Small-opening underground cavity volume detection method and device

Abstract

The invention discloses a small-opening underground cavity volume detection method and device, and the method comprises the steps: detecting an underground cavity, transmitting the underground cavity to a laser radar for point cloud data collection, carrying out the average grouping of a part of obtained point cloud data, calculating the cavity volume, solving an average volume A and a standard deviation B, and if B / A is greater than or equal to a set precision threshold value, determining that the underground cavity is a small-opening underground cavity; if not, the number of the point cloud data in each group of point cloud data is increased for recalculation, the optimal data scale in each group of point cloud data is finally obtained, the vertical position of the laser radar in the cavity is adjusted, and the newly obtained point cloud data is grouped according to the optimal data scale to calculate the cavity volume; the steps are repeated until the average volume A obtained through solving is larger than the average volume A obtained through solving in the last time, the position with the maximum cavity volume obtained through calculation is the position of a cavity opening, and the maximum cavity volume serves as the final cavity volume; and generating the internal form of the whole cavity by using any group of point cloud data in one part of point cloud data at the position with the maximum volume of the cavity.

Description

Technical Field

[0001] The present invention belongs to the technical field of road detection, especially for airport roads, and particularly relates to a method and device for detecting the volume of small underground cavities. Background Art

[0002] Areas such as airport runways and aprons are subjected to huge aircraft takeoff and landing loads, ground traffic loads, and the influence of natural environmental factors. At the same time, the interaction of various factors such as the laying of underground pipelines, the flow of groundwater, and the natural settlement of soil may cause changes in the soil structure under the airport, and thus form cavities. Current conventional detection methods include visual inspection, radar method, acoustic wave method, infrared detection method, laser scanning method, etc. These techniques can obtain the location of the cavity underground, but the accuracy of acquisition needs to be improved; at the same time, in addition to detecting the location of the cavity, rectifying these cavities also requires measuring the shape and volume of the cavity.

[0003] As the current mainstream method, ground penetrating radar technology is a very effective non-destructive detection means. Its main devices include a radar and an antenna, and the detection method is: moving the ground penetrating radar equipment along a predetermined path, emitting and receiving radar waves, and analyzing the location where the cavity is located based on the collected data. However, it has obvious defects, mainly manifested in:

[0004] (1) Although ground penetrating radar can collect the location of the cavity, it cannot collect the shape and volume of the cavity.

[0005] (2) For small-sized cavities, the radar waves may not be able to generate sufficient reflection signals to detect potential cavities, and misjudgment may occur during judgment.

[0006] (3) The cost of ground penetrating radar equipment and data processing software is relatively high, especially in cases where high precision and high resolution are required. Summary of the Invention

[0007] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method and device for detecting the volume of small underground cavities, so as to solve the problem that the prior art can only detect the location of the cavity and cannot obtain the internal data of the cavity, and reduce the equipment cost and data processing cost.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A method for detecting the volume of small underground cavities includes the following steps:

[0010] S1, detecting the underground cavity and sending a lidar from the position at the top of the cavity;

[0011] S2, turn on the laser radar to collect point cloud data, and the point cloud data collected within the effective collection time of the laser radar is recorded as one point cloud data;

[0012] S3, grouping the point cloud data into average groups, calculating the cavity volumes for several groups of point cloud data, and solving the average volume A and standard deviation B;

[0013] S4, if B / A is greater than or equal to the set accuracy threshold, then increase the number of point cloud data in each group of point cloud data, recalculate the average volume A and standard deviation B until B / A is less than the set accuracy threshold. At this time, the number of point cloud data in each group of point cloud data is the optimal data scale, and the average volume obtained by each group of point cloud data is the cavity volume corresponding to the point cloud data;

[0014] S5, adjusting the vertical position of the laser radar in the cavity, repeating S2, and grouping a portion of the point cloud data according to the data scale, and calculating the cavity volume;

[0015] S6, repeat S5 until the average volume A obtained by solution is greater than the last solution, the position with the largest calculated cavity volume is the position of the cavity opening, and the largest cavity volume is taken as the final cavity volume;

[0016] S7, using any set of point cloud data in a point cloud data set when the cavity volume is at the maximum position in S6, to generate the internal shape of the entire cavity.

