CN107588913A - A kind of deflection of bridge span detecting system and detection method - Google Patents

Abstract

The invention discloses a kind of deflection of bridge span detecting system and detection method, including multiple targets, image collecting device, laser ranging module, amount of deflection computing module and operating unit, wherein, image collecting device and amount of deflection computing module are connected with operating unit；Image collecting device and laser ranging module are connected with amount of deflection computing module.The measurements of multiple tested point deflection values on Longspan Bridge is realized by horizontally rotating for image collecting device and laser ranging module；The problems such as solving prior art needs multiple CCD cameras or laser range finder, and precision is not high, and cost is higher, operation inconvenience, and practicality is not strong.

Description

A bridge deflection detection system and detection method

technical field

The invention relates to the technical field of bridge monitoring, in particular to a bridge deflection detection system and detection method.

Background technique

The deflection of the bridge refers to the magnitude of the longitudinal line displacement of the centroid at a certain cross section of the beam body in the direction perpendicular to the axis. Once the deflection of the bridge exceeds the allowable range, or it cannot return to its original position after being subjected to external forces, it can be judged that the bridge has potential safety hazards. Therefore, the detection of bridge deflection is an important task to evaluate the operation status of the bridge according to its structural characteristics and bearing capacity during the static load test.

Traditional bridge deflection detection methods usually use dial gauges, displacement meters and other instruments for contact measurement. When the bridge crosses rivers, roads, railways, and canyons, contact instruments will face the problem of being unable to install due to the inability to lay out supports.

In recent years, non-contact methods for bridge deflection measurement using laser technology and digital image technology have emerged. However, when measuring the deflection of long-span bridges, these two methods need to deploy multiple laser rangefinders or CCD cameras along the bridge, which will bring problems such as difficult instrument layout, complicated operation, easily restricted site, and high cost.

Contents of the invention

In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a bridge deflection detection system and method, which solves the problem that multiple CCD cameras or laser range finders need to be used in the prior art, and the deflection measurement accuracy is not high. , high cost, inconvenient operation, and poor practicability.

In order to achieve the above object, the present invention adopts the following technical solutions:

A bridge deflection detection system comprising a plurality of targets, an image acquisition device, a laser distance measuring module, a deflection calculation module and an operation unit, wherein the image acquisition device and the deflection calculation module are connected to the operation unit; the image acquisition device and the laser distance measurement The modules are all connected with the deflection calculation module;

A target is set at each point of the bridge to be tested;

The image acquisition device is used to acquire the initial image of the target when the bridge to be tested is not loaded and the target image of the target when the bridge to be tested is loaded;

The laser ranging module is used to measure the distance between the image acquisition device and the target;

The initial image, the target image and the distance between the image acquisition device and the target are all input into the deflection calculation module, and the deflection value at the point to be measured is calculated;

The deflection value is transmitted to the operation unit by the deflection calculation module, and the operation unit displays the calculated deflection value;

The image acquisition device transmits the acquired real-time images to the operation unit, and the operation unit is used to control the image acquisition device so that the image acquisition device can acquire images of the target.

Specifically, the image acquisition device includes a telescope optical system, an area array CCD camera and a cloud platform, the telescope optical system is installed above the cloud platform, and the area array CCD camera is installed behind the telescope optical system through a bracket.

Specifically, the operation unit includes an image display module, a deflection display module, a pan-tilt control module, and a pan-tilt position recording module.

A method for bridge deflection detection using the bridge deflection detection system, comprising the following steps:

Step 1: Set up a calibration plate on one side of the bridge to be tested, calibrate the bridge deflection detection system, and obtain the distance L between the front end of the telescope optical system and the calibration plate and the displacement value represented by the unit pixel. The functional relationship f(L);

Step 2, the area array CCD camera obtains the real-time image of the bridge to be measured, and transmits to the display in the image display module; adjust the tripod below the cloud platform, adjust the vertical position of the cloud platform, and utilize the cloud platform control module to adjust the cloud platform. The horizontal position of the stage, so that the image of the target at the point to be measured is displayed in the image display module;

