JP7586410B2 - Displacement measurement method and absolute coordinate assignment method - Google Patents

Description

The present invention relates to a displacement measuring method and an absolute coordinate providing method .

In the maintenance of mountain tunnels, visual inspection is performed from vehicles as a daily inspection, and close-up visual inspection and hammering inspection are performed as periodic inspections (every 5 years). If spalling, lifting, cracks, or other abnormalities of the lining concrete are found during periodic inspections, the displacement of the inner wall surface may be measured to observe the progress and identify the cause of the abnormality. Conventionally, relative displacement between two points was measured using a convergence measure or a laser displacement meter, and displacement of an arbitrary point was measured using a total station, but in recent years, 3D laser scanners (sometimes written as "LS") are sometimes used to measure the displacement of the inner wall surface of tunnels. A 3D laser scanner is a measuring instrument that can obtain highly accurate three-dimensional coordinates as a point cloud from a remote location in a short time. Specifically, it irradiates a large number of laser beams around it and receives the laser beams reflected by an object. This allows the shape of the surface of an object to be measured as a set of coordinates of points that cover the surface. This set of measured points is called "point cloud data," and the distance of the object can be calculated using dedicated software. Point cloud data is in relative coordinates (local coordinates), and when converting relative coordinates to absolute coordinates (global coordinates), a target is used as a landmark. The target is set up in advance before scanning with a 3D laser scanner, and the absolute coordinates of the target are obtained in some way.
In this regard, for example, a technology described in Patent Document 1 has been developed. In the technology described in Patent Document 1, a target whose tunnel coordinates (global coordinates) are known is installed on the wall of a tunnel, and the inside of the tunnel is scanned with a 3D laser scanner to obtain the scan coordinates (local coordinates) of the target. Then, based on the scan coordinates of the target and the tunnel coordinates, the scan coordinates of the tunnel cross section are converted to the tunnel coordinates. The target is, for example, a body that serves as a sign surface attached to an outer frame so as to be freely rotatable around a rotation axis, and is fixed to the wall by anchor bolts.

JP 2014-089211 A

For example, when using a paper target as a target for LS, a method of acquiring the absolute coordinates of the center position of the target can be to measure the center position of the target using a total station (sometimes written as "TS"). Specifically, it is assumed that the TS instrument position is identified using the backsight method (angle and distance measurement from a known point) with the total station, and the coordinates of the center position of the paper target are acquired using the non-prism target function. However, the distance measurement accuracy with a non-prism target is about "3 mm", and it is thought that the accuracy may be even worse in the dark environment inside a tunnel.
In addition, products with a TS prism built into the center of a spherical target (reference sphere) and products with a TS prism fixed by a bolt or the like at a known distance from a spherical target (reference sphere) are on the market. By using these products, it is possible to accurately obtain the absolute coordinates of the center of the target, but the reference sphere itself is expensive because it needs to be a highly accurate true sphere, and in addition, manufacturing technology is required to accurately attach the prism, etc., which further increases the product price. Therefore, when measuring the wall displacement of a long section of a linear structure such as a tunnel, using these products is problematic in terms of cost. In other words, one method of synthesizing point cloud data is to use a target, and in this case, the target is also used to synthesize the point cloud data. For example, if it is not possible to measure the entire shape of the object in one scanning, the position of the 3D laser scanner is changed and the object is partially scanned multiple times, and then the partially measured point cloud data is connected using dedicated software. For example, three targets are used in one scanning as a basis for the synthesis. In order to measure the amount of displacement on the inner wall of a tunnel, it is necessary to change the position of the 3D laser scanner and perform measurements repeatedly, so it is time-consuming to move the target to the evaluation point each time a measurement is performed, and it is not realistic in terms of cost to install expensive targets at all evaluation points. Therefore, it is desirable to use targets that are as inexpensive as possible.
From this viewpoint, the present invention provides a displacement measuring method and an absolute coordinate assigning method that are economical and capable of assigning absolute coordinates to point cloud data with high accuracy.

