundary characteristic point 8 are marked as (x8, y8, z8);

[0017] Calculate the spatial coordinates of the inner boundary feature points according to formula (1):

[0018]

[0019] 5) Obtaining the volume parameters of the dangerous rock mass: Based on the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps 3) and 4), a spatial geometric model of the dangerous rock mass is established, and the volume parameters of the dangerous rock mass are calculated:

[0020] The six outer boundary feature points and two inner boundary feature points on the surface of the dangerous rock mass form an irregular space hexahedron that can completely envelop the dangerous rock mass. The volume of the irregular space hexahedron is calculated to obtain the volume parameters of the dangerous rock mass.

[0021] Moreover, the volume parameter calculation process of the dangerous rock mass obtained by the volume of the irregular space hexahedron is:

[0022] The irregular spatial hexahedron is divided into five tetrahedrons. According to the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps S3 and S4, the volume of each tetrahedron is calculated, and the volume of the spatial hexahedron is obtained by cumulative summation: wherein the volume of the tetrahedron is calculated using formulas (2) to (6):

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] In formulas (2) to (6), V i (i=1,2,3,4,5) is the volume of the five tetrahedrons after segmentation, (x j ,y j ,z j )(j=1,2,3,4,5,6) are the spatial coordinates of the feature points of the tetrahedron to be determined. After obtaining the volumes of the five tetrahedrons, the volume of the spatial hexahedron is obtained by cumulative summation, as shown in formula (7):

[0029]

[0030] Where V is the volume of the space hexahedron;

[0031] Calculate the volume of the irregular space hexahedron and obtain the volume parameters of the dangerous rock mass.

[0032] Furthermore, the step 2) processes the close-up photogrammetry data of the project area obtained in step 1) to obtain a high-precision digital orthophoto and a digital elevation model. The specific method for constructing a high-precision three-dimensional real scene model includes the following steps:

[0033] ① Create digital orthophotos: Based on the photogrammetric data of the project area obtained in step 1), geometric correction is performed on the images using internal and external orientation elements and image control points to generate high-precision digital orthophotos.

[0034] ② Create a digital elevation model (DEM): Based on the digital aerial triangulation method, the coordinates of the image points measured on the photos and the coordinates of a small number of field control points are solved indoors to obtain the plane and elevation coordinates of the infill points. This provides absolute directional control points for mapping in areas lacking field control points. Based on the obtained 3D coordinates of the infill points, spatial interpolation processing is performed to obtain a high-precision DE for the project area.

[0035] ③ Create a 3D real-life model: Divide the high-precision digital orthophotos and high-precision DEM of the project area created in the above steps into multiple regional blocks. Send the digital orthophotos of one regional block and the high-precision DEM of the project area to the oblique photogrammetry system. Overlay the digital orthophotos on the DEM surface to generate a high-precision 3D real-life model of one regional block. Process them sequentially to obtain high-precision 3D real-life models of each regional block, and then perform splicing and integration processing to obtain a high-precision 3D real-life model of the project area.

[0036] Furthermore, if the bottom of the dangerous rock mass is not exposed, the spatial coordinates of the boundary feature points 5 and 6 can be calculated by the distance between the surface of the dangerous rock mass and the parent rock, including the following steps:

[0037] ① Measure the distance h between the surface of the dangerous rock mass and the parent rock: Rotate the 3D real scene model to the side of the dangerous rock mass, explore the structural surface between the dangerous rock mass and the parent rock, and measure the distance from the surface of the dangerous rock mass to the structural surface, which is the distance h between the surface of the dangerous rock mass and the parent rock;

[0038] ② Calculate the coordinates of boundary feature points 5 and 6. Feature point 5 can be generalized as the projection point of feature point 3 on the parent rock, with coordinates marked as (x5, y5, z5), and the value is equivalent to (x3-h, y3, z3). Feature point 6 can be generalized as the projection point of feature point 4 on the parent rock, with coordinates marked as (x6, y6, z6), and the value is equivalent to (x6-h, y6, z6).