Step 3, using the laser ranging module to obtain the distance L _target between the front end of the telescope optical system and the target (1), and sending it to the deflection calculation module;

Step 4, using an area array CCD camera to collect the initial image P of the target (1) when the bridge is not under load, and deliver it to the deflection calculation module;

Step 5, apply a load to the bridge, use the area array CCD camera to collect the target image Q of the target when the bridge is under load, and send it to the deflection calculation module;

Step 6, the deflection calculation module uses the distance L _target between the front end of the telescope optical system and the target, the initial image P, the target image Q and the functional relationship f(L), to calculate the deflection of the bridge to be measured where the target is located;

Step 7, the deflection value obtained in step 6 is displayed on the deflection display module, and the pan-tilt position recording module records the horizontal position of the pan-tilt at this moment;

Step 8: Control the horizontal rotation of the pan-tilt through the pan-tilt control module, and repeat steps 2 to 7 for targets set on other points of the bridge to be measured, so as to detect the deflection of all points to be measured.

Specifically, in said step one, the bridge deflection detection system is calibrated to obtain the functional relationship f(L) between the distance L between the front end of the telescope optical system and the calibration plate and the displacement value represented by the unit pixel, specifically including The following steps:

Use the area array CCD camera in the image acquisition device to shoot the calibration plate, and use the laser ranging module to obtain the distance L between the front end of the telescope optical system and the calibration plate; according to the number of pixels contained in the unit distance in the calibration plate image , obtain the displacement value represented by the unit pixel at the distance L; change the distance between the front end of the telescope optical system and the calibration plate several times, and obtain the displacement value represented by the unit pixel at different distances L;

Taking the distance L as the abscissa and the displacement value represented by the unit pixel as the ordinate, the functional relationship f(L) between the distance L and the displacement value represented by the unit pixel is obtained by fitting.

Specifically, the formula used to obtain the distance L between the front end of the telescope optical system and the calibration plate by using the laser ranging module is as follows:

θ = θ ₁ + θ ₂

L2=(a+L1)×cosθ

L=L2-b

Among them, a is the distance between the front end of the laser ranging module and its center point; b is the distance between the front end of the telescope optical system and its center point; L1 is the distance between the front end and the calibration plate measured by the laser ranging module; L2 is the distance between the center point of the telescope optical system and the calibration plate; θ ₁ is the angle between the laser ranging module and the horizontal direction; θ ₂ is the angle between the telescope optical system and the horizontal direction; θ is the laser ranging module The angle between the axis and the axis of the telescope optical system.

Specifically, in the step 3, the distance L _target between the front end of the telescope optical system and the target is obtained by using the laser ranging module, and the formula adopted is as follows:

θ = θ ₁ + θ ₂

L2=(a+L1)×cosθ

L _target = L2-b

Among them, a is the distance between the front end of the laser ranging module and its center point; b is the distance between the front end of the telescope optical system and its center point; L1 is the distance between the front end and the target measured by the laser ranging module; L2 is the distance between the center point of the telescope optical system and the target; θ ₁ is the angle between the laser ranging module and the horizontal direction; θ ₂ is the angle between the telescope optical system and the horizontal direction; θ is the axial direction of the laser ranging module Angle with the axis of the telescope optical system.

Specifically, the deflection calculation module in the step 6 uses the distance L _target between the front end of the telescope optical system and the target, the initial image P, the target image Q and the functional relationship f(L) to calculate the bridge where the target is located. The deflection of the measuring point includes the following steps:

Set up an m×n target surface coordinate system on the collected images in units of pixels;

Obtain the vertical coordinates of the centers of the four solid circles on the initial image P as y ₁ , y ₂ , y ₃ , and y ₄ respectively, and calculate the vertical coordinate y of the target center position when the bridge is not under load:

Obtain the y-coordinates of the centers of the four solid circles on the target image Q as y ₁ ', y ₂ ', y ₃ ', and y ₄ ' respectively, and calculate the y-coordinate of the target center position when the bridge is under load, as follows:

Calculate the number of pixels of the vertical offset of the target center position in the target surface coordinate system:

Δy=y'-y

Find the f (L) value when the distance between the front end of the telescope optical system and the target is the L _target ;

Use the following formula to calculate the deflection projection value Y _{α of the deflection value at the target on the projection plane α} :

Y _α =f(L)×Δy

Then the deflection value Y at the target:

Y _＝ Yα/ _cosθ2

Among them, _θ2 is the angle between the telescope optical system and the horizontal direction.