The displacement measuring method according to the present invention is a displacement measuring method for measuring the displacement of a lining concrete inside a tunnel over time using a 3D laser scanner. This displacement measuring method has first to fourth steps.
In the first step, the absolute coordinates of a reference point provided on the wall of the tunnel are measured by a surveying instrument. In the second step, a sheet-like first target is placed on the reference point. In the third step, the wall is scanned by the 3D laser scanner to obtain point cloud data of the wall, and absolute coordinates are assigned to the point cloud data based on the position of the first target in the point cloud data and the absolute coordinates of the reference point. In the fourth step, after a predetermined period of time has elapsed since the third step, the wall is scanned again to obtain new point cloud data of the wall, and the displacement is calculated by comparing the new point cloud data with the point cloud data obtained earlier. A hole for positioning is formed in the first target, and in the second step, the hole is aligned with the reference point.
In the second step, sheet-like second targets are further arranged in the tunnel axial direction without overlapping the reference points. In the third step, the wall surface is repeatedly scanned while the position of the 3D laser scanner is moved in the tunnel axial direction to obtain a plurality of point cloud data of a predetermined section divided in the tunnel axial direction, and the point cloud data is synthesized using the first target or the second target included in each point cloud data, and absolute coordinates are reflected. The second target does not have a hole for alignment that the first target has.
The displacement measurement method according to the present invention is economical because it can use inexpensive paper targets as targets . It also ensures the same level of accuracy as the "sphere + prism product" and can perform highly accurate measurements inside tunnels. It is also economical because it can use inexpensive paper targets even for long measurement sections.

The absolute coordinate assigning method according to the present invention is a method for associating absolute coordinates with point cloud data measured by a 3D laser scanner. This absolute coordinate assigning method has first to third steps.
In the first step, the absolute coordinates of a reference point provided on the measurement target are measured by a surveying instrument. In the second step, a sheet-like first target is placed on the reference point. In the third step, the measurement target is scanned by the 3D laser scanner to obtain point cloud data of the measurement target, and absolute coordinates are assigned to the point cloud data based on the position of the first target in the point cloud data and the absolute coordinates of the reference point. A hole for positioning is formed in the first target, and in the second step, the hole is aligned with the reference point.
In the second step, sheet-like second targets are arranged in a predetermined direction without overlapping the reference points, and further placed. In the third step, the position of the 3D laser scanner is moved in a predetermined direction while repeatedly scanning the measurement target to obtain a plurality of point cloud data for a predetermined section divided in the predetermined direction, and the point cloud data is synthesized using the first target or the second target included in each point cloud data, and absolute coordinates are reflected. The second target does not have a hole for alignment that the first target has.
The absolute coordinate assignment method according to the present invention is economical because it is possible to use inexpensive paper targets as targets. Furthermore, even if inexpensive paper targets are used, absolute coordinates can be assigned to point cloud data with high accuracy .

The present invention makes it possible to assign absolute coordinates to point cloud data economically and with high accuracy.

1 is a schematic configuration diagram of a displacement measurement system using a displacement measurement method according to an embodiment of the present invention. 1A and 1B are an example of a paper target for LS (paper target), in which FIG. 1A is an overall view of the paper target, and FIG. 1B is an enlarged view of a main portion of the paper target. FIG. 13 is a diagram for explaining a method of installing an LS target. 1 is an example of a flowchart illustrating a displacement measurement method according to an embodiment of the present invention. 1 is an image diagram for explaining a displacement measuring method according to an embodiment of the present invention. 1 is an image diagram for explaining a displacement measuring method according to an embodiment of the present invention. 1 is an image diagram for explaining a displacement measuring method according to an embodiment of the present invention. 1 is an image diagram for explaining a displacement measuring method according to an embodiment of the present invention.

Below, the form for carrying out the present invention will be described in detail with reference to the drawings as appropriate. Each figure is merely a schematic illustration to allow a sufficient understanding of the present invention. Therefore, the present invention is not limited to the illustrated examples. In each figure, common or similar components are given the same reference numerals, and duplicate explanations thereof will be omitted.