[0039] The advantages and beneficial effects of the present invention are:

[0040] 1. The present invention's method for obtaining dangerous rock mass volume parameters based on low-altitude remote sensing can not only calculate the volume of dangerous rock masses separated from their parent bodies, but also obtain volume parameters of dangerous rock masses that have not separated from their parent bodies, which is difficult to achieve with other methods. In engineering practice, dangerous rock masses are often embedded in their parent bodies, making this method highly applicable in engineering projects. It can effectively save manpower and material resources, improve work efficiency, and provide calculation parameters for dangerous rock mass stability assessment.

[0041] 2. The method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing of the present invention effectively overcomes the deficiency of traditional aerial survey technology that can only collect vertical data. It is more suitable for areas with large terrain undulations, and obtains refined three-dimensional information of dangerous rock masses through close-up photography, thereby obtaining more accurate volume parameters of dangerous rock masses.

[0042] 3. The dangerous rock volume calculation method adopted by the present invention has the characteristics and advantages of rigorous mathematical logic, simple calculation formula and low operation difficulty. At this stage, the dangerous rock volume measurement method based on the model either has high calculation complexity (complex mathematical formula) or the volume characterization is not accurate enough (rough geometric model), resulting in unsatisfactory results. This method comprehensively considers the objective reality of the changeable spatial form of dangerous rock bodies, and fits the dangerous rocks through hexahedrons. It is only necessary to select the eight vertices that envelop the dangerous rock body in sequence in the three-dimensional model and record the corresponding coordinates, and finally input the formula. The present invention has achieved a good balance between the calculation complexity and the accurate measurement of the dangerous rock volume, which not only reduces the field measurement work, but also does not affect the scientific nature of the subsequent rock mass hazard assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of a method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing according to the present invention;

[0044] Figure 2a Schematic diagram of the selection of boundary feature points for the high-precision three-dimensional real-scene model of the present invention (the bottom of the dangerous rock mass is exposed, and boundary feature points 5 and 6 are exposed);

[0045] Figure 2b Schematic diagram of selecting boundary feature points of the high-precision three-dimensional real scene model of the present invention (the bottom of the dangerous rock mass is not exposed, and boundary feature points 5 and 6 are not exposed);

[0046] Figure 3 It is a high-precision three-dimensional real-scene model. DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0048] A method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing, the method comprising the following steps:

[0049] Step 1) Obtain photogrammetric data close to the project area:

[0050] ① Designate the engineering area with dangerous rock masses as the low-altitude remote sensing data collection area;

[0051] ② Collecting terrain data of the project area: Performing drone remote sensing differential terrain measurement on the low-altitude remote sensing data collection area. In this embodiment, a drone real-time differential positioning method (RTK) is used to collect basic terrain information data of the project area to obtain basic terrain information of the project area;

[0052] ③ Plan UAV routes: Based on the basic terrain information data of the project area, plan UAV routes to ensure that the heading overlap of UAVs reaches 95% and the lateral overlap reaches 85%;

[0053] ④ Carry out UAV close-up oblique photography: Use UAV close-up oblique photography to obtain close-up photogrammetry data of the project area. For areas with excessive geometric distortion or focus failure caused by terrain undulations, manually control the UAV to take additional photos.

[0054] Step 2) Constructing a high-precision 3D real-scene model: Processing the close-up photogrammetry data of the project area obtained in step 1) to obtain a high-precision digital orthophoto and digital elevation model, and constructing a high-precision 3D real-scene model, including the following steps:

[0055] ① Create digital orthophotos: Based on the photogrammetric data of the project area obtained in step 1), geometric correction is performed on the images using internal and external orientation elements and image control points to generate high-precision digital orthophotos.

[0056] ② Create a digital elevation model (DEM): Based on the digital aerial triangulation method, the coordinates of the image points measured on the photos and the coordinates of a small number of field control points are solved indoors to obtain the plane and elevation coordinates of the infill points. This provides absolute directional control points for mapping in areas lacking field control points. Based on the three-dimensional coordinates of the infill points, spatial interpolation processing is performed to obtain a high-precision DEM of the project area.