Compared with the prior art, the present invention has the following technical effects:

1. The bridge deflection detection system of the present invention can realize non-contact measurement, and can overcome the problem that contact measuring instruments cannot be installed when the bridge crosses rivers, highways, railways, and canyons; it can realize the automatic measurement of large-span bridge deflection, which is different from traditional Compared with the measurement method using dial indicator and displacement meter, and the existing measurement method using laser technology and digital image technology, only a small number of personnel are needed to complete the arrangement of the instrument and the measurement of the deflection, which is easy to operate and can save labor costs .

2. The bridge deflection detection method of the present invention can realize the re-measurement of the deflection value of the designated point to be measured.

Description of drawings

Fig. 1 is the connection block diagram of bridge deflection detection system of the present invention;

Fig. 2 is the structural representation of bridge deflection detection system of the present invention;

Fig. 3 is a schematic diagram of the distance calculation between the front end of the telescope optical system and the target projection plane α;

Fig. 4 is the curve diagram of the functional relationship f (L) between the distance L and the displacement value represented by the unit pixel; wherein, the horizontal axis represents the distance L, and the unit is m; the vertical axis represents the displacement value represented by the unit pixel, the unit is mm/pixel;

Each label in the figure represents: 1—target, 2—image acquisition device, 21—telescope optical system, 22—area CCD camera, 23—cloud platform, 3—laser ranging module.

The solution of the present invention will be further explained and described in detail in conjunction with the accompanying drawings and specific embodiments.

detailed description

According to the above-mentioned technical scheme, referring to Fig. 1, the bridge deflection detection system of the present invention includes a plurality of targets 1, an image acquisition device 2, a laser ranging module 3, a deflection calculation module and an operation unit, wherein the image acquisition device 2 and the deflection calculation The modules are all connected to the operation unit; the image acquisition device 2 and the laser ranging module 3 are both connected to the deflection calculation module.

Target 1 includes a white background plate on which four black solid circles are set. The bridge deflection detection system of the present invention is used to measure bridge deflection. During specific measurement, a plurality of points to be measured are set on the same side of the bridge to be measured, and one target 1 is set on each point to be measured, and four targets 1 are arranged. The central symmetrical position of the black solid circle coincides with the position of the point to be measured.

Referring to Fig. 2, image acquisition device 2 comprises telescopic optical system 21, area array CCD camera 22 and cloud platform 23, and wherein cloud platform 23 adopts ioptron CEM60, and the tripod of cloud platform 23 is placed on the bridge to be measured to set the side of target 1; The telescope optical system 21 is installed on the top of the cloud platform 23, and the area array CCD camera 22 is installed on the rear of the telescope optical system 21 by a bracket, and is arranged on the focal plane of the telescope optical system 21 reticle, so that the area array CCD camera 22 Imaging; said cloud platform 23 is provided with RS232 interface, and this interface is connected with operating unit, and cloud platform 23 carries GPS and can record its horizontal position, and position information is delivered to operating unit by RS232 interface, thereby realizes operating unit control Rotation and positioning of the cloud platform 23. Described area array CCD camera 22 is provided with video output interface, and this interface is also connected with operating unit, is used for the image that area array CCD camera 22 collects is transmitted in the operating unit, so that observe image in real time, find target position .

The distance between the telescope optical system 21 and the surface of the bridge should be greater than the shortest focusing distance of the telescope optical system 21 to ensure clear images can be displayed in the image display module.

The laser ranging module 3 is installed directly above the telescope optical system 21 and connected to the housing of the telescope optical system 21 through a bracket. The laser distance measuring module 3 is connected with the deflection calculation module through a data line, and is used to transmit the distance and angle information collected by the laser distance measurement module 3 to the deflection calculation module.