[0017] In one embodiment, S1 uses geological radar to detect underground cavities, predicts the top position of the cavity, drills a hole at the predicted top position of the cavity, and sends a laser radar into the cavity.

[0018] In one embodiment, the laser radar is an ultra-wide-angle 4D laser radar with a field of view extended to 360° horizontally and 90° vertically, thereby realizing three-dimensional space point cloud acquisition with a hemispherical field of view.

[0019] In one embodiment, S3, packages the point cloud data to obtain multiple point cloud data groups, uses a convex hull algorithm to solve the first N point cloud data groups to obtain N cavity volumes, and solves the average volume A and standard deviation B of the N cavity volumes.

[0020] In one embodiment, in S3, each group of point cloud data has 2000 point cloud data, and in S4, 2000 point cloud data are added each time, and the accuracy threshold is set to 5%.

[0021] In one embodiment, volume comparison is performed using radars at different positions to ensure that the radar is at the mouth of the cavity, thereby ensuring that the laser point cloud can feedback the entire internal boundary of the cavity and measure the accurate cavity volume.

[0022] In one embodiment, the measured point cloud is used to display the point cloud in a three-dimensional coordinate system through drawing software to display the cavity outline.

[0023] Another aspect of the present invention further provides a small-mouth underground cavity volume detection device for implementing the small-mouth underground cavity volume detection method, the detection device comprising a ground support device, a protection tube, a telescopic device and a laser radar;

[0024] The top of the telescopic device is connected to the ground supporting device, and the laser radar is installed at the bottom. The inner diameter of the protective tube is larger than the telescopic device, and is used to be pre-buried and penetrate the top of the cavity after detecting the underground cavity. The telescopic device carries the laser radar through the protective tube and explores the cavity.

[0025] In one embodiment, the ground support device is a tripod, and the telescopic device is an electric push rod equipped with a wireless controller, which is connected below the tripod.

[0026] In one embodiment, the telescopic device is connected to the ground support device through a precise control device. The precise control device is a movable rod, including an external fixing ring welded to the inner side of the ground support device. A swing arm, a gear and an internal screw are installed in the external fixing ring. The internal screw is connected to the top of the telescopic device, and the swing arm is connected to the gear, which is meshed with the internal screw. The gear is driven to rotate by shaking the swing arm, and then the internal screw is driven to achieve precise displacement control.

[0027] Compared with the prior art, the present invention can not only detect the position of the cavity, but also use lidar scanning to obtain the internal data of the cavity, and then calculate the volume of the cavity based on these data and generate a three-dimensional data graph, thereby obtaining accurate data such as its shape and volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the detection method of the present invention.

[0029] Figure 2 It is a schematic diagram of the structure of the detection device of the present invention.

[0030] Figure 3 This is a schematic diagram of the change of B / A and true error with the number of point clouds. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0032] refer to Figure 1 As shown, the present invention provides a method for detecting the volume of a small underground cavity, comprising the following steps:

[0033] S1. Detect the underground cavity and send a lidar into the cavity from the top position of the cavity.

[0034] After detecting a possible cavity using a ground penetrating radar (GPR) or other geological radar, predict the top position of the cavity, drill a hole at the predicted top position of the cavity, and use a lifting device to send the lidar into the cavity. Further, in this step, as Figure 2 shown, the device can achieve sending the lidar into the cavity. The device mainly includes a ground support device 1, a protection tube 2, and a telescopic device 4. When combined with the lidar sent in, it constitutes the main component of the small-mouth underground cavity volume detection device of the present invention.

