CN106705857A - Automatic monitoring system of laser surface displacement - Google Patents

Abstract

The invention discloses an automatic monitoring system of laser surface displacement. The automatic monitoring system of the laser surface displacement, disclosed by the invention, is monitoring equipment capable of meeting informatization construction requirements of geotechnical engineering. The automatic monitoring system comprises the following steps: step 1, a basic technological principle of the monitoring system; step 2, calibration of the monitoring system; step 3, estimation of displacement measurement precision; step 4, design of a measurement device. The automatic monitoring system is used for obtaining displacement changes of a surface on which a laser device is mounted through the variable quantity of an accurate coordinate of a light point formed by projecting an obtained laser point on a target plate, and a surface displacement monitoring problem of great quantity and wide range in foundation pit engineering and tunnel engineering is solved.

Description

A kind of laser surface displacement automatic monitoring system

Technical field

The invention belongs to automatic monitoring system technical field, it is related to a kind of laser surface displacement automatic monitoring system, is applicable In the surface displacement monitoring problem being had a large capacity and a wide range in base pit engineering, Tunnel Engineering monitoring.

Background technology

At present, Geotechnical Engineering monitoring is main based on manual measurement means, although have the automonitors such as hydrostatic level Device, but the market price is expensive so that in Geotechnical Engineering practice, it is impossible to which large-scale popularization is used.If moderate cost can be developed, The monitoring device that geotechnique informationization construction needs is disclosure satisfy that, its market prospects is huge.

Therefore, integrally it is considered as the sensor-based system that embedded system development energy on-line intelligence reads shift value.For reading Coordinate of the laser spots on target plate is taken, by investigation, there are several technological approaches, one kind is direct using PSD or CCD sensitive chips Photosensitive point coordinates is read, this method cost is higher.Also by optical fiber forming array, then one kind is using precision machining method Photosensitive point coordinates is read using array scanning, this method difficulty of processing is larger.A kind of last method is directly to use camera Photosensitive target plate is taken pictures, coordinate is read using photogrammetric survey method.A kind of last method cost is relatively low, will also be easily achieved, Plan carries out the development of automatic monitoring system in this way.

The content of the invention

The technical problems to be solved by the invention are the shortcomings for overcoming prior art, there is provided a kind of laser surface displacement is certainly Dynamic monitoring system, the purpose of the present invention is obtained by obtaining the variable quantity of the accurate coordinates of the luminous point that laser spots are incident upon on target plate To the surface displacement change for installing laser, the surface displacement being had a large capacity and a wide range in base pit engineering, Tunnel Engineering monitoring is solved Monitoring problem.

In order to solve the above technical problems, the present invention provides a kind of laser surface displacement automatic monitoring system, including it is following Step：

Step (1), the basic technique principle of monitoring system；

Using the collimation of laser, when A dot laser directive B points, a hot spot is there is on the target plate of B points, if B points (datum mark) transfixion, when A points are subjected to displacement, the hot spot on target plate is also accordingly moved.Accurate measurement target plate glazing The coordinate of point, you can obtain the size of A point displacements.And displacement can be obtained in horizontal displacement and vertical displacement both direction Value.

Laser is closed, the target plate RGB color image photo without luminous point is obtained, laser is opened, obtained with luminous point Target plate RGB color image photo, the camera pixel for using is 2592 × 1944.

Two target plate RGB color image photos are carried out into gray processing treatment respectively.

Gray scale picture after treatment is carried out into phase reducing, the image only having due to two images at bright spot is different, in phase After reducing, it may appear that obvious gray difference.

Image binaryzation treatment is carried out to this gray level image photo, binary-state threshold is the 80% of most bright spot gray value, is obtained The binary image for arriving.

In general, the round spot bright spot that laser is beaten is irregular, in order to accurately get to the coordinate bit of luminous point Put, corroded binary image using erosion algorithm, in order to accelerate erosion algorithm, experimental priori understands, The facular point pixel of laser is not more than 301 × 301, and carries out image interception；Binary image pixel size after interception No more than 301 × 301.

Now, binary image is corroded using erosion algorithm, selection corrosion matrix is as shown in formula：

Every time after corrosion, if image is not all 0, a preceding image is covered, if image is full 0, stop corrosion, do not covered Lid original image.

