CN102620662A - Light curtain-based vehicle size automatic measuring system and measuring method thereof - Google Patents

Abstract

The invention relates to a light curtain-based vehicle size automatic measuring system and a measuring method thereof. The system consists of a measuring host, a signal acquisition device and a light curtain sensor array which are connected, wherein the light curtain sensor array is a three-dimensional structure which consists of a height measuring light curtain sensor, a width measuring light curtain sensor and a length measuring light curtain sensor; output ends of the height measuring light curtain sensor, the width measuring light curtain sensor and the length measuring light curtain sensor are connected with the signal acquisition device; and after a detection signal transmitted by the light curtain sensor array is received by the measuring host, the height, the width and the length of a vehicle to be measured are calculated by the measuring host. The system is rational in design; an accurate measuring function of the vehicle size is realized; the problem of error in image contour dimension caused by the fact that a camera screenshot is not in the same plane as a land mark and a vertical mark existing in a camera image photograph measuring method is solved; the measuring accuracy and stability are improved; and all the degree of difficulty for handling, the anti-interference capacity and the maintainability are dramatically improved.

Description

Vehicle dimension automatic measurement system and measuring method thereof based on the light curtain

Technical field

The present invention relates to a kind of vehicle dimension detection system, especially a kind of vehicle dimension automatic measurement system and measuring method thereof based on the light curtain.

Background technology

Developing of automobile industry has greatly promoted The development in society and economy, but also therefore brings a lot of traffic problems.In the frequent traffic hazard that takes place in every year; The ratio that causes following traffic hazard because of the vehicle overall dimensions constantly rises: the vehicle user that part is used for visitor/shipping purposes is in order to obtain bigger economic interests; Through reequiping vehicle dimension to increase the vehicle volume; Reaching increases the purpose that the disposable transportation of vehicle reduces transportation cost, and the safety standard that vehicle uses has seriously been violated in this behave, because the goods that the vehicle of super large overall dimensions is reprinted is also bigger; When the bridge through having less holding capacity or width of roadway do not allow two ultra wide vehicles parallel, often do not cause danger, the annual traffic hazard that takes place because of overload of vehicle is of common occurrence.In order to guarantee the security of vehicle, vehicle all must carry out annual test every year, still, carries out with the manual measurement mode often when detecting vehicle dimension at present, and the problem of its existence is: 1, the testing result error is bigger, can't guarantee the accuracy of measuring; 2, detection time longer, inefficiency, and take more human and material resources; 3, automaticity is low, can not satisfy the growth requirement of motor vehicle management department to the management of motorized vehicles implementation information.To the problems referred to above, present main solution is that the method that adopts camera review to capture is obtained vehicle overall size.

Number of patent application is to have provided " based on the vehicle overall dimensions detection system of image processing " in 03114546.9 the document; It obtains front elevation, side view, vertical view three width of cloth contours of the vehicle image through the image acquisition unit; Get into storer, digital processing unit reads in three width of cloth contour of the vehicle pictorial data successively from storer, through the motor vehicles appearance image is analyzed; Obtain the height and the width of vehicle from the front elevation of vehicle; Obtain the height and the length of vehicle from the side view of vehicle, obtain the width and the length of vehicle, detected three groups of data are carried out weighted mean draw and have reliable and accurate vehicle overall dimensions from the vertical view of vehicle.Though this technical scheme can access the physical dimension of motor vehicles,, the problem of its existence is: limited by gamma camera optimal viewing angle and coverage, also there is error in the motor vehicle physical dimension of picked-up; 2, lack tangible object of reference in this technical scheme and look like to carry out the parameter correction, make testing result have error.

