CN116124393A - Bridge multipoint dynamic deflection measuring method and device during off-axis measurement - Google Patents
Bridge multipoint dynamic deflection measuring method and device during off-axis measurement Download PDFInfo
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Abstract
The invention relates to the technical field of bridge structure health monitoring by a visual sensing technology, and discloses a bridge multipoint dynamic deflection measuring method and device during off-axis measurement.
Description
Technical Field
The invention relates to the technical field of bridge structure health monitoring by a visual sensing technology, in particular to a bridge multipoint dynamic deflection measuring method and device during off-axis measurement.
Background
The visual sensing technology obtains structural displacement video through image acquisition equipment such as an industrial camera and a digital camera, obtains pixel displacement of a structure through algorithms such as template matching, and then realizes conversion from pixel distance to actual distance through a scale factor to obtain actual displacement of the structure. Compared with the measurement by using equipment such as an acceleration sensor, a microwave radar, a laser radar and the like, the vision sensing technology is low in measurement cost, and can realize multi-point dynamic monitoring, so that the vision sensing technology is widely paid attention to domestic and foreign scholars.
However, in practical engineering, a complex field environment around a bridge brings a lot of problems, so that parallel shooting of the bridge is difficult to realize, at this time, a horizontal angle and a pitch angle exist between an imaging plane of a camera and an object plane (such working condition is called off-axis measurement), which can cause different scale factors of each measurement point of a structure on an image, when the multi-point dynamic deflection of the bridge is measured, the traditional method needs to measure the object distance and the camera angle of each point when calculating the multi-point scale factors, and the traditional method combines internal parameters of the camera to calculate, or calculates through targets with known actual sizes which are pre-arranged at each measurement point, so that the process is complicated.
In view of this, how to calculate the bridge multipoint scaling factor under the off-axis condition more rapidly and accurately is a problem to be solved in the technical field.
Disclosure of Invention
The technical problem to be solved by the invention is that in the process of measuring the multi-point dynamic deflection of the bridge under the off-axis measurement condition, the traditional method is used for calculating the multi-point scaling factor, so that the object distance of each point is required to be measured, or the object distance is calculated through targets with known actual sizes which are arranged at each measuring point in advance, and the process is complicated.
The invention adopts the following technical scheme:
in a first aspect, the invention provides a method for measuring bridge multipoint dynamic deflection during off-axis measurement, comprising the following steps:
shooting bridge vibration videos under the off-axis measurement condition, and reading a camera horizontal angle and a camera pitch angle through a camera;
selecting a plurality of measuring points according to the bridge vibration video, selecting an interested region of each measuring point, and extracting pixel displacement of the plurality of measuring points from the bridge vibration video by using a matching algorithm;
after the actual size of the object plane of the first feature is obtained, calculating to obtain a central point scale factor of the first feature;
calculating to obtain the object distance between the camera and the central point of the first feature of the measured object plane by combining the image coordinates of the central point of the first feature and the corresponding central point scale factors of the central point with the camera horizontal angle, the camera pitch angle and the camera internal parameters;
calculating all measuring point scale factors by combining the object distance of the first characteristic of the object plane of the camera with the camera horizontal angle, the camera pitch angle and the camera internal parameters;
and calculating to obtain the actual physical displacement of the corresponding measuring point according to the scale factors of all the measuring points and the pixel displacement of the plurality of measuring points.
Preferably, the extracting the pixel displacement of a plurality of measuring points in the bridge vibration video by using a matching algorithm specifically includes:
H 2 ,L 2 ＝maxIndex(SI)；
wherein n11 is the width dimension of the previous frame time image, n12 is the height dimension of the previous frame time image, i is the width position of the convolution template after zero padding, and j is the height position of the convolution template after zero padding; i 1 (x, y) is the pixel value of the previous frame moment image at the x, y position, I 2 (i+x, j+y) is the pixel value of the image at the i+x, j+y position at the next frame time; h 1 And H is 2 The positions of the matching characteristic points corresponding to the previous frame and the following frame in height are respectively L 1 And L is equal to 2 The positions of the matching feature points corresponding to the front frame and the rear frame in the width direction are respectively calculated, the total number of the positions of the m1 matching feature points in the height direction is calculated, the total number of the positions of the m2 matching feature points in the width direction is calculated, delta H is the calculated vibration displacement between the front frame and the rear frame, and delta L is the calculated horizontal displacement between the front frame and the rear frame.
Preferably, the central point scale factor of the first feature is the scale factor SF of the image point corresponding to the actual object plane size of the first feature First one The center point scale factor SF of the first feature First one The calculation formula is as follows:
d known is the actual size of the object plane; i known The corresponding pixel length on the image is the known physical object plane dimension.
Preferably, the object distance D between the camera and the center point of the first feature of the object plane is calculated by combining the camera horizontal angle, the camera pitch angle and the camera internal reference through the image coordinates of the center point of the first feature and the corresponding center point scale factors, specifically:
wherein:
SF first one A scale factor that is a first feature; (x) 0 ,y 0 ) The center point image coordinates of the first feature; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ,y c ) The coordinates of the optical center point of the camera; alpha is the camera pitch angle; beta is the camera horizontal angle.