Bright spot pixel coordinate in image is averaged, that is, obtains the coordinate that laser is beaten on target plate.

Repeatedly obtain coordinate of the laser radiation on target plate, you can measurement obtains installing the body structure surface position of laser Move.

The demarcation of step (2), monitoring system；

The demarcation of monitoring system includes two parts, and first is the perspective demarcation of target plate, and second is the mark of pixel and distance It is fixed.

(1) perspective of target plate is demarcated

Target plate and measurement camera are arranged on measuring box, and due to technique, target plate and camera shooting face cannot It is substantially parallel, therefore the measurement apparatus need to carry out perspective demarcation after completing.

During target plate is made, one layer of squared paper of gauged distance is pasted, spacing is 10mm, is obtaining target plate After photo, 4 perspectives can be used to obtain perspective transform coefficient, the process of perspective transform is as follows：

(a), any one foursquare four summit on target plate photo is chosen, be successively upper left, upper right, lower-left, bottom right, Obtain its pixel coordinate (xZS, yZS), (xYS, yYS), (xZX, yZX), (xYX, yYX)；

(b), obtain that new rectangle is wide and height from former quadrangle according to formula；

Four apex coordinates after then converting are as shown in formula：

(c), make B=[X (1), Y (1), X (2), Y (2), X (3), Y (3), X (4), Y (4)]^T, matrix of the solution as shown in formula Equation：

Order

Perspective transform coefficient is obtained as shown in formula：

Xi=inv (A) B * MERGEFORMAT (6)

Wherein, Xi is 8 × 1 rank matrixes, so as to obtain conversion coefficient as shown in formula：

(d), assume that the light point coordinates that erosion algorithm draws is (x₀, y₀), then need to carry out perspective transform according to formula, obtain Final coordinate.

So far, perspective transform is completed.

(2) demarcation of pixel distance

, it is necessary to obtain the corresponding relation of pixel distance and actual range after the perspective demarcation of target plate terminates, according to target plate On normal line, choose two point coordinates (x of distance_1o, y_1o), (x_2o, y_2o), it is known that its distance is L, using conversion coefficient Its coordinate is transformed to (x₁, y₁), (x₂, y₂), then distance calibration coefficient is as shown in formula：

According to this coefficient, the displacement of laser optical pair twice can be obtained.

Step (3), assessment displacement measurement accuracy；

It is 2592 × 1944 that measurement camera shoots pixel, and target plate size is 133mm × 100mm, both ratios such as formula institute Formula：

Therefore, theoretically see, every 2 points of pixel distance is 100/1944<0.052mm, it is considered to the barycentric coodinates of hot spot The influence such as searching and alignment error, the measurement apparatus displacement measurement accuracy needs the determination in actual stability test.

Step (4), the design of measurement apparatus；

(1) design of box body, is measured

Measurement box body material uses 6061-T6 alloy aluminums, category heat treatment can reinforced alloys, with good formability, Weldability, machinable, while having moderate strength, remain to maintain preferable operability, the small quality of density after annealing Gently, anticorrosion is easy to install.

Box body uses splicing structure, and main body is made up of six blocks of sheet materials.

Tray interior installs adjustable support, is designed using draw-in groove, for installing measurement camera.Box body two ends are using slotting Groove is designed, and target plate is shot for inserting.

(2) design of target plate, is measured

The material for measuring target plate is made using common are machine plastic plate on the market, and sheet metal thickness 2mm, white, printing opacity is micro- It is transparent.The organic plastic plate has excellent toughness and dimensional stability, and insulating properties are reliable, heat resistance is good, acid and alkali-resistance, anti- Chemical attack, easily processes, and asepsis environment-protecting, durable in use.One layer of plastics of gauged distance grid can be in the above pasted, For the demarcation of measuring system.

(3) design of hardware, is measured

Measurement hardware uses Raspberry Pi card form computer Type B Rev1, and its volume only has size as credit card, has There are the functions such as video, network, IO.

The run time is measured each time in Raspberry Pi platforms to be about 5 seconds, shown that measurement frequency is reachable To 0.2Hz, in the measurement of the surface displacements such as actual foundation ditch, tunnel, due to surface displacement change slowly, the measurement Frequency fully meets measurement request.