<Displacement Measuring System According to the Embodiment>
A displacement measurement system 1 using a displacement measurement method according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic configuration diagram of the displacement measurement system 1.
The displacement measurement system 1 is a system that measures displacement (deformation of the tunnel wall surface) inside a tunnel. The displacement measurement system 1 can be used for various types of tunnels and purposes without being limited to the type or purpose of the tunnel. In this embodiment, an example of an application will be described, taking as an example an inspection for maintenance after a tunnel is completed.
As shown in FIG. 1, the displacement measurement system 1 includes a total station 2 as a surveying instrument, a 3D laser scanner 3, a management device 4, a TS target 5, and an LS target 6. The total station 2, the 3D laser scanner 3, the TS target 5, and the LS target 6 are arranged inside a tunnel, and the location of the management device 4 is not particularly limited. The total station 2 and the 3D laser scanner 3 are capable of data communication with the management device 4. The management device 4 may be a component that forms part of a cloud system. The total station 2 and the 3D laser scanner 3 may be configured as one measuring device. In other words, the displacement measurement system 1 can be realized using a measuring device having the functions of a total station and a 3D laser scanner.

The total station 2 shown in FIG. 1 is a type of surveying instrument, and has a function as a theodolite that measures horizontal and vertical angles, and a function as a range finder that measures distances using light or radio waves. In other words, the total station 2 measures the distance to the sighting point, the horizontal angle of the sighting direction relative to the reference line, and the angle of the sighting direction relative to the horizontal plane (hereinafter collectively referred to as "position"). The total station 2 measures the distance and angle of a reference point (e.g., "rating point") provided on the wall of a tunnel, for example, and calculates the absolute coordinates of the reference point from the measured distance and angle. When the center point of the TS target 5 is placed on the reference point provided on the wall, the reference point and the center point are in the same position, so there are cases where the reference point and the center point are not distinguished from each other in the description. Note that the reference point on the wall may be directly surveyed by a surveying instrument without using the TS target 5. The total station 2 transmits to the management device 4 at least one of the position (distance, angle) of the center point of the TS target 5 (i.e., the reference point provided on the wall of the tunnel) and the absolute coordinates calculated from it.
The TS target 5 is attached to the object of surveying by the total station 2 and used. The TS target 5 is installed, for example, at a reference point (rating point) provided on the wall of a tunnel. The TS target 5 is, for example, a designated mark made up of a combination of a circle and a crosshair, marked on a rectangular (including a square) sheet. The intersection of the crosshairs of the designated mark is the center point of the designated mark. The TS target 5 is preferably a reflective sheet that reflects light, and is preferably an adhesive-type reflective sheet with an adhesive applied to the back side so that it can be attached to the inner wall of a tunnel. The TS target 5 does not necessarily have to be rectangular, and may be of other shapes (for example, a polygon other than a square, or a circle).

The 3D laser scanner 3 is a type of measuring device, and obtains highly accurate three-dimensional coordinates as a point cloud from a remote location in a short time. Specifically, it irradiates a large number of laser beams around the object and receives the laser beams reflected by the object. This allows the shape of the surface of the object to be measured as a set of coordinates of points that cover the surface (point cloud data). The point cloud data is a relative coordinate (local coordinate with the installation position of the 3D laser scanner 3 as the origin), and when converting the relative coordinates to absolute coordinates (global coordinates), the LS target 6 is used as a landmark. The LS target 6 can also be used to synthesize point cloud data. The 3D laser scanner 3 may be equipped with an imaging unit (e.g., a camera) in addition to the scanner unit. The image captured by the imaging unit is used, for example, to observe the LS target 6. Details will be described later. The 3D laser scanner 3 transmits the obtained point cloud data (including the relative coordinates) and the captured image to the management device 4.
The LS targets 6 are used as markers (references) when processing point cloud data acquired by the 3D laser scanner 3. In this embodiment, some of the LS targets 6 are installed so as to overlap the TS targets 5 (i.e., reference points provided on the wall surface of the tunnel). A method for installing the LS targets 6 will be described later. The LS targets 6 are in the form of a sheet, and for example, a designated mark is printed on the surface. A paper target made of paper is known as the cheapest LS target, and it is economical to use this paper target as the LS target 6.

