A method for extracting overhead contact height and pull-out value of tunnels during operation based on point cloud data

Abstract

The present invention discloses a method for extracting the height and pull-out value of the contact network of a tunnel during operation based on point cloud data, and belongs to the technical field of tunnel engineering measurement. The present invention discloses a method for extracting the height and pull-out value of a tunnel based on point cloud data. The method extracts the central axis of the tunnel by an improved two-way projection method, and extracts the cross section of the tunnel by using the direction of the central axis of the tunnel. Based on the relative position relationship of the cross-section point cloud, the point cloud data of the track and the contact network are initially and roughly extracted, and then according to the point cloud features, the three characteristic points of the track and the contact network are accurately extracted by setting a certain threshold, and finally the height and pull-out value of a certain section of the tunnel are obtained by the triangular geometric relationship. The advantages of the present invention are that the extraction of the tunnel section using three-dimensional laser point cloud data is efficient, accurate and intelligent, and the height and pull-out value of the corresponding section can be obtained, which greatly improves the measurement efficiency and accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel engineering measurement, and in particular relates to a method for extracting the overhead contact network height (usually referred to as "conductor height") and pull-out value of a tunnel during operation based on point cloud data. Background Art

[0002] Subway tunnels need maintenance and inspection during operation. The overhead contact height (usually referred to as "conductor height") is the vertical distance from the lower edge of the contact wire to the track plane. The height of the overhead contact wire is mainly measured at the contact wire positioning point, each hanging string point and the lowest point of the contact wire. If the overhead contact wire is too high, the pantograph will be offline and arc will burn the contact wire and pantograph. If it is too low, it will endanger the safety of personnel and oversized goods. In addition, when the overhead contact height (i.e., the conductor slope) changes too much within a small distance, it is easy to produce arcs, affecting the current collection quality of the pantograph and increasing the wear of the conductor of the slide. The contact wire pull-out value is the distance between the contact wire and the pantograph centerline at the specified position. In the straight section, the pantograph centerline coincides with the line centerline during the train's travel. The pull-out value is the distance between the vertical projection of the pantograph contact point and the line centerline. In the curved section, due to the height difference between the outer rail and the inner rail of the line, the train pantograph tilts to the inside of the curve with the body, and there is a certain distance difference between the pantograph centerline and the line centerline. The contact point between the pantograph and the catenary moves with the movement of the train position, and the pull-out value changes continuously, so as to achieve the purpose of uniform wear of the pantograph slide. If the pull-out value is too large, it will cause accidents such as pantograph scraping and wire breakage.

[0003] Traditional subway tunnel structural health inspections mostly use a combination of total stations, steel rulers, triangles and other measuring instruments and manual operations. The measurement workload during tunnel construction, completion acceptance and operation is large, and the traditional measurement method has high labor intensity. The observation accuracy is affected by the observation conditions and the quality of the operators. In addition, the monitored sections are discrete points, the number of measured sections is limited, and the accuracy is greatly affected by light, etc. Therefore, a high-precision, high-efficiency and intelligent measurement method is needed. 3D laser scanning technology 3D laser scanners are non-contact measurement, which can obtain massive point cloud data of the scanned tunnel with high density and high resolution. There is no requirement for light conditions, and the data inside the tunnel can be collected quickly, completely and comprehensively at one time. Through post-processing, the height and pull-out values ​​of any mileage of the operating tunnel can be obtained.

[0004] At present, many scholars have conducted extensive research on the application of 3D laser scanning in tunnels, but they mainly focus on the deformation of tunnels during tunnel construction and operation and the extraction of stagger between lining rings. There are few studies on the guide height and pull-out values ​​during tunnel operation, and no detailed and systematic extraction method has been proposed. This paper proposes a method for extracting guide height and pull-out values ​​suitable for tunnel operation: a method for extracting guide height and pull-out values ​​based on the section corresponding to each ring is proposed to guide the health detection of tunnels during operation. Summary of the invention

[0005] The present invention aims to provide a simple, fast and accurate method for extracting the height guide and pull-out values ​​during the operation period of a tunnel, so as to guide the maintenance during the operation period of the tunnel.