The beneficial effects of the invention are as follows：The method of present invention design is realized suitable for being supervised in base pit engineering, Tunnel Engineering The surface displacement automatic monitoring system being had a large capacity and a wide range in survey, reduces monitoring cost, can unattended automatic acquisition surface displacement Information, is base pit engineering, the major progress of Tunnel Engineering monitoring technical field.

Brief description of the drawings

Fig. 1 is principle flow chart of the invention；

Fig. 2 is the basic technique principle schematic diagram of monitoring system；

Fig. 3 (a) is to close the target plate RGB color image photo acquired in laser；

Fig. 3 (b) is to open the target plate RGB color image photo acquired in laser；

Fig. 4 (a) is to close the target plate gray level image photo acquired in laser；

Fig. 4 (b) is to open the target plate gray level image photo acquired in laser；

Fig. 5 is the target plate gray level image photo after mutually cutting algorithm；

Fig. 6 is binary image result；

Fig. 7 is to take hot spot scope flow chart of steps；

Fig. 8 is the spot area binaryzation picture after interception；

Fig. 9 is erosion algorithm process picture；

Figure 10 (a) is the target plate photo parallel with camera shooting face in ideal；

Figure 10 (b) is that actual target plate shoots the not parallel photo in face with camera；

Figure 11 is measurement box body construction diagrams；

Figure 12 is the draw-in groove design of measurement box body adjustable camera support；

Figure 13 is measurement hardware block diagram；

Figure 14 is measurement hardware automatic running program block diagram；

Figure 15 is monitoring system flow；

Figure 16 (a) is stability test result scattergram；

Figure 16 (b) is stability test result block diagram；

Figure 17 is displacement platform square path measurements result schematic diagram.

Specific embodiment

Embodiment 1

The present embodiment provides a kind of laser surface displacement automatic monitoring system, and principle is as shown in figure 1, comprise the following steps：

Step (1), the basic technique principle of monitoring system；

As shown in Fig. 2 using the collimation of laser, when A dot laser directive B points, a light is there is on the target plate of B points Spot, if B point (datum mark) transfixion, when A points are subjected to displacement, the hot spot on target plate is also accordingly moved.It is accurate to survey The coordinate of luminous point on amount target plate, you can obtain the size of A point displacements.And can be in horizontal displacement and vertical displacement both direction Upper acquisition shift value.

Laser is closed, the target plate RGB color image photo without luminous point is obtained, shown in such as Fig. 3 (a), laser is opened, The target plate RGB color image photo with luminous point is obtained, such as shown in 3 (b), the camera pixel for using is 2592 × 1944.

Two target plate RGB color image photos are carried out into gray processing treatment respectively, shown in such as Fig. 4 (a) and Fig. 4 (b).

Gray scale picture after treatment is carried out into phase reducing, the image only having due to two images at bright spot is different, in phase After reducing, it may appear that obvious gray difference, as shown in Figure 5.

Image binaryzation treatment is carried out to this gray level image photo, binary-state threshold is the 80% of most bright spot gray value, is obtained The binary image for arriving is as shown in Figure 6.

In general, the round spot bright spot that laser is beaten is irregular, in order to accurately get to the coordinate bit of luminous point Put, corroded binary image using erosion algorithm, in order to accelerate erosion algorithm, experimental priori understands, The facular point pixel of laser is not more than 301 × 301, method can carry out image interception as shown in Figure 7.

Binary image pixel size after interception is not more than 301 × 301, as shown in Figure 8.

Now, binary image is corroded using erosion algorithm, selection corrosion matrix is as shown in formula：

Every time after corrosion, if image is not all 0, a preceding image is covered, if image is full 0, stop corrosion, do not covered Lid original image, as shown in Figure 9.

Bright spot pixel coordinate in image is averaged, that is, obtains the coordinate that laser is beaten on target plate.

Repeatedly obtain coordinate of the laser radiation on target plate, you can measurement obtains installing the body structure surface position of laser Move.

The demarcation of step (2), monitoring system；

The demarcation of monitoring system includes two parts, and first is the perspective demarcation of target plate, and second is the mark of pixel and distance It is fixed.

(1) perspective of target plate is demarcated

Target plate and measurement camera are arranged on measuring box, and due to technique, target plate and camera shooting face cannot It is substantially parallel, as shown in Figure 10, therefore the measurement apparatus need to carry out perspective demarcation after completing.