[0035] In the figure, the ground support device 1 is a tripod for ground support. The top of the telescopic device 4 is connected to the ground support device 1. Specifically, the top can be connected directly below the vertex of the tripod and is in a vertical state, and the lidar is installed at its bottom. The inner diameter of the protection tube 2 is larger than that of the telescopic device 4. After detecting the underground cavity, the protection tube 2 is pre-buried so that the protection tube 2 penetrates the top of the cavity and extends into the cavity. The length of the protection tube 2 should not be too long and only needs to extend into the top of the cavity. The protection tube 2 is the access path for the telescopic device 4. The telescopic device 4 carries the lidar through the protection tube 2 and extends into the cavity.

[0036] In an embodiment of the present invention, the telescopic device 4 can be an electric push rod equipped with a wireless controller to quickly control the lifting of the lidar for preliminary adjustment. At the same time, the ground support device 1 and the telescopic device 4 can be connected through a precise control device 3 for precise adjustment. For example, the precise control device 3 is a movable rod that can be manually controlled. It mainly includes a swing arm, a gear, an internal screw, and an external fixed ring. Among them, the swing arm, the gear, and the internal screw are all installed inside the external fixed ring. The internal screw is connected to the top of the telescopic device 4. The precise control device 3 is welded to the inner side of the ground support device 1 through the external fixed ring. The swing arm is connected to the gear, and the gear meshes with the internal screw. By shaking the swing arm, the gear rotates, thereby driving the internal screw to achieve precise control of the displacement. Through the precise control device 3, a small range of lifting of the telescopic device 4 is achieved, thereby precisely adjusting the position of the radar.

[0037] In an embodiment of the present invention, the protection tube 2 can be a PVC tube. After drilling the channel, it is first extended into the cavity to provide a channel for the lidar to extend into.

[0038] Before sending the lidar into a possible cavity, first drill a hole on the ground and then dig down to near the entrance of the possible cavity shown by the ground penetrating radar. Then, pre-bury the protection tube 2 along the pre-drilled hole. After pre-burying, connect the ground support device 1 and the telescopic device 4, and send the lidar into the cavity along the protection tube 2. This can play a certain protective role for the lidar.

[0039] S2. Turn on the lidar to collect point cloud data.

[0040] Based on the ground drilling operation situation, predict the height from the ground to the top of the cavity. Insert the lidar to the predicted height through operation S1 and start the lidar to collect the point cloud data inside the cavity. In the present invention, the lidar uses an ultra-wide-angle 4D lidar (Unitree 4D LiDar), which has ultra-wide-angle scanning ability. The field of view (FOV) is extended to 360° horizontally and 90° vertically, enabling the acquisition of three-dimensional space point clouds with a hemispherical field of view.

[0041] Record the point cloud data collected within the effective acquisition time of the lidar as a set of point cloud data. In this embodiment, the effective acquisition time is set to be more than 20S.

[0042] Furthermore, about 20,000 data are collected per second. More than 400,000 point cloud data can be collected in more than 20S. The point cloud data collected within the effective acquisition time is recorded as a set of point cloud data.

[0043] S3. Divide a set of point cloud data into average groups. For several groups of point cloud data among them, calculate the cavity volume respectively, and solve the average volume A and the standard deviation B.

[0044] In this embodiment, a set of point cloud data is sub-packaged to obtain multiple groups of point cloud data. By default, 2,000 point cloud data are taken as a group, and then the computer is used to solve 10 cavity volumes based on the first 10 groups of point cloud data.

[0045] Furthermore, in this step, the convex hull algorithm is used to solve the volume according to each group of data. Based on the 10 cavity volumes obtained from the first 10 groups of point cloud data, calculate the average volume A of these 10 cavity volumes and the standard deviation B of these 10 cavity volumes.

[0046] S4. Determine the data group scale.

[0047] When S3 is completed, check the ratio of the standard deviation B to the average volume A of the volume calculation results of different groups of 2,000-point cloud data. When the ratio is less than the set precision threshold, for example, 5%, it is considered that the precision is acceptable. Otherwise, it is considered that the precision is insufficient, and the number of point cloud data in each group of point cloud data needs to be increased. Repeat S3 to calculate the average volume A and the standard deviation B of each group after increasing the point cloud number. In this embodiment, the number of point cloud data is increased by 2,000 each time. Until the ratio of the standard deviation B to the average volume A is less than the set precision threshold, which is 5% in this embodiment, the number of point cloud data in each group of point cloud data is the optimal data scale at this time, and the average volume obtained from each group of point cloud data is the accurate cavity volume corresponding to this set of point cloud data.