Preferably, the object distance between the camera and the first feature of the object plane is measured, and the camera horizontal angle, the camera pitch angle and the camera internal reference are combined to calculate and obtain the scale factors SF of all measuring points i The method specifically comprises the following steps:
wherein:
d is the object distance of the first feature; (x) 0 ,y 0 ) The image coordinates of the object distance point are measured for the image coordinates of the central point of the first feature or directly; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ,y c ) Imaging coordinates for a camera photo-center point; (x) i ,y i ) For waiting for SF i Is defined by the image coordinates of (a); alpha is the camera pitch angle;beta is the camera horizontal angle.
Preferably, the obtaining the actual object plane dimension of the first feature specifically includes:
according to the form and actual size of each component which is imported in the database and forms the bridge;
obtaining an alternative target object matched with each corresponding component in the form in the video frame through image matching;
synchronously analyzing the pixel displacement of the identified candidate target object while analyzing the pixel displacement of a plurality of measuring points in the bridge vibration video;
and screening one of the candidate target objects, the pixel displacement of which meets the preset condition, from the candidate target objects to serve as the first characteristic, and taking the actual size of the corresponding screened candidate target object as the actual size of the object plane of the first characteristic.
Preferably, the preset conditions specifically include:
taking the average pixel displacement of each measuring point as a reference, wherein the pixel displacement of the alternative target object is less than 50% of the average pixel displacement+10% and less than 70% of the minimum pixel displacement in the measurement point+10％。
Preferably, after obtaining the pixel displacement of the plurality of measuring points, the selecting of the first feature specifically includes:
screening one or more pairs of measuring points, of which the corresponding measuring points are adjacent in space positions, the corresponding pixel displacement directions are opposite in video frames, and the pixel displacement difference of the two is smaller than a preset value;
extracting a bridge component positioned between the two measuring points according to the one or more pairs of the screened measuring points;
searching the actual size of the bridge assembly in a database in an image matching mode; if so, taking the corresponding bridge component as a first characteristic; if none of the bridge components is found, the bridge component which is the easiest to measure manually is selected as the first characteristic, and the physical dimension measurement is carried out by staff.
Preferably, the preset value is obtained by taking the resolution of the camera and the distance between the camera and the bridge as weighted values and weighting the minimum pixel displacement of the measuring point.
In a second aspect, the present invention further provides a bridge multi-point dynamic deflection measurement device during off-axis measurement, for implementing the bridge multi-point dynamic deflection measurement method during off-axis measurement in the first aspect, where the device includes:
at least one processor; and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor for performing the method of off-axis measurement bridge multi-point dynamic deflection measurement of the first aspect.
In a third aspect, the present invention also provides a non-volatile computer storage medium storing computer executable instructions for execution by one or more processors to perform a method of bridge multipoint dynamic deflection measurement when measured off-axis according to the first aspect.
In the bridge multipoint dynamic deflection measurement process, the calculation of the multipoint scale factors only needs to measure the object distance at any point of the object plane or the actual size of any feature of the object plane, and the scale factors of all measuring points can be calculated by combining the camera angle, including the camera horizontal angle and the camera pitch angle, and the camera internal parameters, including the camera focal length, the image coordinates of the optical center point and the pixel size, so that the conversion from pixel displacement to actual displacement is realized. The method provided by the embodiment of the invention has the advantages of simple calculation and convenient application, and can rapidly and accurately calculate the dynamic deflection change of a plurality of measuring points of the bridge.
Drawings
In order to more clearly illustrate the technical solution of the embodiments of the present invention, the drawings that are required to be used in the embodiments of the present invention will be briefly described below. It is obvious that the drawings described below are only some embodiments of the present invention, and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a schematic diagram of an off-axis measurement provided by an embodiment of the present invention;
FIG. 2 is a schematic diagram of a y-axis direction of a calculation model of an off-axis measurement scale factor when only a pitch angle exists according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an x-axis direction of a calculation model of an off-axis measurement scale factor when only a pitch angle exists according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of an x-axis direction of a calculation model of an off-axis measurement scale factor when a horizontal angle and a pitch angle are both present in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram of an x-axis direction of an off-axis measurement center point object distance calculation model when a horizontal angle and a pitch angle are both present in the embodiment of the present invention;
FIG. 6 is a schematic diagram of a y-axis direction of an off-axis measurement center point object distance calculation model when a horizontal angle and a pitch angle exist simultaneously;
FIG. 7 is a schematic flow chart of a method for measuring multi-point dynamic deflection of a bridge during off-axis measurement according to an embodiment of the present invention;