Described operation unit comprises image display module, deflection display module, cloud platform control module and cloud platform position recording module, and wherein image display module is connected with the video output interface of area array CCD camera 22, is used for displaying area array CCD camera 22 to collect image, so as to observe the image in real time and find the target position. Both the pan-tilt control module and the pan-tilt position recording module are connected to the RS232 interface of the pan-tilt 23, and are used to realize the operation unit to control the rotation and positioning of the pan-tilt 23. The deflection display module is used to display the measured deflection value.

The bridge deflection detection system of the present invention, its specific work process is as follows: a plurality of to-be-measured points of the bridge to be measured is respectively provided with a target 1, utilizes the image display module and the pan-tilt control module in the operation unit to find the position of the target 1, Utilize the pan-tilt position recording module in the operation unit to record the position of the pan-tilt 23, utilize the area array CCD camera 22 in the image acquisition device 2 to collect the initial image of the target 1 when the bridge is not under load and the target of the target 1 when the bridge is under load image, utilize the laser ranging module 3 to obtain the distance between the front end of the telescope optical system 21 and the target 1; the initial image, the target image and the distance between the front end of the telescope optical system 21 and the target 1 are all input into the deflection calculation module, and the deflection The calculation module outputs the deflection value of the point to be measured on the bridge where the target 1 is located, and uses the deflection display module of the operation unit to display it.

The method for bridge deflection measurement using the bridge deflection detection system described in the present invention comprises the following steps:

Step 1, the bridge deflection detection system of the present invention is calibrated, and the calibration method is as follows:

A calibration plate is set on one side of the point to be measured of the bridge to be measured, and the distance L between the front end of the telescope optical system 21 and the calibration plate is obtained by using the laser ranging module 3, and the area array CCD camera 22 in the image acquisition device 2 is used The calibration board is photographed, and the image acquisition device 2 transmits the collected calibration board image to the image display module in the operation unit for display;

According to the number of pixels included in the unit distance (mm) in the calibration plate image, obtain the displacement value represented by the unit pixel under the distance L; change the distance between the telescope optical system 21 front end and the calibration plate for many times, Obtain the displacement value represented by the unit pixel in the case of different distance L;

Referring to Fig. 4, with the distance L as the abscissa and the displacement value represented by the unit pixel as the ordinate, the functional relationship f(L) between the distance L and the displacement value represented by the unit pixel is obtained by a fitting method;

f(L)＝p ₁ *L ³ +p ₂ *L ² +p ₃ *L+p ₄

Among them, p ₁ =1.914e-06; p ₂ =-0.0003363; p ₃ =0.0208; p ₄ =-0.3781.

In this embodiment, the range of the distance L is (45m, 75m), and the range of the distance L should include the maximum distance between the telescope optical system 21 and the bridge surface.

Wherein, referring to FIG. 3 , α is the projection surface of the calibration plate actually observed by the telescope optical system, and the calculation method for the distance L between the front end of the telescope optical system 21 and the calibration plate is:

θ = θ ₁ + θ ₂

L2=(a+L1)×cosθ

L=L2-b

Among them, a is the distance between the front end of the laser ranging module and its center point; b is the distance between the front end of the telescope optical system and its center point; L1 is the distance between the front end and the calibration plate measured by the laser ranging module; L2 is the distance between the center point of the telescope optical system and the calibration plate; L is the distance between the front end of the telescope optical system and the calibration plate, that is, the distance between the front end of the telescope optical system and the projection surface α of the calibration plate; θ ₁ is the angle between the laser ranging module and the horizontal direction; θ ₂ is the angle between the telescope optical system and the horizontal direction; θ is the angle between the axis of the laser ranging module and the axis of the telescope optical system.

Step 2, the real-time image of the bridge to be measured obtained by the area array CCD camera 22 is displayed in the image display module in the operating unit, adjust the tripod below the cloud platform 23, adjust the vertical position of the platform 23, and use the platform control module Adjust the horizontal position of the cloud platform 23 so that a target 1 on the bridge to be measured appears in the field of view of the telescope optical system 21, that is, the target 1 is displayed in the image display module; in order to make the image in the image display module clearer, adjust the The coarse and fine quasi-focus spirals of the telescope optical system 21 are used for focusing.