[0006] In order to achieve the above object, the present invention proposes a method for extracting tunnel height and pull-out values ​​during operation based on point cloud data, the method comprising the following steps:

[0007] Step 1: Point cloud data acquisition

[0008] Use a stationary 3D laser scanner to conduct on-site scanning to obtain tunnel point cloud data;

[0009] Step 2: Extract the central axis of the tunnel

[0010] After the overall point cloud data of the tunnel is in the absolute coordinate system, the spatial curve expressing the posture and trend of the tunnel, that is, the boundary line of the tunnel, is extracted, the tunnel point cloud data is projected onto the XOY plane to obtain the boundary point cloud, the plane equation of the boundary point cloud is fitted using the least squares method, the tunnel point cloud data is projected onto the YOZ plane, the upper boundary point is extracted, and a quadratic curve is fitted using the RANSAC random sampling consistency algorithm combined with the least squares method. This quadratic curve is projected onto the plane fitted by the XOY plane to obtain the spatial three-dimensional central axis of the tunnel, and the angle between the tunnel direction and the coordinate axis is obtained through the central axis;

[0011] Step 3: Extraction of tunnel sections during operation

[0012] After the overall point cloud data of the tunnel is in the absolute coordinate system, in order to extract the sections of different mileages and different numbers of rings, the bidirectional projection method is used to obtain the direction of the tunnel central axis, and the angle between the central axis at the mileage of the section to be extracted and the XOY plane and the YOZ plane are extracted. The point cloud data of the tunnel in the operation period is rotated so that its generatrix is ​​parallel to a certain coordinate axis of the coordinate system, and then the section is intercepted by reasonably setting the distance from the section point to the plane;

[0013] Step 4: Extraction of tunnel height and pull-out values

[0014] Project the cross-sectional point cloud data obtained in the third step onto a two-dimensional plane, translate the point cloud center to the center of the coordinate axis, determine the track point cloud position and the contact network point cloud position according to the coordinate range, and then determine the coordinates of the center points of the two tracks and the bottom point of the conductor. Determine the conductor height and pull-out value based on the coordinates of the center points of the two tracks and the bottom point of the conductor.

[0015] Beneficial Effects

[0016] The present invention aims to provide a simple, fast and accurate method for extracting the height guide and pull-out values ​​during the operation period of a tunnel, which is used to guide the tunnel construction and completion acceptance as well as the maintenance during the operation period.

[0017] 1) Applicability of the method. For the existing tunnel line, the angle between the tunnel point cloud and a certain coordinate axis is obtained by using the bidirectional projection method, and then rotated. The distance from point to surface is used for cross-section extraction, and the height guide value and pull-out value are calculated and analyzed. Combined with a certain subway line in Beijing, the applicability of this method for tunnels in operation is verified.

[0018] 2) Advantages of the method. 3D laser scanning technology is a high-precision, high-efficiency, and intelligent measurement method. Through post-processing, the cross-section of any mileage of the tunnel, as well as the height and pull-out values, can be quickly and accurately obtained. Compared with other methods, this method is relatively simple, fast, convenient, makes full use of massive point cloud raw data, has no requirements for computer configuration, and is highly accurate and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : Technology roadmap;

[0020] Figure 2 : Tunnel centerline extraction process diagram;

[0021] (a) Selection of point clouds near a ring

[0022] (b) Bidirectional projection onto the xoy plane and xoz plane

[0023] (c) Xoz graphics after extracting boundary points

[0024] (d) Fit the upper boundary point to a straight line

[0025] (e) Extracted central axis

[0026] (f) Extract the boundary points and perform plane fitting on the three-dimensional point graph

[0027] Figure 3 : Tunnel rotation process diagram;

[0028] (a) Projection image before rotation (b) Projection image after rotation

[0029] Figure 4 : Schematic diagram of tunnel cross section;