An example of a paper LS target 6 (paper target) is shown in Fig. 2. Fig. 2(a) is an overall view of the LS target 6, and Fig. 2(b) is an enlarged view of region X of the LS target 6. The LS target 6 shown in Fig. 2 is a white paper of a predetermined size (e.g., A4 size) printed in black and laminated with an anti-reflection coating.
The LS target 6 has a designation mark 61 and identification information 62 attached below the designation mark 61. The identification information 62 identifies the LS target 6 and is composed of, for example, numbers or letters.
The designation mark 61 serves as a marker in the processing of point cloud data, and the designation mark 61 in this embodiment is a pair of black triangular figures 61a, 61a arranged opposite each other (an hourglass pattern). The figures 61a, 61a are isosceles triangles, and are the same size. As shown in FIG. 2B, a positioning hole 61c is formed in the center of the designation mark 61. The hole 61c has a circular shape, and the center of the hole 61c coincides with the center of the designation mark 61. The hole 61c may be a hole that allows the designation mark (particularly the center point) of the TS target 5 arranged on the back side to be visually recognized (for example, a small hole made with a needle or the like may be used). By making the size of the hole 61c as small as possible within the range where the designation mark on the back side can be visually recognized, errors in the coordinate processing described below are reduced.
A method of installing the LS target 6 on the wall surface of a tunnel will be described with reference to Fig. 3. Fig. 3 is a diagram for explaining the method of installing the LS target 6.
As shown in Fig. 3, the designated mark on the TS target 5 is viewed through the hole 61c of the LS target 6, the LS target 6 is positioned so that the center point of the designated mark on the TS target 5 coincides with the center point of the hole 61c, and the LS target 6 is attached to the wall of the tunnel so as to overlap the TS target 5. This causes the positions (absolute coordinates) of the reference point (e.g., rating point) set on the wall of the tunnel, the center point of the designated mark on the TS target 5, and the center point of the designated mark on the LS target 6 to coincide. Incidentally, by matching the center point of the hole 61c with the center point of the designated mark on the TS target 5 (i.e., the reference point set on the wall of the tunnel), errors in the coordinate processing described below are reduced.

The management device 4 shown in Fig. 1 is a device that manages the displacement measurement system 1 and has a function of processing point cloud data. The management device 4 is, for example, a personal computer. The management device 4 acquires at least one of the position (distance, angle) of the center point of the TS target 5 (i.e., a reference point provided on the wall surface of the tunnel) and absolute coordinates calculated therefrom from the total station 2. The management device 4 also acquires point cloud data (including relative coordinates) and captured images from the 3D laser scanner 3.
The management device 4 has, for example, coordinate processing software and point cloud processing software. The coordinate processing software realizes a process of converting the relative coordinates of the point cloud data into absolute coordinates. The point cloud processing software realizes a process of merging (combining) the point cloud data acquired by the 3D laser scanner 3 and excluding unnecessary points. For example, the management device 4 realizes a coordinate processing function (sometimes called a "coordinate processing unit") by executing the coordinate processing software by a CPU (Central Processing Unit). In addition, the management device 4 realizes a point cloud processing function (sometimes called a "point cloud processing unit") by executing the point cloud processing software by a CPU. Note that the coordinate processing method and the point cloud data processing method described here are merely examples, and other methods may be used.

The coordinate processing unit of the management device 4 identifies the LS target 6 from, for example, an image captured by the 3D laser scanner 3 or measured point cloud data, and assigns the absolute coordinates of the center point (reference point) obtained by measuring the TS target 5 to the relative coordinates corresponding to the LS target 6. The method of identifying the LS target 6 is not particularly limited, and various methods can be used.
For example, the coordinate processing unit determines the position of the LS target 6 by an image recognition technique using an image captured by an imaging unit (e.g., a camera). In this case, the shape of the LS target 6 and the designation mark 61 printed on the LS target 6 correspond to the image recognition technique (e.g., a specific design or color pattern). The coordinate conversion unit specifies the position of the LS target 6 in the point cloud data from the correspondence between the position of the LS target 6 specified by the image recognition technique and the point cloud data.
The coordinate processing unit also determines the position of the LS target 6 by a pattern recognition technique using the shape of the surrounding area acquired by the scanner unit. In this case, the shape of the LS target 6 and the designated mark printed on the LS target 6 correspond to the pattern recognition technique (for example, a specific design or pattern is realized by a color or surface treatment that does not reflect laser light). Note that an observer may visually observe the LS target 6 from the point cloud data. In this case, the shape of the LS target 6 and the designated mark printed on the LS target 6 are distinguishable by visual inspection from the point cloud data (for example, a specific design or pattern is realized by a color or surface treatment that does not reflect laser light).