[0057] ③ Create a 3D real-life model: Divide the high-precision digital orthophotos and DEM created in the above steps into multiple regional blocks, send the digital orthophotos and DEM of one regional block to the oblique photogrammetry system, overlay the digital orthophotos onto the DEM surface, and generate a high-precision 3D real-life model of one regional block; process them sequentially to obtain high-precision 3D real-life models of each regional block, and then perform splicing and integration processing to obtain a high-precision 3D real-life model of the project area.

[0058] Step 3) Extracting the spatial coordinates of the outer boundary feature points of the dangerous rock body: Based on the high-precision three-dimensional real-scene model constructed in step 2), extract the spatial coordinates of the six outer boundary feature points of the dangerous rock body:

[0059] ① Extract the spatial coordinates of the four outer boundary feature points on the surface of the dangerous rock mass: Based on the high-precision three-dimensional real-scene model constructed in step 2), the four outer boundary feature points of the dangerous rock mass are delineated through human-computer interactive remote sensing interpretation. Among them, boundary feature points 1 and 2 are the intersection points of two joint fracture lines and the outer facade of the dangerous rock side, and boundary feature points 3 and 4 are the intersection points of the three outer facades of the dangerous rock. The spatial coordinates of boundary feature point 1 are marked as (x1, y1, z1), the spatial coordinates of boundary feature point 2 are marked as (x2, y2, z2), the spatial coordinates of boundary feature point 3 are marked as (x3, y3, z3), and the spatial coordinates of boundary feature point 4 are marked as (x4, y4, z4); x is the latitude information, y is the longitude information, and z is the elevation information.

[0060] ② Extract the spatial coordinates of two feature points adjacent to the bottom of the dangerous rock mass and the parent rock: The bottom of the dangerous rock mass is affected by weathering, joints, etc., and is generally exposed to the outside. It can be extracted in the high-precision 3D real-scene model. Based on the high-precision 3D real-scene model constructed in step 2), by adjusting the model perspective and human-computer interactive interpretation, the two feature points adjacent to the bottom of the dangerous rock mass and the parent rock are circled, namely the intersection points of the downward facade of the dangerous rock and the two joint crack lines. The spatial coordinates of boundary feature point 5 are marked as (x5, y5, z5), and the spatial coordinates of boundary feature point 6 are marked as (x6, y6, z6). Figure 2a ;

[0061] If the bottom of the dangerous rock mass is not exposed, the spatial coordinates of the boundary feature points 5 and 6 can be calculated by the distance between the surface of the dangerous rock mass and the parent rock. First, measure the distance h between the surface of the dangerous rock mass and the parent rock. Rotate the three-dimensional real-scene model to the side of the dangerous rock mass, explore the structural surface between the dangerous rock mass and the parent rock, and measure the distance from the surface of the dangerous rock mass to the structural surface, which is the distance h between the surface of the dangerous rock mass and the parent rock; secondly, calculate the coordinates of the boundary feature points 5 and 6. Feature point 5 can be generalized as the projection point of feature point 3 on the parent rock, with coordinates marked as (x5, y5, z5), and the value is equivalent to (x3-h, y3, z3). Feature point 6 can be generalized as the projection point of feature point 4 on the parent rock, with coordinates marked as (x6, y6, z6), and the value is equivalent to (x6-h, y6, z6), see Figure 2b .

[0062] The coordinate information of the four outer boundary feature points on the surface of the dangerous rock mass and the two feature points adjacent to the parent rock at the bottom of the dangerous rock mass extracted in the above steps are combined to form the spatial coordinates of the six outer boundary feature points of the dangerous rock mass.