Patent documentation ZL200920079045.7 has proposed " obtaining the Automatic Measuring Apparatus of vehicle image metering vehicle contour dimension in the motion; its implementation is: through falling " L " side and the top of shape column steelframe install two or more sets video cameras passing vehicle taken; thereby obtain the side view and the vertical view of vehicle; and splice the length that obtains vehicle at last again through continuous image shooting in imaginary Virtual Space; and; its survey wide mechanism with survey high, gauging machine structure according in the captured picture to the situation of blocking of ground mark and facade mark, the both sides that from picture, are not blocked or up and down between distance values obtain the actual width of vehicle or highly.Though this technical scheme can both realize the measurement to the motor vehicles shell sizes; But the problem of its existence is: 1, captured vehicle overlook sectional drawing, side-looking sectional drawing because and its corresponding survey is wide, it is high to survey, survey the long denotation thing not in same plane, its measurement result has tended to error; For example; When vehicle is not vertical row and then angle presentation deviation when advancing, or the position that is taken of vehicle is not when reaching the object distance scope that constitutes sharp image, surveys that distance draws vehicle width between the both sides that wide mechanism is not blocked from high vertical view; Often be not the width of vehicle, in like manner drawing in this way, the height of measuring vehicle also has error;Thereby 2, when clap picture and piece together when going back the map interlinking sheet and obtaining the length of vehicle in a certain zone through connecting; Often cause the face image to have distortion or distortion owing to dynamically connect bat; Then can't realize seamless spliced between the image, thus can not be accurate the calculate vehicle length dimension.

In sum; There is following problem in the method that adopts video camera to capture image and then measuring vehicle physical dimension: 1, when adopting survey mark object space method to measure; Because surface mark thing or facade mark not in a plane, cause image physical dimension error with the sectional drawing of captured image; 2, receive the restriction of video camera optimal viewing angle and coverage, often there is error in captured image; 3, when adopting ground reference to measure,, make Flame Image Process, analytic process complicated, thereby increased the measurement difficulty owing to lack clearly with reference to the parameter correction of image as measuring vehicle physical dimension.

Summary of the invention

The objective of the invention is to overcome the deficiency of prior art, provide a kind of reasonable in design, measuring accuracy is high and the vehicle dimension automatic measurement system and the measuring method thereof based on the light curtain of convenient measurement.

The present invention solves its technical matters and takes following technical scheme to realize:

A kind of vehicle dimension automatic measurement system based on the light curtain; Connect and compose by measurement host, signal pickup assembly and light curtain sensor array; Described smooth curtain sensor array is the spatial structure that is made up of the high light curtain sensor of survey, the wide smooth curtain sensor of survey, the long light curtain sensor of survey; The output terminal of surveying high light curtain sensor, the wide smooth curtain sensor of survey, the long light curtain sensor of survey is connected with signal pickup assembly, calculates height of car to be measured, vehicle width, length behind the detection signal that measurement host reception light curtain sensor array transmits.

And the high light curtain sensor of described survey comprises an illuminator L1 and the light receiving device S1 corresponding with it, and this is surveyed high light curtain sensor and is installed in relatively in the Z axial plane perpendicular to ground; The long light curtain sensor of described survey comprises two illuminator L2, L3 and two light receiving device S2s, the S3 corresponding with it, and two illuminator L2, L3 and two light receiving device S2, S3 are installed in respectively in the X axial plane that is parallel to ground relatively; The wide smooth curtain sensor of described survey comprises two illuminator L4, L5 and two light receiving device S4, S5, and two illuminator L4, L5 and two light receiving device S4, S5 are installed in respectively between upper and lower two planes of forming perpendicular to the Z axle and by X axle, Y axle relatively.

And; Described smooth curtain sensor array also comprises a location appearance light curtain sensor; This location appearance light curtain sensor comprises the wide smooth curtain sensor of survey that two rows are parallel to each other; The installation site that every row surveys wide smooth curtain sensor is: upper edge, the plane X-direction being made up of Y axle, X axle is drawn a center line, and each each one group of light curtain sensor of discharging straggly is parallel along X-direction between two groups of light curtain sensors along front and back, center line both sides; Along Y direction, with the center line be the boundary each other from a distance, form the unglazed curtain zone along X-direction of an elongate in shape.

And described signal pickup assembly is plugged in the measurement host and through serial ports with built-in method and is connected with the high light curtain sensor of survey, the wide smooth curtain sensor of survey, the long light curtain sensor of survey and location appearance light curtain sensor.

And described signal pickup assembly is connected with measurement host through serial ports or network interface with external method and is connected with the high light curtain sensor of survey, the wide smooth curtain sensor of survey, the long light curtain sensor of survey and location appearance light curtain sensor through serial ports.

And described measurement host also is connected to be used to detect whether remain to be surveyed the work of vehicle with the control signal collector with a parking stall measure sensor.