Step 3, use the laser ranging module 3 to obtain the distance L _target between the front end of the telescope optical system 21 and the target 1, and send it to the deflection calculation module; the calculation formula of the L _target is as follows:

θ = θ ₁ + θ ₂

L2=(a+L1)×cosθ

L _target = L2-b

Among them, a is the distance between the front end of the laser ranging module and its center point; b is the distance between the front end of the telescope optical system and its center point; L1 is the distance between the front end and the target measured by the laser ranging module; L2 is the distance between the center point of the telescope optical system and the target; θ ₁ is the angle between the laser ranging module and the horizontal direction; θ ₂ is the angle between the telescope optical system and the horizontal direction; θ is the axial direction of the laser ranging module Angle with the axis of the telescope optical system.

Step 4, use the area array CCD camera 22 to collect the initial image P of the target 1 when the bridge is not under load, and send it to the deflection calculation module;

Step 5, apply a load to the bridge, use the area array CCD camera 22 to collect the target image Q of the target 1 when the bridge is under load, and send it to the deflection calculation module;

Step 6, the deflection calculation module uses the distance L _target between the front end of the telescope optical system 21 and the target 1, the initial image P, the target image Q and the functional relationship f(L), to calculate the bridge to be tested where the target 1 is located The deflection of a point is calculated as follows:

Set up an m×n target surface coordinate system on the collected images in units of pixels;

The improved Hough transform is used to identify the black solid circles on the initial image P, and the vertical coordinates of the centers of the four solid circles on the initial image P are y ₁ , y ₂ , y ₃ , y ₄ When the load is applied, the ordinate y of the center position of the target is:

Using the improved Hough transform to identify the black solid circle on the target image Q, the ordinates of the centers of the four solid circles on the target image Q are y ₁ ', y ₂ ', y ₃ ', y ₄ ' respectively, It is calculated that when the bridge is under load, the ordinate y' of the target center position is:

Calculate the number of pixels of the vertical offset of the target center position in the target surface coordinate system:

Δy=y'-y

Find the f (L) value when the distance between the front end of the telescope optical system 21 and the target 1 is the L _target ;

Use the following formula to calculate the deflection projection value Y _{α of the deflection value at the target on the projection plane α} :

Y _α =f(L)×Δy

Then the deflection value Y at the target:

Y _＝ Yα/ _cosθ2

Wherein, θ ₂ is the angle between the telescope optical system 21 and the horizontal direction.

In step seven, the deflection value obtained in step six is displayed on the deflection display module, and the pan-tilt position recording module records the horizontal position of the pan-tilt 23 at this time.

Step 8: Control the pan-tilt 23 to rotate horizontally through the pan-tilt control module, and repeat steps 2 to 7 for targets set on other points of the bridge to be measured, so as to detect the deflection of all points to be measured.

experiment analysis

In order to verify the accuracy of the deflection values measured by the detection system and detection method of the present invention, a total of five points to be measured were selected for deflection experiments. The measured result of the dial indicator is compared with the displayed deflection value (as table 1) of the deflection display module, by comparison, it can be known that the deflection value measured by the present invention can

enough to achieve the required measurement accuracy.

Table 1 Measurement results (θ ₂ =0.1°)

L target 52.185 59.643 64.750 68.382 73.356 f(L) value 0.0635 0.0722 0.0783 0.0827 0.0936 Δy 16.81978673 24.07420342 27.67563405 29.8222069 31.24350905 Y 1.068056507 1.738157568 2.167002247 2.466296625 2.924392583 dial gauge reading 0.986 1.833 2.236 2.372 2.831 Error (absolute value) 0.082056507 0.094842432 0.068997753 0.094296625 0.093392583

Claims (8)