[0048] Taking a cuboid cavity with dimensions: 0.53×0.46×0.35 as an example, the lidar operates for 20S and obtains 432,000 point cloud data. This 432,000 point cloud data is regarded as one portion. The data of this portion is grouped according to the acquisition time. With 2,000 point cloud data as one group, a total of 216 groups are divided. Similarly, when taking 4,000, 6,000, 8,000, 10,000, and 20,000 point cloud data as one group, they are divided into 108, 72, 54, 43, and 21 groups respectively. Select the first 10 groups, and the calculated volume average value, variance and other results are shown in Table 1. Among them, B / A and the true error are plotted in Figure 3 .

[0049] Table 1

[0050] Point cloud quantity Standard deviation B Volume average value A Standard volume B / A True error 2000 0.0322 0.0653 0.08533 49.31087 23.47357 4000 0.0159 0.0714 0.08533 22.26891 16.32486 6000 0.0102 0.0803 0.08533 12.70237 5.894762 8000 0.00628 0.0832 0.08533 7.548077 2.496191 10000 0.00341 0.0848 0.08533 4.021226 0.621118 20000 0.00281 0.0845 0.08533 3.325444 0.972694

[0051] From Table 1 and Figure 3 , it can be seen that for the cavity with a true volume of 0.0853m 3 , when the number of data in each group of point cloud data is 2,000, 4,000, 6,000, and 8,000, B / A is greater than 5%. Therefore, it can be determined that the calculated results have relatively large errors. Therefore, continue to increase the number of point cloud data in a single group. When the number is 10,000, B / A = 4.02%, which is less than 5%. At this time, the error is relatively small. The number of 10,000 can be used as the number of point cloud data in each group. To verify the rationality, continue to increase the number of point cloud data in a single group to 20,000. B / A = 3.33% is also less than 5%, but the calculation duration and the cloud map output time of 20,000 point cloud data are much longer than those of 10,000. Therefore, for the 0.0853m 3 cavity, 10,000 is the optimal number of point clouds. Comparing the true errors of 10,000 and 20,000 point cloud data, it is found that both are less than 1%. Therefore, both have sufficient accuracy.

[0052] S5, Volume comparison.

[0053] To ensure that the predicted position is at the top of the cavity, after completing the test and calculation of one group of point cloud data, the vertical elevation of the lidar can be finely adjusted through the movable rod, repeat S2, and group a portion of point cloud data according to the data scale determined by S4, and calculate the cavity volume.

[0054] S6, Repeat S5 for multiple groups of experiments until the average volume A obtained by solving is greater than the previous solution. The position with the largest calculated cavity volume is the position of the lidar, that is, the position of the cavity opening, and the largest cavity volume is used as the final cavity volume; that is, when the lidar is basically at the position of the cavity opening, the measured volume is the most accurate. This step ensures that the radar is at the cavity opening by comparing the volumes calculated using radars at different positions, so as to ensure that the laser point cloud can feedback the internal boundary of the entire cavity and measure the accurate cavity volume.

[0055] S7. Calculate the volume display form. After completing S6, use any set of point cloud data in the point cloud data at the position with the largest cavity volume to generate a cavity form for visual inspection. For example, use the measured point cloud data and, through drawing software, display the point cloud in a three-dimensional coordinate system to show the cavity contour.

[0056] Through the above solution, the present invention can achieve high-precision and automated underground cavity detection, greatly improving the accuracy and efficiency of detection. At the same time, visual interactive control can be realized, and the form and volume of small underground cavities can be accurately, quickly, and simply detected, providing accurate cavity position information, which helps with rapid positioning and repair.