[0063] Step 4) Calculate the spatial coordinates of the boundary feature points inside the dangerous rock body: Based on the spatial coordinates of the boundary feature points outside the dangerous rock body extracted in step 3), calculate the spatial coordinates of the boundary feature points inside the dangerous rock body:

[0064] Select two feature points where the bottom of the dangerous rock mass meets the parent rock as the inner boundary feature points of the dangerous rock mass. The spatial coordinates of the inner boundary feature point 7 are marked as (x7, y7, z7), and the spatial coordinates of the inner boundary feature point 8 are marked as (x8, y8, z8). It is impossible to directly extract their spatial coordinates from the three-dimensional real-life model. They need to be calculated based on the spatial coordinates of the outer boundary feature points of the dangerous rock mass extracted in step S3. Based on step 3), the spatial coordinates of the outer boundary feature points of the dangerous rock mass are extracted and the spatial coordinates of the inner boundary feature points of the dangerous rock mass are calculated. According to the spatial relationship of the boundary feature points of the dangerous rock mass,

[0065] Calculate the spatial coordinates of the inner boundary feature points according to formula (1):

[0066]

[0067] 5) Obtaining the volume parameters of the dangerous rock mass: Based on the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps 3) and 4), a spatial geometric model of the dangerous rock mass is established, and the volume parameters of the dangerous rock mass are calculated:

[0068] The six outer boundary feature points and two inner boundary feature points on the surface of the dangerous rock mass form an irregular space hexahedron that can completely envelop the dangerous rock mass. The volume of the irregular space hexahedron is calculated to obtain the volume parameters of the dangerous rock mass.

[0069] Since the volume of the hexahedron cannot be directly calculated, it is divided into five tetrahedrons. The volume of the irregular hexahedron is used to obtain the volume parameters of the dangerous rock mass. The calculation process is as follows:

[0070] The irregular spatial hexahedron is divided into five tetrahedrons. According to the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps S3 and S4, the volume of each tetrahedron is calculated, and the volume of the spatial hexahedron is obtained by cumulative summation: wherein the volume of the tetrahedron is calculated using formulas (2) to (6):

[0071]

[0072]

[0073]

[0074]

[0075]

[0076] In formulas (2) to (6), V i (i=1,2,3,4,5) is the volume of the five tetrahedrons after segmentation, (x j ,y j ,z j)(j=1,2,3,4,5,6) are the spatial coordinates of the feature points of the tetrahedron to be determined. After obtaining the volumes of the five tetrahedrons, the volume of the spatial hexahedron is obtained by cumulative summation, as shown in formula (7):

[0077]

[0078] Where V is the volume of the space hexahedron;

[0079] Calculate the volume of the irregular space hexahedron and obtain the volume parameters of the dangerous rock mass.

[0080] by Figure 3 Take the volume calculation of the dangerous rock mass shown in as an example, the calculation process is as follows:

[0081] 1) Extract the spatial coordinates of the boundary feature points outside the dangerous rock body:

[0082] ① First, extract the spatial coordinates of the four outer boundary feature points on the surface of the dangerous rock mass in the three-dimensional model:

[0083] Feature point 1: (x1, y1, z1) = (726.45, 980.26, 297.48)

[0084] Feature point 2: (x2, y2, z2) = (708.40, 983.31, 291.53)

[0085] Feature point 3: (x3, y3, z3) = (709.18, 981.99, 273.68)

[0086] Feature point 4: (x4, y4, z4) = (727.41, 974.07, 284.73)

[0087] ② Secondly, extract the spatial coordinates of two feature points adjacent to the parent rock at the bottom of the dangerous rock mass:

[0088] Feature point 5: (x5, y5, z5) = (724.04, 994.46, 320.70)

[0089] Feature point 6: (x6, y6, z6) = (703.92, 999.84, 309.69)

[0090] The coordinate information of the four outer boundary feature points on the surface of the dangerous rock mass and the two feature points adjacent to the parent rock at the bottom of the dangerous rock mass extracted in the above steps are combined to form the spatial coordinates of the six outer boundary feature points of the dangerous rock mass.