[0030] (a) Extracted cross-section (b) Projected cross-section

[0031] Figure 5 : Extract track point cloud range

[0032] (a)(b) Track point cloud range map (c) Height guide point cloud range map

[0033] Figure 6 : Extract orbit center coordinates

[0034] (a) Extraction of track point cloud within a certain thickness range

[0035] Figure 7 : Schematic diagram of the extracted high points and pull-out values;

[0036] (a) Find the high-derivative graph (b) Find the pull-out value graph

[0037] Figure 8 : Schematic diagram of conduction height and pull-out value;

[0038] Fig. 9 : Schematic diagram of the curve segment pull-out value; DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of technicians in the same industry, Beijing Metro Line 14 is taken as an example and the features and processes of the present invention are further described in detail with reference to the accompanying drawings, but the present invention is not limited to the following embodiments.

[0040] Step 1: Point cloud data acquisition

[0041] In order to obtain more accurate point cloud data, it is necessary to reasonably select the station spacing and scanning resolution.

[0042] After the station spacing and scanning resolution are determined, on-site scanning is carried out; while scanning, the positions of the scanner and the target are measured using a total station to determine the absolute coordinates of the station and the target.

[0043] Each time the point cloud data acquired by the 3D laser scanner is obtained, an independent internal coordinate system is established based on the center of the instrument to obtain the point cloud coordinate information. For multi-site cloud data, only through precise conversion between the coordinate systems can the unified point cloud coordinate information of the entire tunnel be obtained. Tunnel point cloud splicing is generally based on target splicing. Multiple targets are arranged in the overlapping area of ​​two adjacent stations, and it is ensured that more than three targets on non-straight lines are located in the overlapping area between the two stations. The coordinate system of the overall point cloud is completed through the conversion of common target point parameters. After the overall point cloud coordinate system is completed, the targets and measuring stations need to be assigned absolute coordinates measured by a high-precision total station so that the overall point cloud data is in an absolute coordinate system.

[0044] The main factors affecting the distance between measuring stations are the inner diameter of the tunnel and the maximum incident angle of the laser during scanning. The larger the incident angle of the 3D laser, the greater the error of the collected point cloud. max There is a fixed geometric relationship between the measuring station spacing S and the tunnel diameter D. The established geometric relationship is:

[0045]

[0046] In formula (1): θ max is the maximum incident angle within the scanning range, S is the distance between measuring stations, and D is the maximum width of the tunnel. It is verified by experiments that when the incident angle is greater than 60°, the error increases sharply. From formula (1), when θ max When =60°, S=1.7D.

[0047] The higher the resolution of the scanner, the denser the scanned point cloud, the higher the measurement accuracy, and the longer the scanning time. Therefore, we need to reasonably determine the resolution based on the time required for scanning resolutions of different levels and the requirements for point cloud data accuracy. After the station spacing and scanning resolution are determined, conduct on-site scanning to obtain tunnel point cloud data.

[0048] Step 2: Extract the central axis of the tunnel

[0049] Extraction of central axis by double projection method

[0050] The central axis of the tunnel is a spatial curve that represents the direction of the tunnel. The extracted tunnel section point cloud is perpendicular to the central axis of the tunnel at all times, so the accuracy of the central axis affects the subsequent processing of the tunnel point cloud data. This method extracts feature point clouds through the bidirectional projection method, and extracts the central axis of the curved tunnel based on the RANSAC algorithm combined with the least squares method.

[0051] The specific steps for extracting the central axis are:

[0052] 1) Assume that the 3D laser scanner is the coordinate origin, the Y axis is the tunnel direction, the X axis is perpendicular to the Y axis and both axes are located in the horizontal scanning plane, the Z axis is located in the vertical scanning plane, and the three axes are perpendicular to each other to form a right-handed coordinate system. First, project the tunnel point cloud data onto the XOY plane, such as Figure 2 (b) shows. Extract the boundary point set on both sides of the tunnel projection, as Figure 2 (f) as shown.