Claims

1. A method for detecting the volume of a small underground cavity, characterized in that: The steps include: S1, detects underground cavities and feeds the LiDAR from the top of the cavity; S2, turn on the laser radar to collect point cloud data, and the point cloud data collected within the effective collection time of the laser radar is recorded as one point cloud data; S3, grouping the point cloud data into average groups, calculating the cavity volumes for several groups of point cloud data, and solving the average volume A and standard deviation B; S4, if B / A is greater than or equal to the set accuracy threshold, then increase the number of point cloud data in each group of point cloud data, recalculate the average volume A and standard deviation B until B / A is less than the set accuracy threshold. At this time, the number of point cloud data in each group of point cloud data is the optimal data scale, and the average volume obtained by each group of point cloud data is the cavity volume corresponding to the point cloud data; S5, adjusting the vertical position of the laser radar in the cavity, repeating S2, and grouping a portion of the point cloud data according to the data scale, and calculating the cavity volume; S6, repeat S5 until the average volume A obtained by solution is greater than the last solution, the position with the largest calculated cavity volume is the position of the cavity opening, and the largest cavity volume is taken as the final cavity volume; S7, using any set of point cloud data in a point cloud data set when the cavity volume is at the maximum position in S6, to generate the internal shape of the entire cavity.

2. The method for detecting the volume of a small underground cavity according to claim 1, characterized in that: The S1 uses a geological radar to detect the underground cavity, predict the top position of the cavity, drill a hole at the predicted top position of the cavity, and send the laser radar into the cavity.

3. The method for detecting the volume of a small underground cavity according to claim 1, characterized in that: The laser radar is an ultra-wide-angle 4D laser radar with a field of view extended to 360° horizontally and 90° vertically, realizing the acquisition of three-dimensional space point cloud with a hemispherical field of view.

4. The method for detecting the volume of a small underground cavity according to claim 1, characterized in that: The S3 is to package the point cloud data into multiple point cloud data groups, use the convex hull algorithm to solve the first N point cloud data groups to obtain N cavity volumes, and solve the average volume A and standard deviation B of the N cavity volumes.

5. The method for detecting the volume of a small underground cavity according to claim 1, characterized in that: In S3, each set of point cloud data contains 2000 point cloud data, and in S4, 2000 point cloud data are added each time, and the accuracy threshold is set to 5%.

6. The method for detecting the volume of a small underground cavity according to claim 1, characterized in that: The volume comparison is calculated using radars at different positions to ensure that the radar is at the mouth of the cavity, thereby ensuring that the laser point cloud can feedback the entire internal boundary of the cavity and measure the accurate cavity volume.

7. The method for detecting the volume of a small underground cavity according to claim 1, characterized in that: Using the measured point cloud, the point cloud is displayed in a three-dimensional coordinate system through drawing software to show the cavity outline.

8. A small underground cavity volume detection device, characterized in that: Used to implement the small underground cavity volume detection method as described in any one of claims 1 to 7, comprising a ground support device (1), a protection pipe (2), a telescopic device (4) and a laser radar; The top of the telescopic device (4) is connected to the ground support device (1), and the laser radar is installed at the bottom. The inner diameter of the protective tube (2) is larger than that of the telescopic device (4), and is used to be pre-buried and penetrate the top of the cavity after detecting the underground cavity. The telescopic device (4) carries the laser radar through the protective tube (2) and probes into the cavity.

9. The small-mouth underground cavity volume detection device according to claim 8, characterized in that: The ground support device (1) is a tripod, and the telescopic device (4) is an electric push rod equipped with a wireless controller, which is connected below the tripod.

10. The device for detecting the volume of a small underground cavity according to claim 8, characterized in that: The telescopic device (4) is connected to the ground support device (1) via a precise control device (3). The precise control device (3) is a movable rod, comprising an external fixing ring welded to the inner side of the ground support device (1). A swing arm, a gear and an internal screw are installed inside the external fixing ring. The internal screw is connected to the top of the telescopic device (4). The swing arm is connected to the gear, which meshes with the internal screw. The gear is driven to rotate by shaking the swing arm, thereby driving the internal screw to achieve precise displacement control.

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