1. a bridge deflection detection system, is characterized in that, comprises a plurality of targets (1), image acquisition device (2), laser ranging module (3), deflection calculation module and operating unit, wherein, image acquisition device (2 ) and the deflection calculation module are all connected with the operation unit; the image acquisition device (2) and the laser ranging module (3) are all connected with the deflection calculation module; A target (1) is respectively set at each point of the bridge to be tested; The image acquisition device (2) is used to acquire an initial image of the target (1) when the bridge to be tested is not loaded and a target image of the target (1) when the bridge to be tested is loaded; The laser ranging module (3) is used to measure the distance between the image acquisition device (2) and the target (1); The initial image, the target image and the distance between the image acquisition device (2) and the target (1) are all input into the deflection calculation module, and the deflection value at the point to be measured is calculated; The deflection value is transmitted to the operation unit by the deflection calculation module, and the operation unit displays the calculated deflection value; The image acquisition device (2) transmits the acquired real-time images to the operation unit, and the operation unit is used to control the image acquisition device (2) so that the image acquisition device (2) can acquire the image of the target (1). 2. bridge deflection detection system as claimed in claim 1, is characterized in that, described image acquisition device (2) comprises telescope optical system (21), area array CCD camera (22) and cloud platform (23), telescope optics The system (21) is installed on the top of the cloud platform (23), and the area array CCD camera (22) is installed on the rear of the telescope optical system (21) by a bracket. 3. The bridge deflection detection system according to claim 2, wherein the operating unit comprises an image display module, a deflection display module, a pan-tilt control module and a pan-tilt position recording module. 4. a method for bridge deflection detection using the bridge deflection detection system claimed in claim 3, is characterized in that, comprises the following steps: Step 1: Set a calibration plate on one side of the point to be measured of the bridge to be measured, and calibrate the bridge deflection detection system to obtain the distance L between the front end of the telescope optical system (21) and the calibration plate and the displacement represented by the unit pixel the functional relationship f(L) between the values; Step 2, area array CCD camera (22) obtains the real-time image of bridge to be measured, transmits to display in the described image display module; Adjust the tripod below the cloud platform (23), adjust the vertical position of the platform (23), and Utilize the cloud platform control module to adjust the horizontal position of the cloud platform (23), so that the image of the target (1) at the point to be measured is displayed in the image display module; Step 3, using the laser ranging module (3) to obtain the distance L _target between the front end of the telescope optical system (21) and the target (1), and deliver it to the deflection calculation module; Step 4, using the area array CCD camera (22) to collect the initial image P of the target (1) when the bridge is not under load, and deliver it to the deflection calculation module; Step 5, applying a load to the bridge, using the area array CCD camera (22) to collect the target image Q of the target (1) when the bridge is under load, and sending it to the deflection calculation module; Step 6, the deflection calculation module uses the distance L _target between the front end of the telescope optical system (21) and the target (1), the initial image P, the target image Q and the functional relationship f(L), to calculate the location of the target (1) The deflection of the bridge to be measured; Step 7, the deflection value obtained by step 6 is displayed on the deflection display module, and the cloud platform position recording module records the horizontal position where the cloud platform (23) is now; Step 8: Control the pan-tilt (23) to rotate horizontally through the pan-tilt control module, and repeat steps 2 to 7 for the targets (1) set on other points to be measured on the bridge, so as to detect the deflection of all points to be measured. 