[0053] 2) Fit the plane according to the xyz coordinates of the extracted boundary points. Assume the equation of the plane is:

[0054] z=ax+by+c (2)

[0055] Randomly select 3 data points from the extracted boundary point cloud set. If the three points are not collinear, substitute the coordinates of the three points into the equation, solve the parameters a, b, and c, and obtain the plane model equation Z 1 Otherwise, three points are selected for calculation again. The error between the data point and the parameter model is represented by the distance from each point to the plane. The distance from each remaining point in the boundary point cloud to plane Z is calculated. 1 The distance d i Calculate the average distance d p , the standard deviation of the distance from the data point to the plane and the average distance is σ. Select the effective model with the smallest error, perform the least squares fitting plane on all the effective data points in the model, and finally obtain the plane equation of the parameters.

[0056] 3) Project the tunnel point cloud data onto the YOZ surface, such as Figure 2 (c) shows. The upper boundary point is extracted. A quadratic curve is fitted using the RANSAC random sampling consensus algorithm combined with the least squares method, as shown in the figure. As the expression of the two boundaries, that is:

[0057]

[0058] 4) Project the upper boundary of the YOZ plane calculated in 3) onto the plane fitted in 2) to obtain the three-dimensional central axis of the tunnel, as shown in Figure 2 (e) as shown.

[0059] Step 3: Extraction of tunnel sections

[0060] The specific steps for extracting cross sections are:

[0061] 1) Since the central axis information has been obtained, the normal vector direction information of the central axis for which the mileage needs to be calculated is extracted, and the original tunnel point cloud data is rotated and translated so that the generatrix of the tunnel point cloud data is parallel to the coordinate y axis. Figure 4 (a) as shown.i y i z i ] T and the changed coordinates [x' i y' i z' i ] T There is the conversion relationship in formula (3):

[0062]

[0063] 2) According to the tunnel design documents, the design coordinates (X, Y, Z) of the sections at different mileages (number of rings) can be obtained, and the plane normal vector and the design coordinates, the equation of the plane can be obtained as shown in formula (4).

[0064]

[0065] 3) The distance from the point cloud data of the tunnel surface after rotation and translation to the plane is used to intercept the tunnel cross section, such as Figure 4 As shown. Reasonably set the point-to-plane distance δ and set the cross-sectional thickness of the tunnel according to formula (5):

[0066] |yY|<δ (5)

[0067] Step 4: Extraction of height and pull-out values

[0068] 1. Extraction of straight line segment height and pull-out value

[0069] The specific steps to extract the lead height and pull-out values ​​are:

[0070] 1) The height of the contact wire (conductor height) is the vertical distance from the lower edge of the contact wire to the track plane, as shown in Figure 8. Extract the cross-sectional point cloud data corresponding to a certain ring in the mileage direction for analysis. First, analyze the center point of the extracted cross-sectional point cloud. Since the position information of the central axis has been extracted, the position coordinates of the center point of the cross section can be obtained, and then the center of the cross-sectional point cloud is translated to the center of the coordinate axis. In the subway tunnel during operation, the approximate range of the track point cloud and the contact network point cloud can be determined. According to this approximate coordinate range, the track point cloud and the contact network point cloud are initially extracted, such as Figure 5 shown.

[0071] 2) Extract the center position of the track top from the roughly extracted point cloud of one side of the track. The method is to extract the maximum value of the Z coordinate axis direction in the track part point cloud, set a threshold d, extract the point cloud within the range of the Z axis distance from the highest point threshold d, and calculate the average value of this part of the point cloud as the center point of the track top on one side, such as Figure 6As shown. Similarly, extract the center point of the top of the track on the other side. Extract the lowest point in the Z coordinate axis direction from the roughly extracted contact network point cloud range, set a threshold d, extract the point cloud within the range of the threshold d from the lowest point in the Z axis direction, and calculate the average value of this part of the point cloud as the lower boundary of the contact network conductor.