A kind of vehicle dimension method for automatic measurement based on the light curtain may further comprise the steps:

Step 1:, detect whether remain to be surveyed vehicle through the parking stall measure sensor of burying underground in advance;

Step 2: if detect vehicle to be measured, signal picker will trigger light curtain sensor array and start working;

Step 3: when vehicle to be measured gets into light curtain sensor array; In a collection period through surveying high light curtain sensor, location appearance light curtain sensor and surveying the wide corresponding signal of smooth curtain sensor collection and send measurement host to, by measurement host measuring vehicle height, vehicle pose and vehicle width;

Step 4: when vehicle to be measured remains static and fall into the light curtain zone of measuring vehicle length, survey long light curtain sensor acquired signal and send measurement host to, carry out measuring vehicle length by measurement host.

And the method for measuring vehicle height is in the said step 3: when vehicle to be measured gets into when surveying high light curtain sensor scope, along the be blocked extreme higher position of optical axis of Z-direction;

The measuring vehicle pose obtains through following calculated with mathematical model in the said step 3:

tagθ＝(H2-H1)/LT1

In the formula: θ is the vehicle pose, and H1 is the distance that center line is ordered to a, and a point is that a location appearance light curtain sensor light curtain is along maximal value on the Y direction; H2 is the distance that center line is ordered to b, and the b point is that another location appearance light curtain sensor is along maximal value on the Y direction; LT1 is the distance of two location appearance light curtain sensors;

The measuring vehicle width W obtains through following computation model in the said step 3:

W＝cosθ*LT4

Wherein, θ is the vehicle pose, and the length value of LT4 equals the distance between a, the d, and a, d are the be blocked maximal value of optical axis of the minimum value of the optical axis that is blocked along Y direction light curtain and light curtain.

And measuring vehicle length L T adopts following calculated with mathematical model to obtain in the said step 4:

LT＝S2/cosθ

In the formula, ST2=ST-ST1, the ST value equals along the distance between X-direction a, the b, and a is the minimum value along X-direction light curtain, and b is the maximal value along X-direction light curtain;

ST1=sin θ * W, W is a vehicle width.

Advantage of the present invention and good effect are:

The present invention is reasonable in design; Through survey high light curtain sensor, survey wide smooth curtain sensor, the long light curtain sensor of survey treats the survey vehicle and carries out the detection of height of car, width, length; Detect through the attitude of location appearance light curtain sensor simultaneously vehicle; Again according to the attitude of vehicle to the length of vehicle, effective compensation that width carries out the angle of inclination; Thereby realized accurate measurement function to vehicle dimension; Solved the take pictures error of the image physical dimension that measuring method do not cause because of shooting sectional drawing and surface mark thing and facade mark of camera review in same plane, improved measuring accuracy and stability, all increased significantly from handling easy degree, antijamming capability and maintainability.

Description of drawings

Fig. 1 is that system of the present invention connects synoptic diagram;

Fig. 2 is the mounting arrangement synoptic diagram of four kinds of light curtain sensors;

Fig. 3 is a measuring method processing flow chart of the present invention;

Fig. 4 is the principle schematic of measuring vehicle height;

Fig. 5 is the schematic layout pattern of location appearance light curtain sensor;

Fig. 6 is the principle schematic of measuring vehicle pose;

Fig. 7 is the principle schematic (pose angle θ is zero) of measuring vehicle width;

Fig. 8 is the principle schematic (θ is non-vanishing for the pose angle) of measuring vehicle width;

Fig. 9 is the principle schematic (pose angle θ is zero) of measuring vehicle length;

Figure 10 is the principle schematic (θ is non-vanishing for the pose angle) of measuring vehicle length.

Embodiment

Below in conjunction with accompanying drawing the embodiment of the invention is done further detailed description:

A kind of vehicle dimension automatic measurement system based on the light curtain; As shown in Figure 1; Connect and compose by measurement host, signal pickup assembly and light curtain sensor array; This light curtain sensor array is by surveying high light curtain sensor, surveying the spatial structure that wide smooth curtain sensor, the long light curtain sensor of survey and location appearance light curtain sensor constitute; Survey high light curtain sensor, survey wide smooth curtain sensor, the long light curtain sensor of survey is connected with signal pickup assembly through the RS232 serial ports with the output terminal of location appearance light curtain sensor; Signal pickup assembly can be plugged in the measurement host, also can be connected with measurement host through serial ports or network interface, the vehicle dimension computing module is installed in measurement host is used to calculate height of car to be measured, vehicle width, length and pose and measurement result is shown through main frame.Height, pose and the width of this light curtain sensor array real-time measuring vehicle in a signal acquisition periods, the length of measuring vehicle when static state.