When the point cloud data is measured multiple times, the point cloud processing unit of the management device 4 identifies the LS targets 6 from, for example, images captured by the 3D laser scanner 3 or the measured point cloud data, and synthesizes (combines) the multiple point cloud data using the identified LS targets 6 as landmarks (references). The method of identifying the LS targets 6 is not particularly limited, and for example, the LS targets 6 are identified by a method similar to that of the coordinate processing unit. It is necessary to use multiple LS targets 6 to synthesize the point cloud data, and although it depends on the presence or absence of a tilt correction function of the 3D laser scanner 3, for example, three LS targets 6 are used.

<Displacement measuring method according to the embodiment>
A displacement measurement method according to an embodiment will be described with reference to Fig. 4 and Fig. 5D (and Fig. 1 to Fig. 3 as appropriate). Fig. 4 is an example of a flowchart showing the displacement measurement method. Figs. 5A to 5D are conceptual diagrams for explaining the displacement measurement method.
As shown in Fig. 4, first, the observer attaches the TS targets 5 to the wall inside the tunnel (S101). For example, the TS targets 5 are attached in at least three places. Fig. 5A shows the state in which the TS targets 5 are attached to the wall of the tunnel. Note that the TS targets 5 may be attached without setting a reference point, in which case the center point of the designated mark on the TS target 5 becomes the reference point. Then, the observer uses the total station 2 to survey the positions of the three TS targets 5 (center points of the designated marks) (S102).

Next, the observer makes a hole in the center of the paper target for the 3D laser scanner to create the LS target 6 shown in Fig. 2 (S103). Next, the observer looks into the TS target 5 through the made hole 61c, aligns the hole 61c with the center point of the TS target 5, and attaches the LS target 6 onto the TS target 5 (S104). The state in which the LS target 6 is attached onto the TS target 5 is shown in Fig. 5B.
The observer also attaches paper targets for the 3D laser scanner to the wall surface in the tunnel axial direction within the measurement section (S105). The paper targets attached in S105 do not have holes and are referred to as "non-hole targets 7". The LS targets 6 and non-hole targets 7 do not have to be arranged in a straight line, and may be arranged offset in the vertical direction. The LS targets 6 and non-hole targets 7 should be arranged at a certain interval. However, in order to ensure the measurement accuracy of the 3D laser scanner 3, the incidence angle of the laser on the wall surface needs to be, for example, "within 45°" (if the angle is shallow, the distance measurement accuracy is significantly deteriorated), so it is necessary to comprehensively judge the relationship between the target position and the incidence angle. At the beginning and end of the measurement section, it is preferable to install the LS targets 6 superimposed on the TS targets 5 that have been surveyed. The state in which the non-hole targets 7 are attached to the wall surface of the tunnel is shown in FIG. 5C.

Next, the observer uses the 3D laser scanner 3 to measure (scan) the shape data of the tunnel wall surface and obtain point cloud data of the wall surface (S106). Specifically, while moving the 3D laser scanner 3 in the tunnel axial direction, the observer repeatedly scans the wall surface to obtain multiple point cloud data of a predetermined section divided in the tunnel axial direction. The state of measurement using the 3D laser scanner 3 is shown in FIG. 5D.
For example, first, the 3D laser scanner 3 is installed at position T1 and scans the wall surface to obtain point cloud data within the range of region R1. At this time, since the LS target 6 included in region R1 is overlapped with the TS target 5, absolute coordinates can be assigned to the point cloud data within the range of region R1. Next, the 3D laser scanner 3 is installed at position T2 and scans the wall surface to obtain point cloud data within the range of region R2. Here, a total of six paper targets (three LS targets 6 and three holeless targets 7) are included in the region R2 to be measured. Since the LS target 6 included in region R2 is overlapped with the TS target 5, absolute coordinates can be assigned to the point cloud data within the range of region R2. Next, the 3D laser scanner 3 is installed at position T3 and scans the wall surface to obtain point cloud data within the range of region R3. Here, a total of six paper targets (six holeless targets 7) are included in the region R3 to be measured. In this manner, measurements are repeated.