[0072] 3) By determining the coordinates of the center points of the two track tops and the coordinates of the lower boundary of the contact network through 2), the lead height and pull-out values ​​can be calculated, such as Figure 7 (a) shown.

[0073] like Figure 7 As shown in (b), the lengths of the three triangle sides are calculated based on the coordinates of the three feature points and formula (6):

[0074] l i =((z 1 -z 2) 2 +(x 1 -x 2 ) 2 )^ 1 / 2 (6)

[0075] After calculating the lengths of the three sides of the triangle, the Heron formula (7) can be used to calculate the area of ​​the triangle formed by the feature points.

[0076] S=(p*(pa)*(pb)*(pc))^ 1 / 2 (7)

[0077] Where p = (a + b + c) / 2;

[0078] According to the definition of the guide height, in this triangle, the height of this triangle is the guide height of this section. The guide height of this section is calculated using formula (8):

[0079] h=2S / a (8)

[0080] From the definition of the straight line segment pullout value, we know that the pullout value i is the distance between the vertex of the triangle and the center point of the base a. From the geometric relationship of the triangle, we can get the pullout value formula (9):

[0081] i=|(c^2-b^2) / (2*a)| (9)

[0082] Formulas (8) and (9) can be used to calculate the conductance and pull-out value of the operating tunnel in the straight area.

[0083] 2. Extract the curve segment value

[0084] Since the definition of pull-out value of straight section and curved section is different, the calculation of pull-out value of curved section is different from that of straight section. In the curved section, since the line center and the pantograph centerline do not coincide, the pull-out value is composed of two parts: the distance m between the contact line and the line center and the distance C between the line center and the pantograph centerline. For example, Figure 8 shown.

[0085] Like the straight line segment, the contact network and the point clouds of the tracks on both sides can be extracted, where the difference between the coordinates of the two tracks in the Y-axis direction is the superelevation △h, the difference between the center points of the two tracks and the contact network coordinates in the X-axis direction is m, and the conductor height can be approximately equal to H.

[0086] In the figure, △h is the superelevation; L is the center distance between the two track tops; H is approximately the guide height in practice, and according to the principle of similar triangles, the pull-out value S can be obtained as:

[0087] S=m+c=m+H△h / L (10)

[0088] The following is a cross-sectional point cloud data processing process for a specific number of rings in the operating tunnel of Dajing Station on Beijing Metro Line 14. The height diversion and pull-out values ​​of the tunnel section are extracted in the MATLAB program. MATLAB can output the height diversion h = 4.042612324001168m; the pull-out value i = 0.018605684808577m. It has been verified that the errors of the height diversion and pull-out values ​​extracted by this method are small.

[0089] In summary, the present invention aims to provide a method for quickly and accurately extracting the height guide and pull-out values ​​during the tunnel operation period, which is used to guide the operation safety and maintenance of subway tunnels.