As shown in Figure 2, the mounting arrangement of light curtain sensor array is: survey high light curtain sensor and comprise an illuminator L1 and the light receiving device S1 corresponding with it, this is surveyed high light curtain sensor and is installed in relatively in the Z axial plane perpendicular to ground; Survey long light curtain sensor and comprise two illuminator L2, L3 and two light receiving device S2s, the S3 corresponding with it, two illuminator L2, L3 and two light receiving device S2, S3 are installed in respectively in the X axial plane that is parallel to ground relatively; Survey wide smooth curtain sensor and comprise two illuminator L4, L5 and two light receiving device S4, S5, two illuminator L4, L5 and two light receiving device S4, S5 are installed in respectively between upper and lower two planes of forming perpendicular to the Z axle and by X axle, Y axle relatively; Location appearance light curtain sensor comprises the wide smooth curtain sensor of survey that two rows are parallel to each other; I.e. four illuminator L4, L5, L6, L7 and four light receiving device S4s corresponding, S5, L6, S7 with it; Every row surveys the installation site of wide smooth curtain sensor: upper edge, the plane X-direction being made up of Y axle, X axle is drawn a center line; Each each one group of light curtain sensor of discharging straggly is parallel along X-direction between two groups of light curtain sensors along front and back, center line both sides; Along Y direction, with the center line be the boundary each other from a distance, form the unglazed curtain zone along X-direction of an elongate in shape.

Light curtain sensor principle is utilized each root infrared ray (ultrared quantity and dense degree are decided by spacing between optical axis quantity of setting and the optical axis) exactly; When measuring vehicle height, width, length; Respectively vehicle is cut into the dozens of measurement plane; Obtain the height of wherein highly the highest level, obtain the width of the wideest plane width of width wherein, obtain plane length that wherein length is the longest length as vehicle as vehicle as vehicle.The fundamental difference that videographic measurment and light curtain are measured is that light curtain measuring method is directly to measure vehicle to be measured, receives the bigger problems of factor affecting such as camera lens sharpness, optimal viewing angle coverage, camera calibration but solved photographing measurement method.Simultaneously, adopt location appearance light curtain sensor can obtain vehicle pose accurately, this vehicle pose is a very crucial parameter, obtains vehicle width and vehicle length accurately through the vehicle pose being carried out the angle of inclination compensation.

A kind of vehicle dimension method for automatic measurement based on the light curtain, as shown in Figure 3, may further comprise the steps:

1, the parking stall measure sensor through burying underground in advance detects whether remain to be surveyed vehicle;

If 2 detect vehicle to be measured, signal picker will trigger light curtain sensor array and start working;

3, when vehicle to be measured gets into light curtain sensor array; In a collection period through surveying high light curtain sensor, location appearance light curtain sensor and surveying the wide corresponding signal of smooth curtain sensor collection and send measurement host to, by measurement host measuring vehicle height, vehicle pose and vehicle width;

Measuring method in the face of height of car, vehicle pose and vehicle width describes respectively down:

(1) height of car measuring method: as shown in Figure 4; When vehicle to be measured gets into when surveying high light curtain sensor scope; To produce shading to surveying high light curtain sensor (illuminator L1 and light receiving device S1), be exactly the height of vehicle to be measured along the be blocked extreme higher position L1_S1_6 (light curtain L1_S1 is the 6th optical axis from bottom to top) of optical axis of Z-direction.

(2) vehicle pose measuring method is like Fig. 5 and shown in Figure 6, when vehicle to be measured passes the plurality of rows light curtain of center line both sides; Can produce the light curtain that vertically passes vehicle body and block; Pick up the car and wore two optical axises that are blocked that two rows survey the edge of wide mechanism, forms a line, this line and tilt angle theta of center line formation as two points; This angle of inclination is referred to as the vehicle pose, and this vehicle pose θ obtains through following calculated with mathematical model:

tagθ＝(H2-H1)/LT1

In the formula: H1 is the distance that center line is ordered to a, and a point is for to be blocked light curtain (the illuminator L4 and the light receiving device S4 of location appearance light curtain sensor) along maximal value on the Y direction; H2 is the distance that center line is ordered to b, and the b point is for to be blocked light curtain (the illuminator L6 and the light receiving device S6 of location appearance light curtain sensor) along maximal value on the Y direction; LT1 is light curtain and the distance of the light curtain between illuminator L6 and the light receiving device S6 between illuminator L4 and the light receiving device S4, and among Fig. 6, θ=θ 1.