[0091] 2) Calculate the spatial coordinates of the boundary feature points of the dangerous rock body:

[0092] Two characteristic points where the bottom of the dangerous rock mass meets the parent rock are selected as the inner boundary characteristic points of the dangerous rock mass, namely: the projection of boundary characteristic points 5 and 6 on the vertical parent rock surface, the spatial coordinates of the inner boundary characteristic point 7 are marked as (x7, y7, z7), and the spatial coordinates of the inner boundary characteristic point 8 are marked as (x8, y8, z8); according to formula (1), the following can be obtained:

[0093] Feature point 7: (x7, y7, z7) = (x6, y6, z6) - (x2, y2, z2) + (x3, y3, z3) = (704.7, 998.52, 291.84)

[0094] Feature point 8: (x8, y8, z8) = (x5, y5, z5) - (x1, y1, z1) + (x4, y4, z4) = (725.0, 988.27, 307.95)

[0095] 3) Obtain volume parameters of dangerous rock mass

[0096] According to the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps 1) and 2), a spatial geometric model of the dangerous rock mass is established, and the volume parameters of the dangerous rock mass are calculated: According to formulas (2) to (7), the coordinate data are substituted into the dangerous rock mass volume to calculate.

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103] After calculation, Figure 3 The volume of the dangerous rock on display is 3365.049m 3 .

[0104] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing, characterized by: The acquisition method comprises the following steps: Step 1) Obtain photogrammetric data close to the project area: ① Designate the engineering area with dangerous rock masses as the low-altitude remote sensing data collection area; ② Collecting terrain data of the project area: Using the UAV real-time differential positioning method (RTK) to collect basic terrain information data of the project area; ③ Plan UAV routes: Based on the basic terrain information data of the project area, plan UAV routes to ensure that the heading overlap of UAVs reaches 95% and the lateral overlap reaches 85%; ④ Carry out UAV close-up oblique photography: Use UAV close-up oblique photography to obtain close-up photogrammetric data of the project area; Step 2) Constructing a high-precision 3D real-scene model: Processing the close-up photogrammetry data of the project area obtained in step 1) to obtain a high-precision digital orthophoto and a digital elevation model, and constructing a high-precision 3D real-scene model; Step 3) Extracting the spatial coordinates of the outer boundary feature points of the dangerous rock body: Based on the high-precision three-dimensional real-scene model constructed in step 2), extract the spatial coordinates of the six outer boundary feature points of the dangerous rock body: ① Extract the spatial coordinates of the four outer boundary feature points on the surface of the dangerous rock mass, where the spatial coordinates of boundary feature point 1 are marked as (x1, y1, z1), the spatial coordinates of boundary feature point 2 are marked as (x2, y2, z2), the spatial coordinates of boundary feature point 3 are marked as (x3, y3, z3), and the spatial coordinates of boundary feature point 4 are marked as (x4, y4, z4); ② Extract the spatial coordinates of two feature points adjacent to the parent rock at the bottom of the dangerous rock mass: the spatial coordinates of boundary feature point 5 are marked as (x5, y5, z5), and the spatial coordinates of boundary feature point 6 are marked as (x6, y6, z6); Step 4) Calculate the spatial coordinates of the boundary feature points inside the dangerous rock body: Based on the spatial coordinates of the boundary feature points outside the dangerous rock body extracted in step 3), calculate the spatial coordinates of the boundary feature points inside the dangerous rock body: Select two characteristic points where the bottom of the dangerous rock mass meets the parent rock as the inner boundary characteristic points of the dangerous rock mass. The spatial coordinates of the inner boundary characteristic point 7 are marked as (x7, y7, z7), and the spatial coordinates of the inner boundary characteristic point 8 are marked as (x8, y8, z8); Calculate the spatial coordinates of the inner boundary feature points according to formula (1): (x7, y7, z7)=(x6, y6, z6)-(x2, y2, z2)+(x3, y3, z3) (x8, y8, z8)=(x5, y5, z5)-(x1, y1, z1)+(x4, y4, z4) (1) 5) Obtaining the volume parameters of the dangerous rock mass: Based on the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps 3) and 4), a spatial geometric model of the dangerous rock mass is established, and the volume parameters of the dangerous rock mass are calculated: The six outer boundary feature points and two inner boundary feature points on the surface of the dangerous rock mass form an irregular space hexahedron that can completely envelop the dangerous rock mass. The volume of the irregular space hexahedron is calculated to obtain the volume parameters of the dangerous rock mass.