Claims

1. A method for extracting the height and pull-out value of the tunnel contact network during operation based on point cloud data, characterized in that: The following steps are involved: Step 1: point cloud data acquisition; Use a stationary 3D laser scanner to conduct on-site scanning to obtain tunnel point cloud data; Step 2: Extract the central axis of the tunnel; After the overall point cloud data of the tunnel is in the absolute coordinate system, the spatial curve expressing the posture and trend of the tunnel, that is, the boundary line of the tunnel, is extracted, the tunnel point cloud data is projected onto the XOY plane to obtain the boundary point cloud, the plane equation of the boundary point cloud is fitted using the least squares method, the tunnel point cloud data is projected onto the YOZ plane, the upper boundary point is extracted, and a quadratic curve is fitted using the RANSAC random sampling consistency algorithm combined with the least squares method. This quadratic curve is projected onto the plane fitted by the XOY plane to obtain the spatial three-dimensional central axis of the tunnel, and the angle between the tunnel direction and the coordinate axis is obtained through the central axis; Step 3: Extraction of tunnel sections during operation; After the overall point cloud data of the tunnel is in the absolute coordinate system, in order to extract the sections of different mileages and different numbers of rings, the bidirectional projection method is used to obtain the direction of the tunnel central axis, and the angle between the central axis at the mileage of the section to be extracted and the XOY plane and the YOZ plane are extracted. The point cloud data of the tunnel in the operation period is rotated so that its generatrix is ​​parallel to a certain coordinate axis of the coordinate system, and then the section is intercepted by reasonably setting the distance from the section point to the plane; Step 4: Extraction of tunnel height conductance and pull-out value; Project the cross-sectional point cloud data obtained in the third step onto a two-dimensional plane, translate the point cloud center to the center of the coordinate axis, determine the track point cloud position and the contact network point cloud position according to the range of the coordinates, and then determine the coordinates of the center points of the two tracks and the bottom point of the conductor, and determine the conductor height and pull-out value according to the coordinates of the center points of the two tracks and the bottom point of the conductor; The third step is to extract the tunnel cross section, and the specific steps are: 1) Since the central axis information has been obtained, the normal vector direction information of the central axis for which the mileage needs to be calculated is extracted, and the original tunnel point cloud data is rotated and translated so that the generatrix of the tunnel point cloud data is parallel to the coordinate y axis; 2) According to the tunnel design documents, obtain the design coordinates (X, Y, Z) of different mileage or ring sections, and use the plane normal vector And the design coordinates can obtain the equation of the plane; 3) Using the distance from the point cloud data of the tunnel surface after rotation and translation to the plane to intercept the tunnel cross section; The fourth step is to extract the tunnel conductance and the pull-out value, and the specific steps are: 1) Extract the cross-sectional point cloud data corresponding to a certain ring in the mileage direction for analysis. First, analyze the center point of the extracted cross-sectional point cloud, determine the range of the track point cloud and the contact network point cloud, and roughly extract the track point cloud and the contact network point cloud. 2) Based on the position characteristics of the roughly extracted track point cloud and contact network point cloud, the track coordinate position and the contact network lower boundary position are accurately extracted using the threshold; 3) The definition of the pull-out value of the straight segment and the curved segment is different. Therefore, according to the different mileage information, the pull-out value of the curved segment and the straight segment is calculated separately, and the guide height and pull-out value of a certain section are calculated using the triangular geometric relationship.

2. A method for extracting tunnel height and pull-out values ​​during operation based on point cloud data according to claim 1, characterized in that: The specific steps of the second step include: 1) Assume that the 3D laser scanner is the coordinate origin, the Y axis is the direction of the tunnel, the X axis is perpendicular to the Y axis and both axes are located in the horizontal scanning plane, the Z axis is located in the vertical scanning plane, and the three axes are perpendicular to each other to form a right-handed coordinate system; project the tunnel point cloud data onto the XOY plane, and extract the boundary point sets on both sides of the tunnel projection; 2) Fit the plane according to the xyz coordinate values ​​of the extracted boundary points; assume the equation of the plane is: z=ax+by+c Randomly select 3 data points from the extracted boundary point cloud set. If the three points are not collinear, substitute the coordinates of the three points into the equation, solve the parameters a, b, c, and obtain the plane model equation Z1; otherwise, re-select three points for calculation, and the error between the data point and the parameter model is expressed by the distance from each point to the plane. Calculate the distance di from each remaining point in the boundary point cloud set to the plane Z1; calculate the average distance dp, and the standard deviation of the distance from the data point to the plane and the average distance is σ; select the effective model with the smallest error, perform the least squares method to fit the plane to all the effective data points in the model, and finally obtain the plane equation of the parameters; 3) Project the tunnel point cloud data onto the YOZ plane and extract the upper boundary point; use the RANSAC random sampling consensus algorithm combined with the least squares method to fit a quadratic curve; 4) Project the upper boundary of the YOZ plane calculated in step 3) onto the plane fitted in step 2) to obtain the three-dimensional central axis of the tunnel.

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