During target plate is made, one layer of squared paper of gauged distance is pasted, spacing is 10mm, is obtaining target plate After photo, 4 perspectives can be used to obtain perspective transform coefficient, the process of perspective transform is as follows：

(a), any one foursquare four summit on target plate photo is chosen, be successively upper left, upper right, lower-left, bottom right, Obtain its pixel coordinate (xZS, yZS), (xYS, yYS), (xZX, yZX), (xYX, yYX)；

(b), obtain that new rectangle is wide and height from former quadrangle according to formula；

Four apex coordinates after then converting are as shown in formula：

(c), make B=[X (1), Y (1), X (2), Y (2), X (3), Y (3), X (4), Y (4)]^T, matrix of the solution as shown in formula Equation：

Order

Perspective transform coefficient is obtained as shown in formula：

Xi=inv (A) B * MERGEFORMAT (6)

Wherein, Xi is 8 × 1 rank matrixes, so as to obtain conversion coefficient as shown in formula：

(d), assume that the light point coordinates that erosion algorithm draws is (x₀, y₀), then need to carry out perspective transform according to formula, obtain Final coordinate.

So far, perspective transform is completed.

(2) demarcation of pixel distance

, it is necessary to obtain the corresponding relation of pixel distance and actual range after the perspective demarcation of target plate terminates, according to target plate On normal line, choose two point coordinates (x of distance_1o, y_1o), (x_2o, y_2o), it is known that its distance is L, using conversion coefficient Its coordinate is transformed to (x₁, y₁), (x₂, y₂), then distance calibration coefficient is as shown in formula：

According to this coefficient, the displacement of laser optical pair twice can be obtained.

Step (3), assessment displacement measurement accuracy；

It is 2592 × 1944 that measurement camera shoots pixel, and target plate size is 133mm × 100mm, both ratios such as formula institute Formula：

Therefore, theoretically see, every 2 points of pixel distance is 100/1944<0.052mm, it is considered to the barycentric coodinates of hot spot The influence such as searching and alignment error, the measurement apparatus displacement measurement accuracy needs the determination in actual stability test.

Step (4), the design of measurement apparatus；

(1) design of box body, is measured

Measurement box body material uses 6061-T6 alloy aluminums, category heat treatment can reinforced alloys, with good formability, Weldability, machinable, while having moderate strength, remain to maintain preferable operability, the small quality of density after annealing Gently, anticorrosion is easy to install.

Box body uses splicing structure, and main body is made up of six blocks of sheet materials, as shown in figure 11.

Tray interior installs adjustable support, is designed using draw-in groove, for installing measurement camera.Box body two ends are using slotting Groove is designed, and target plate is shot for inserting；As shown in figure 12.

(2) design of target plate, is measured

The material for measuring target plate is made using common are machine plastic plate on the market, and sheet metal thickness 2mm, white, printing opacity is micro- It is transparent.The organic plastic plate has excellent toughness and dimensional stability, and insulating properties are reliable, heat resistance is good, acid and alkali-resistance, anti- Chemical attack, easily processes, and asepsis environment-protecting, durable in use.One layer of plastics of gauged distance grid can be in the above pasted, For the demarcation of measuring system.

(3) design of hardware, is measured

Measurement hardware uses Raspberry Pi card form computer Type B Rev1, and its volume only has size as credit card, has There are the functions such as video, network, IO, hardware block diagram is as shown in figure 13.

As shown in figure 14, measured the run time each time in Raspberry Pi platforms to be about 5 seconds, show to survey Amount frequency can reach 0.2Hz, in the measurement of the surface displacements such as actual foundation ditch, tunnel, due to surface displacement change very Slowly, the measurement frequency fully meets measurement request.

Technical scheme is described in detail below with reference to accompanying drawing 15-17：

Flow as shown in figure 15, is first had to produce measuring box and target plate, and then burning is compiled well on Raspberry Pi The process of measurement write, determines the distance of camera and target plate, puts up measuring table, then shoots initial photo, has an X-rayed Conversion solves calibration factor, determines the relation of pixel distance and experiment distance, finally carries out stability test, obtains actual survey Accuracy of measurement.

Implementation process will be extracted to the coordinate of laser pixel in technical scheme by specific example below It is explained.