5. the method for bridge deflection detection as claimed in claim 4, is characterized in that, bridge deflection detection system in the described step 1 is demarcated, obtains the distance L between the telescope optical system (21) front end and the calibration plate and The functional relationship f(L) between the displacement values represented by the unit pixel specifically includes the following steps: Utilize the area array CCD camera (23) in the image acquisition device (2) to photograph the calibration plate, utilize the laser ranging module (3) to obtain the distance L between the front end of the telescope optical system (21) and the calibration plate; according to the calibration plate The number of pixels contained in the unit distance in the image is obtained, and the displacement value represented by the unit pixel is obtained under the distance L; the distance between the front end of the telescope optical system (21) and the calibration plate is changed many times to obtain different distances L In the case of , the displacement value represented by the unit pixel; Taking the distance L as the abscissa and the displacement value represented by the unit pixel as the ordinate, the functional relationship f(L) between the distance L and the displacement value represented by the unit pixel is obtained by fitting. 6. the method for bridge deflection detection as claimed in claim 5 is characterized in that, described utilizes laser ranging module (3) to obtain the distance L between the telescope optical system (21) front end and calibration plate, the formula that adopts as follows: θ = θ ₁ + θ ₂ L2=(a+L1)×cosθ L=L2-b Among them, a is the distance between the front end of the laser ranging module and its center point; b is the distance between the front end of the telescope optical system and its center point; L1 is the distance between the front end and the calibration plate measured by the laser ranging module; L2 is the distance between the center point of the telescope optical system and the calibration plate; θ ₁ is the angle between the laser ranging module and the horizontal direction; θ ₂ is the angle between the telescope optical system and the horizontal direction; θ is the laser ranging module The angle between the axis and the axis of the telescope optical system. 7. the method for bridge deflection detection as claimed in claim 4 is characterized in that, utilizes laser ranging module (3) in the described step 3 to obtain the distance between the telescope optical system (21) front end and the target (1) L _target , the formula adopted is as follows: θ = θ ₁ + θ ₂ L2=(a+L1)×cosθ L _target = L2-b Among them, a is the distance between the front end of the laser ranging module and its center point; b is the distance between the front end of the telescope optical system and its center point; L1 is the distance between the front end and the target measured by the laser ranging module; L2 is the distance between the center point of the telescope optical system and the target; θ ₁ is the angle between the laser ranging module and the horizontal direction; θ ₂ is the angle between the telescope optical system and the horizontal direction; θ is the axial direction of the laser ranging module Angle with the axis of the telescope optical system. 8. the method for bridge deflection detection as claimed in claim 4 is characterized in that, the deflection calculation module in the described step 6 utilizes the distance L _target , the initial image between the front end of the telescope optical system (21) and the target (1) P, target image Q and functional relationship f(L), calculate the deflection of the bridge to be measured point where the target (1) is located, comprising the following steps: Set up an m×n target surface coordinate system on the collected images in units of pixels; Obtain the vertical coordinates of the centers of the four solid circles on the initial image P as y ₁ , y ₂ , y ₃ , and y ₄ respectively, and calculate the vertical coordinate y of the target center position when the bridge is not under load: <mrow><mi>y</mi><mo>=</mo><mfrac><mn>1</mn><mn>4</mn></mfrac><mrow><mo>(</mo><msub><mi>y</mi><mn>1</mn></msub><mo>+</mo><msub><mi>y</mi><mn>2</mn></msub><mo>+</mo><msub><mi>y</mi><mn>3</mn></msub><mo>+</mo><msub><mi>y</mi><mn>4</mn></msub><mo>)</mo></mrow></mrow> Obtain the ordinates of the centers of the four solid circles on the target image Q as y ₁ ', y ₂ ', y ₃ ', y ₄ ' respectively, and calculate the ordinate y' of the center of the target when the bridge is under load: <mrow><msup><mi>y</mi><mo>,</mo></msup><mo>=</mo><mfrac><mn>1</mn><mn>4</mn></mfrac><mrow><mo>(</mo><msup><msub><mi>y</mi><mn>1</mn></msub><mo>,</mn>mo></msup><mo>+</mo><msup><msub><mi>y</mi><mn>2</mn></msub><mo>,</mo></msup><mo>+</mo><msup><msub><mi>y</mi><mn>3</mn></msub><mo>,</mo></msup><mo>+</mo><msup><msub><mi>y</mi><mn>4</mn></msub><mo>,</mo></msup><mo>)</mo></mrow></mrow> Calculate the number of pixels of the vertical offset of the target center position in the target surface coordinate system: Δy=y'-y Ask for the f (L) value when the distance between the front end of the telescope optical system (21) and the target (1) is the L _target ; Use the following formula to calculate the deflection projection value Y _{α of the deflection value at the target on the projection plane α} : Y _α =f(L)×Δy Then the deflection value Y at the target: Y _＝ Yα/ _cosθ2 Among them, _θ2 is the angle between the telescope optical system and the horizontal direction.