The management device 4 synthesizes all the measured point cloud data, and for point cloud data including only paper targets (i.e., the holeless target 7) that do not overlap the TS target 5, reflects the absolute coordinates of the point cloud data acquired before or after (S107). For example, absolute coordinates can be assigned to the point cloud data in the range of region R3 by reflecting the point cloud data in the range of region R2. In this way, absolute coordinates can be assigned to the point cloud data obtained by scanning only the holeless target 7. It is preferable to correct the absolute coordinates by matching them with the absolute coordinates assigned to the LS target 6 installed at the end of the measurement section.
In this way, the measurement of the displacement of the reference tunnel wall surface is completed. After a predetermined period of time has elapsed, the observer performs steps S106 and S107 again to obtain new point cloud data. The observer then calculates the displacement of the wall surface by comparing the newly obtained point cloud data with the point cloud data obtained earlier (for example, the reference point cloud data). Note that steps S101 to S106 are an example of an absolute coordinate assignment method. The absolute coordinate assignment method can be realized by using the TS target 5 and the LS target 6, and can be applied to any purpose other than tunnels.

As described above, the displacement measurement method and absolute coordinate assignment method according to the embodiment are economical because an inexpensive paper target can be used as the LS target 6. In addition, the same accuracy as the "sphere + prism product" can be ensured, and absolute coordinates can be assigned to the point cloud data with high accuracy, so that highly accurate measurements can be performed inside the tunnel. In addition, the method is economical because an inexpensive paper target can be used even for long measurement sections. The material cost of the LS target 6 is, for example, about several hundred yen, and measurements can be achieved inexpensively even if multiple sheets are attached to the tunnel wall at once.
Although the embodiment of the present invention has been described above, the present invention is not limited to this, and can be practiced within the scope of the claims.

1 Displacement measurement system 2 Total station (surveying instrument)
3 3D laser scanner 4 Management device 5 TS target 6 LS target (first target, target)
61 Designation mark 61c Hole 7 Target without hole (second target)

Claims (2)

A displacement measurement method for measuring the displacement of a tunnel lining concrete over time using a 3D laser scanner,
A first step is to measure the absolute coordinates of a reference point on the wall of the tunnel using a surveying instrument;
A second step of placing a sheet-shaped first target on the reference point;
A third step of acquiring point cloud data of the wall surface by scanning the wall surface with the 3D laser scanner, and assigning absolute coordinates to the point cloud data based on the position of the first target and the absolute coordinates of the reference point in the point cloud data;
and a fourth step of scanning the wall surface again after a predetermined period of time has elapsed since the third step, acquiring new point cloud data of the wall surface, and calculating a displacement by comparing the new point cloud data with the point cloud data acquired earlier.
The first target has a hole for alignment formed therein, and in the second step, the hole is aligned with the reference point ;
In the second step, a sheet-shaped second target is further placed in a line in the tunnel axial direction without overlapping with the reference point,
In the third step, the position of the 3D laser scanner is moved in the tunnel axial direction while repeatedly scanning the wall surface to obtain a plurality of point cloud data of a predetermined section divided in the tunnel axial direction, and the point cloud data is synthesized using the first target or the second target contained in each point cloud data, and absolute coordinates are reflected;
The second target does not have an alignment hole formed therein, which is the same as the first target.
A displacement measuring method comprising: An absolute coordinate assignment method for associating absolute coordinates with point cloud data measured by a 3D laser scanner, comprising:
A first step of measuring absolute coordinates of a reference point provided on a measurement target using a surveying instrument;
A second step of placing a sheet-shaped first target on the reference point;
and a third step of acquiring point cloud data of the measurement object by scanning the measurement object with the 3D laser scanner, and assigning absolute coordinates to the point cloud data based on the position of the first target and the absolute coordinates of the reference point in the point cloud data,
The first target has a hole for alignment formed therein, and in the second step, the hole is aligned with the reference point ;
In the second step, a sheet-like second target is further placed in a predetermined direction without being overlapped with the reference point,
In the third step, the position of the 3D laser scanner is moved in a predetermined direction while repeatedly scanning the measurement target to obtain a plurality of point cloud data of a predetermined section divided in a predetermined direction, and the point cloud data is synthesized using the first target or the second target included in each point cloud data, and absolute coordinates are reflected;
The second target does not have an alignment hole formed therein, which is the same as the first target.
Absolute coordinate assignment method.

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