After measuring box is installed, you can carry out perspective transform demarcation, calculate transformation factor, determine pixel distance with The relation of actual range.Foursquare four summit arbitrarily is taken, finally calculating the perspective transform factor is：

A=0.96142384

B=0.00401253

C=168.45083955

D=-0.01557080

E=0.98860270

F=-149.21030551

G=-0.00001872

H=0.00000839

Actual range draw per adjacent two pixel simultaneously between is 0.04755435mm

These parameters and process of measurement are imported in measurement hardware, that is, completes the preparation of measurement hardware-software.

In the installation process of the laser surface displacement automatic monitoring system, have defined below to mounting condition：

Distance, away from too far away, is difficult to adjust laser luminous point to target plate no more than 10 meters between laser and measuring box On, it is the target plate that flies out that twisting luminous point slightly occurs in laser.

Measuring box needs remains stationary, and parallel to displacement surface, laser light vertically and displacement surface simultaneously in target plate face With target plate surface.

Laser is arranged on precision displacement platform, can carry out three motions in direction with displacement platform, for this certainly Dynamic monitoring system, it is only necessary to moved on the surface perpendicular to horizontal plane, it is 1 μm that displacement platform displacement is accurate. When the laser is turned off, monitoring system can shoot a photo, and laser then can be controlled to open, and then measuring system can be by two Width picture carries out gray proces, binary conversion treatment, and intercepting most bright spot near zone after being subtracted each other again carries out corrosion treatment, until Can not corrode.The average coordinates of last residue bright spot are to be considered laser into the pixel coordinate on target plate.

In the stability test of measuring system, keep laser positions constant, continuously done the measurement of 1000 times, obtain Result as shown in figure 16, in Figure 16 (a) it can be seen that hormone bright spot is concentrated within the square of 6 pixels.Take this point Centered on the average value of pixel, pixel distance distribution probability such as Figure 16 (b) institute of each measurement result apart from this central point Show, it can be seen that the distance at each pixel of pixel and center is 99.8% less than 3 probability of pixel, less than 4 pixels Probability is 100%, you can with the displacement measurement accuracy for thinking this monitoring system be 4 pixels, with reference to adjacent in calibration result Actual range between two pixels, it can be deduced that the certainty of measurement of the automatic monitoring system is 4 × 0.04755435<0.2mm.

In actual measurement experiment, command displacement platform carries out a square path and moves, each displacement 1mm, most Whole measurement result is as shown in figure 17.

Above example is only explanation technological thought of the invention, it is impossible to limit protection scope of the present invention with this, every According to technological thought proposed by the present invention, any change done on the basis of technical scheme each falls within the scope of the present invention Within.

Claims (9)

1. a kind of laser surface displacement automatic monitoring system, it is characterised in that including step in detail below：

Step (1), the basic technique principle of monitoring system；

Using the collimation of laser, when A dot laser directive B points, a hot spot is there is on the target plate of B points, if B points are base Transfixion on schedule, when A points are subjected to displacement, the hot spot on target plate is also accordingly moved；Luminous point on accurate measurement target plate Coordinate, you can obtain the size of A point displacements；And shift value can be obtained in horizontal displacement and vertical displacement both direction；

Laser is closed, the target plate RGB color image photo without luminous point is obtained, laser is opened, the target plate with luminous point is obtained RGB color image photo；

Two target plate RGB color image photos are carried out into gray processing treatment respectively；

Gray scale picture after treatment is carried out into phase reducing, the image only having due to two images at bright spot is different, is subtracting each other behaviour After work, it may appear that obvious gray difference；

Image binaryzation treatment is carried out to this gray level image photo, the binary image for obtaining；

Now, binary image is corroded using erosion algorithm, selection corrosion matrix is as shown in formula：

$\begin{array}{cc}b=\left[\begin{array}{ccc}0& 1& 0\\ 1& 1& 1\\ 0& 1& 0\end{array}\right]& \backslash *MERGEFORMAT\end{array}---\left(1\right)$

Bright spot pixel coordinate in image is averaged, that is, obtains the coordinate that laser is beaten on target plate；

Repeatedly obtain coordinate of the laser radiation on target plate, you can measurement obtains installing the body structure surface displacement of laser；

The demarcation of step (2), monitoring system；

The demarcation of monitoring system includes：The perspective of target plate is demarcated, the demarcation of pixel and distance；