(3) vehicle width measuring method: as shown in Figure 7; When vehicle to be measured gets into when surveying wide smooth curtain sensor scope; To produce shading to surveying wide smooth curtain sensor (surveying illuminator L4 and light receiving device S4, illuminator L5 and the light receiving device S5 of wide sensor); If vehicle pose θ is 0, then minimum value L4_S4_6 through the optical axis that is blocked along Y direction (light curtain L4_S4 from the centre the 6th optical axis) left and maximal value L5_S5_6 (light curtain L5_S5 from the centre the 6th optical axis) to the right can calculate the width of vehicle; If vehicle pose θ is not 0, and is as shown in Figure 8, then vehicle width is carried out the angle of inclination compensation, thereby obtain vehicle width to be measured accurately according to vehicle pose θ, the computation model of vehicle width W (LT3 among the figure) is:

W＝cosθ*LT4

Wherein, θ is vehicle pose (angle of inclination), and the length value of LT4 equals the distance between a, the d, and a, d are the be blocked maximal value L4_S4_6 of optical axis of the minimum value L5_S5_6 of the optical axis that is blocked along Y direction light curtain and light curtain, and θ=θ 2.

4, when vehicle to be measured remains static and fall into the light curtain zone of measuring vehicle length, survey long light curtain sensor acquired signal and send measurement host to, carry out measuring vehicle length by measurement host.

Vehicle length measurement method: as shown in Figure 9; When vehicle get into to be surveyed long light curtain sensor scope; To produce shading to surveying long light curtain sensor (the illuminator L2 of the long light curtain sensor of side and light receiving device S2, illuminator L3 and light receiving device S3); If vehicle pose θ is 0, then minimum value L2_S2_7 through the optical axis that is blocked along X-direction (light curtain L2_S2 from the centre the 7th optical axis) left and maximal value L3_S3_8 (light curtain L3_S3 from the centre the 8th optical axis) to the right can calculate the length of vehicle; If vehicle pose θ is not 0, and is shown in figure 10, then vehicle length carried out the angle of inclination compensation, thereby obtain vehicle width accurately according to vehicle pose θ.The computation model of vehicle length L T is:

LT＝ST2/cosθ

In the formula; ST2=ST-ST1; The ST value equals along the distance between X-direction a, the b; A is the minimum value along X-direction light curtain (illuminator L4 and light receiving device S4) or (illuminator L5 and light receiving device S5), and b is the maximal value along X-direction light curtain (illuminator L6 and light receiving device S6) or (illuminator L7 and light receiving device S7);

ST1=sin θ * W, W is a vehicle width.

Through above-mentioned steps, can realize height of car, vehicle width and length are realized accurate measurement function.

It is emphasized that; Embodiment of the present invention is illustrative; Rather than it is determinate; Therefore the present invention is not limited to the embodiment described in the embodiment, and every other embodiments that drawn by those skilled in the art's technical scheme according to the present invention belong to the scope that the present invention protects equally.

Claims (9)

1. vehicle dimension automatic measurement system based on the light curtain; It is characterized in that: connect and compose by measurement host, signal pickup assembly and light curtain sensor array; Described smooth curtain sensor array is the spatial structure that is made up of the high light curtain sensor of survey, the wide smooth curtain sensor of survey, the long light curtain sensor of survey; The output terminal of surveying high light curtain sensor, the wide smooth curtain sensor of survey, the long light curtain sensor of survey is connected with signal pickup assembly, calculates height of car to be measured, vehicle width, length behind the detection signal that measurement host reception light curtain sensor array transmits.