2. The method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing according to claim 1, characterized in that: The volume of the irregular space hexahedron is used to calculate the volume parameters of the dangerous rock mass as follows: The irregular spatial hexahedron is divided into five tetrahedrons. According to the spatial coordinates of the boundary feature points of the dangerous rock mass obtained in steps S3 and S4, the volume of each tetrahedron is calculated, and the volume of the spatial hexahedron is obtained by cumulative summation: wherein the volume of the tetrahedron is calculated using formulas (2) to (6): In formulas (2) to (6), V i (i=1,2,3,4,5) are the volumes of the five tetrahedrons after segmentation, (x j ,y j , z j )(j=1, 2, 3, 4, 5, 6) are the spatial coordinates of the characteristic points of the tetrahedron to be determined. After obtaining the volumes of the five tetrahedrons, the volume of the spatial hexahedron is obtained by cumulative summation, as shown in formula (7): Where V is the volume of the space hexahedron; Calculate the volume of the irregular space hexahedron and obtain the volume parameters of the dangerous rock mass.

3. The method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing according to claim 1, characterized in that: The specific method of step 2) processing the close-up photogrammetry data of the project area obtained in step 1) to obtain a high-precision digital orthophoto and a digital elevation model, and constructing a high-precision three-dimensional real scene model comprises the following steps: ① Create digital orthophotos: Based on the photogrammetric data of the project area obtained in step 1), geometric correction is performed on the images using internal and external orientation elements and image control points to generate high-precision digital orthophotos. ② Create a digital elevation model (DEM): Based on the digital aerial triangulation method, the coordinates of the image points measured on the photos and the coordinates of a small number of field control points are solved indoors to obtain the plane and elevation coordinates of the infill points. This provides absolute directional control points for mapping in areas lacking field control points. Based on the obtained 3D coordinates of the infill points, spatial interpolation processing is performed to obtain a high-precision DE for the project area. ③ Create a 3D real-life model: Divide the high-precision digital orthophotos and high-precision DEM of the project area created in the above steps into multiple regional blocks. Send the digital orthophotos of one regional block and the high-precision DEM of the project area to the oblique photogrammetry system. Overlay the digital orthophotos on the DEM surface to generate a high-precision 3D real-life model of one regional block. Process them sequentially to obtain high-precision 3D real-life models of each regional block, and then perform splicing and integration processing to obtain a high-precision 3D real-life model of the project area.

4. The method for obtaining volume parameters of dangerous rock masses based on low-altitude remote sensing according to claim 1, characterized in that: If the bottom of the dangerous rock mass is not exposed, the spatial coordinates of boundary feature points 5 and 6 can be calculated by the distance between the surface of the dangerous rock mass and the parent rock, including the following steps: ① Measure the distance h between the surface of the dangerous rock mass and the parent rock: Rotate the 3D real scene model to the side of the dangerous rock mass, explore the structural surface between the dangerous rock mass and the parent rock, and measure the distance from the surface of the dangerous rock mass to the structural surface, which is the distance h between the surface of the dangerous rock mass and the parent rock; ② Calculate the coordinates of boundary feature points 5 and 6; feature point 5 can be generalized as the projection point of feature point 3 on the parent rock, with coordinates marked as (x5, y5, z5), and the value is equivalent to (x3-h, y3, z3); ​​feature point 6 can be generalized as the projection point of feature point 4 on the parent rock, with coordinates marked as (x6, y6, z6), and the value is equivalent to (x6-h, y6, z6).

Images