(1) perspective of target plate is demarcated

Target plate and measurement camera are arranged on measuring box, and perspective demarcation is carried out after measurement apparatus complete；

Make target plate during, paste one layer of squared paper of gauged distance, after target plate photo is obtained, can be used 4 points it is saturating Perspective transform coefficient is obtained depending on method, the process of perspective transform is as follows：

(a), any one foursquare four summit on target plate photo is chosen, be successively upper left, upper right, lower-left, bottom right, acquisition Its pixel coordinate (xZS, yZS), (xYS, yYS), (xZX, yZX), (xYX, yYX)；

(b), obtain that new rectangle is wide and height from former quadrangle according to formula:

$\begin{array}{cc}\begin{array}{c}w=round\left(\sqrt{{\left(xZS-xYS\right)}^2+{\left(yZS-yYS\right)}^2}\right)\\ h=round\left(\sqrt{{\left(xZS-xZX\right)}^2+{\left(yZS-yZX\right)}^2}\right)\end{array}& \backslash *MERGEFORMAT\end{array}---\left(2\right)$

Four apex coordinates after then converting are as shown in formula：

$\begin{array}{cc}\begin{array}{c}X=\left(xZS,xZS+w,xZS,xZS+w\right)\\ Y=\left(yZS,yZS,yZS+h,yZS+h\right)\end{array}& \backslash *MERGEFORMAT\end{array}---\left(3\right)$

(c), make B=[X (1), Y (1), X (2), Y (2), X (3), Y (3), X (4), Y (4)]^T, matrix equation of the solution as shown in formula：

$\begin{array}{c}\left[\begin{array}{cccccccc}xZS& yZS& 1& 0& 0& 0& -X\left(1\right)*xZS& -X\left(1\right)*yZS\\ 0& 0& 0& xZS& yZS& 1& -Y\left(1\right)*xZS& -Y\left(1\right)*yZS\\ xZS& yZS& 1& 0& 0& 0& -X\left(2\right)*xYS& -X\left(2\right)*yYS\\ 0& 0& 0& xYS& yYS& 1& -Y\left(2\right)*xYS& -Y\left(2\right)*yYS\\ xZX& yZX& 1& 0& 0& 0& -X\left(3\right)*xZX& -X\left(3\right)*yZX\\ 0& 0& 0& xZX& yZX& 1& -Y\left(3\right)*xZX& -Y\left(3\right)*yZX\\ xYX& yYZ& 1& 0& 0& 0& -X\left(4\right)*xYX& -X\left(4\right)*yYX\\ 0& 0& 0& xYX& yYX& 1& -Y\left(4\right)*xYX& -Y\left(4\right)*yYX\end{array}\right]\&CenterDot;Xi=B\\ \backslash *MERGEFORMAT\end{array}---\left(4\right)$

Order

$\begin{array}{c}A=\left[\begin{array}{cccccccc}xZS& yZS& 1& 0& 0& 0& -X\left(1\right)*xZS& -X\left(1\right)*yZS\\ 0& 0& 0& xZS& yZS& 1& -Y\left(1\right)*xZS& -Y\left(1\right)*yZS\\ xZS& yZS& 1& 0& 0& 0& -X\left(2\right)*xYS& -X\left(2\right)*yYS\\ 0& 0& 0& xYS& yYS& 1& -Y\left(2\right)*xYS& -Y\left(2\right)*yYS\\ xZX& yZX& 1& 0& 0& 0& -X\left(3\right)*xZX& -X\left(3\right)*yZX\\ 0& 0& 0& xZX& yZX& 1& -Y\left(3\right)*xZX& -Y\left(3\right)*yZX\\ xYX& yYZ& 1& 0& 0& 0& -X\left(4\right)*xYX& -X\left(4\right)*yYX\\ 0& 0& 0& xYX& yYX& 1& -Y\left(4\right)*xYX& -Y\left(4\right)*yYX\end{array}\right]\\ \backslash *MERGEFORMAT\end{array}---\left(5\right)$

Perspective transform coefficient is obtained as shown in formula：

Xi=inv (A) B * MERGEFORMAT (6)

Wherein, Xi is 8 × 1 rank matrixes, so as to obtain conversion coefficient as shown in formula：