2. the vehicle dimension automatic measurement system based on the light curtain according to claim 1; It is characterized in that: the high light curtain sensor of described survey comprises an illuminator L1 and the light receiving device S1 corresponding with it, and this is surveyed high light curtain sensor and is installed in relatively in the Z axial plane perpendicular to ground; The long light curtain sensor of described survey comprises two illuminator L2, L3 and two light receiving device S2s, the S3 corresponding with it, and two illuminator L2, L3 and two light receiving device S2, S3 are installed in respectively in the X axial plane that is parallel to ground relatively; The wide smooth curtain sensor of described survey comprises two illuminator L4, L5 and two light receiving device S4, S5, and two illuminator L4, L5 and two light receiving device S4, S5 are installed in respectively between upper and lower two planes of forming perpendicular to the Z axle and by X axle, Y axle relatively.

3. the vehicle dimension automatic measurement system based on the light curtain according to claim 1 and 2; It is characterized in that: described smooth curtain sensor array also comprises a location appearance light curtain sensor; This location appearance light curtain sensor comprises the wide smooth curtain sensor of survey that two rows are parallel to each other; The installation site that every row surveys wide smooth curtain sensor is: upper edge, the plane X-direction being made up of Y axle, X axle is drawn a center line; Each each one group of light curtain sensor of discharging straggly is parallel along X-direction between two groups of light curtain sensors along front and back, center line both sides; Along Y direction, with the center line be the boundary each other from a distance, form the unglazed curtain zone along X-direction of an elongate in shape.

4. the vehicle dimension automatic measurement system based on the light curtain according to claim 3 is characterized in that: described signal pickup assembly is plugged in the measurement host and through serial ports with built-in method and is connected with the high light curtain sensor of survey, the wide smooth curtain sensor of survey, the long light curtain sensor of survey and location appearance light curtain sensor.

5. the vehicle dimension automatic measurement system based on the light curtain according to claim 3 is characterized in that: described signal pickup assembly is connected with measurement host through serial ports or network interface with external method and is connected with the high light curtain sensor of survey, the wide smooth curtain sensor of survey, the long light curtain sensor of survey and location appearance light curtain sensor through serial ports.

6. the vehicle dimension automatic measurement system based on the light curtain according to claim 1 and 2 is characterized in that: described measurement host also is connected to be used to detect whether remain to be surveyed the work of vehicle with the control signal collector with a parking stall measure sensor.

7. according to the measuring method of each said system of claim 1 to 6, it is characterized in that: may further comprise the steps:

Step 1:, detect whether remain to be surveyed vehicle through the parking stall measure sensor of burying underground in advance;

Step 2: if detect vehicle to be measured, signal picker will trigger light curtain sensor array and start working;

Step 3: when vehicle to be measured gets into light curtain sensor array; In a collection period through surveying high light curtain sensor, location appearance light curtain sensor and surveying the wide corresponding signal of smooth curtain sensor collection and send measurement host to, by measurement host measuring vehicle height, vehicle pose and vehicle width;

Step 4: when vehicle to be measured remains static and fall into the light curtain zone of measuring vehicle length, survey long light curtain sensor acquired signal and send measurement host to, carry out measuring vehicle length by measurement host.

8. based on the described vehicle dimension method for automatic measurement of claim 7 based on the light curtain; It is characterized in that: the method for measuring vehicle height is in the said step 3: when vehicle to be measured gets into when surveying high light curtain sensor scope, along the be blocked extreme higher position of optical axis of Z-direction;

The measuring vehicle pose obtains through following calculated with mathematical model in the said step 3:

tagθ＝(H2-H1)/LT1

In the formula: θ is the vehicle pose, and H1 is the distance that center line is ordered to a, and a point is that a location appearance light curtain sensor light curtain is along maximal value on the Y direction; H2 is the distance that center line is ordered to b, and the b point is that another location appearance light curtain sensor is along maximal value on the Y direction; LT1 is the distance of two location appearance light curtain sensors;

The measuring vehicle width W obtains through following computation model in the said step 3:

W＝cosθ*LT4

Wherein, θ is the vehicle pose, and the length value of LT4 equals the distance between a, the d, and a, d are the be blocked maximal value of optical axis of the minimum value of the optical axis that is blocked along Y direction light curtain and light curtain.

9. the vehicle dimension method for automatic measurement based on the light curtain according to claim 7 is characterized in that: measuring vehicle length L T adopts following calculated with mathematical model to obtain in the said step 4:

LT＝ST2/cosθ

In the formula, ST2=ST-ST1, the ST value equals along the distance between X-direction a, the b, and a is the minimum value along X-direction light curtain, and b is the maximal value along X-direction light curtain;

ST1=sin θ * W, W is a vehicle width.

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