$\begin{array}{cc}\begin{array}{ccc}a=Xi\left(1\right)& b=Xi\left(2\right)& c=Xi\left(3\right)\\ d=Xi\left(4\right)& e=Xi\left(5\right)& f=Xi\left(6\right)\\ g=Xi\left(7\right)& h=Xi\left(8\right)& \end{array}& \backslash *MERGEFORMAT\end{array}---\left(7\right)$

(d), assume that the light point coordinates that erosion algorithm draws is (x₀, y₀), then need to carry out perspective transform according to formula, obtain final Coordinate：

$\begin{array}{cc}\begin{array}{c}x=\frac{d\&CenterDot;x_0+e\&CenterDot;y_0+f}{g\&CenterDot;x_0+h\&CenterDot;y_0+1}\\ y=\frac{a\&CenterDot;x_0+b\&CenterDot;y_0+c}{g\&CenterDot;x_0+h\&CenterDot;y_0+1}\end{array}& \backslash *MERGEFORMAT\end{array}---\left(8\right)$

So far, perspective transform is completed；

(2) demarcation of pixel distance

, it is necessary to obtain the corresponding relation of pixel distance and actual range after the perspective demarcation of target plate terminates, according on target plate Normal line, chooses two point coordinates (x of distance_1o, y_1o), (x_2o, y_2o), it is known that its distance be L, using conversion coefficient by its Coordinate is transformed to (x₁, y₁), (x₂, y₂), then distance calibration coefficient is as shown in formula：

$\begin{array}{cc}{b}_d=\frac{L}{\sqrt{{(x_1-x_2)}^2+{(y_1-y_2)}^2}}& \backslash *MERGEFORMAT\end{array}---\left(9\right)$

According to this coefficient, the displacement of laser optical pair twice can be obtained；

Step (3), assessment displacement measurement accuracy；

Step (4), the design of measurement apparatus；

(1) design of box body, is measured

Measurement box body uses splicing structure, and main body is made up of six blocks of sheet materials, and tray interior installs adjustable support, is set using draw-in groove Meter, for installing measurement camera, box body two ends use socket designs, and target plate is shot for inserting；

(2) design of target plate, is measured

Measurement target plate is organic plastic plate, and sheet metal thickness 2mm, white, printing opacity is sub-translucent, and its upper surface pastes one layer of gauged distance The plastics of grid；

(3) design of hardware, is measured

Measurement hardware uses Raspberry Pi card form computer Type Bs Rev1；

The run time is measured each time in Raspberry Pi platforms to be about 5 seconds, shown that measurement frequency can reach 0.2Hz, in the measurement of the surface displacements such as actual foundation ditch, tunnel, due to surface displacement change slowly, the measurement is frequently Rate fully meets measurement request.

2. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (1), The camera pixel that acquisition target plate RGB color image photo is used is 2592 × 1944.

3. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (1), Binary-state threshold is the 80% of most bright spot gray value.

4. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (1), Generally, the round spot bright spot that laser is beaten is irregular, in order to accurately get to the coordinate position of luminous point, uses corrosion Algorithm is corroded binary image, and in order to accelerate erosion algorithm, the facular point pixel of laser is not more than 301 × 301, And carry out image interception；Binary image pixel size after interception is not more than 301 × 301.

5. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (1), Every time after corrosion, if image is not all 0, a preceding image is covered, if image is full 0, stop corrosion, do not cover artwork Picture.

6. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (2), The compartment of the squared paper of described gauged distance is away from being 10mm.

7. laser surface displacement automatic monitoring system according to claim 2, it is characterised in that in the step (3), Assess displacement measurement accuracy specific method be：Measurement camera shoot pixel be 2592 × 1944, target plate size be 133mm × 100mm, both ratios such as formula depicted：

$\begin{array}{cc}\frac{2592}{1944}=\frac{4}{3}\&ap;\frac{133}{100}& \backslash *MERGEFORMAT\end{array}---\left(10\right)$

Then, every 2 points of pixel distance is 100/1944<0.052mm, it is considered to the barycentric coodinates searching of hot spot and alignment error etc. Influence, the measurement apparatus displacement measurement accuracy need to then determine in actual stability test.

8. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (4), Measurement box body material uses 6061-T6 alloy aluminums.

9. laser surface displacement automatic monitoring system according to claim 1, it is characterised in that in the step (4), The measurement target plate thickness is 2mm, and white, printing opacity is sub-translucent.