FIG. 8 is a schematic flow chart of a method for measuring bridge multipoint dynamic deflection during off-axis measurement according to an embodiment of the present invention;
FIG. 9 is another schematic flow chart of obtaining a first feature in a method for measuring multi-point dynamic deflection of a bridge during off-axis measurement according to an embodiment of the present invention;
fig. 10 is a graph showing the image scale factor SF plotted with x-coordinate for y=540 pixel under a given condition in the first embodiment of the present invention;
FIG. 11 is a schematic illustration of target paper adhesion and 5.75cm by 5.75cm square target numbering for a verification experiment in accordance with an embodiment of the present invention;
FIG. 12 shows the camera angle and focal length parameters for twelve conditions in one example of a verification experiment;
FIG. 13 is a flowchart of a method for calculating a multipoint scale factor during off-axis measurement in a verification experiment according to an embodiment of the present invention;
FIG. 14 is a flow chart of measuring multi-point dynamic deflection of a bridge structure according to an embodiment of the present invention;
fig. 15 is a vibration-captured image of a half-span truss bridge according to an embodiment of the present invention;
FIG. 16 is a schematic diagram of a node to be analyzed according to an embodiment of the present invention;
FIG. 17 is a comparative schematic diagram of vibration measurement of nodes 1-6 according to an embodiment of the present invention;
FIG. 18 is a standard deviation calculation result of a displacement estimation deviation according to an embodiment of the present invention;
fig. 19 is a schematic structural diagram of a bridge multipoint dynamic deflection measuring device during off-axis measurement according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In the description of the present invention, the terms "inner", "outer", "longitudinal", "transverse", "upper", "lower", "top", "bottom", etc. refer to an orientation or positional relationship based on that shown in the drawings, only for convenience in describing the present invention, and do not require that the present invention must be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
Before the technical scheme of the embodiment of the invention is described, the theoretical basis of the calculation of the multipoint scale factors in the bridge multipoint dynamic deflection measuring method during off-axis measurement is described from the theoretical point of a basic model. In the embodiment of the present invention, the first feature is specifically expressed as that any point on the image corresponds to a corresponding position point on the object surface, for example, the point P1 on the image corresponds to the point P1 on the object surface.
Referring to fig. 1, first, when only a pitch angle exists, the y-axis direction diagram of the off-axis measurement scale factor calculation model is shown in fig. 2 and the x-axis direction diagram is shown in fig. 3, and at this time, the known amounts are: image center point (optical center) coordinates p (x) c ,y c ) Camera focal length f, pixel size l ps Camera elevation angle alpha, optical center point object distance D 0 。
In fig. 2: p (x) c ,y c ) Is the center point (optical center) of the image, P is the position of the object surface corresponding to the center point (optical center) of the image, op is the focal length f, P1 (x) c ,y 1 ) And p2 (x) c ,y 2 ) In the direction perpendicular to the camera optical center p (see FIG. 2, where y at p1, the x coordinate is unchanged 1 >y c Y at p2 2 <y c ) The upper two points, α, are elevation angles.
For point p1, we get from similar triangles:
so that:
then by the sine theorem:
so that:
namely, the scale factor SF is:
wherein:
the p2 point is calculated by the same method:
namely, the scale factor SF is:
wherein:
thus passing through any point (x) c ,y i ) Scaling factor:
then expanding to the calculation of the scale factor of any point on the image when only the pitch angle exists, the calculation principle of the formula (1) is known, and only the (x) i ,y c ) The distance from the point to the optical center O is equal to (x) i ,y c ) The object distance of the point can be calculated to be x in the abscissa of the image coordinate system i Thus, as shown in FIG. 3, the object distance D is measured by the known focal length f of the camera and the optical center point 0 Derived from isoparametric parameters (x) i ,y c ) The distance from the point to the optical center O is equal to (x) i ,y c ) Substituting the object distance of the point into the formula (1) to obtain any point (x) of the image only with the pitch angle i ,y i ) The scale factor formula:
in fig. 3: p (x) c ,y c ) Is the center point (optical center) of the image, P is the position of the object surface corresponding to the center point (optical center), and Op is the focal length of the cameraf，q1(x 1 ,y c ) And q2 (x) 2 ,y c ) In the horizontal direction of the camera optical center p (refer to fig. 1, the y coordinate is unchanged, wherein x is at q 1) 1 <x c X at q2 2 >x c ) Two points above.
At this time:
so that:
back focal length change:
at this time, the reference point and the optical center after the change are substituted into the formula (1) to obtain any point (x i ,y i ) The scale factor formula:
wherein:
next consider that any point (x i ,y i ) The scale factor is calculated, and at this time, the horizontal angle does not affect the derivation process of the formula (1) but only (x) i ,y c ) The distance from the point to the optical center O is equal to (x) i ,y c ) Calculation of object distance of points, therefore, deduction is performed by referring to the calculation principle of the formula (2), and a calculation model is shown in fig. 4:
at this time, the known amounts are: image center point (optical center) coordinates (x c ,y c ) Camera focal length f, pixel size l ps Camera elevation angle alpha, camera horizontal angle beta, optical center point object distance D 0 。
In fig. 4: op=f, op=d 0 ，q1(x 1 ,y c ),q2(x 2 ,y c ) Is smaller and larger than x in the x-axis coordinate 0 Point, β is camera horizontal angle:
at this time:
at this time
By sine theorem:
so that:
D 1 ＝OQ1＝OA-AQ1；
and (3) the same principle:
so that:
D 2 ＝OQ2＝OB+BQ2；
at the moment, substituting the changed reference point and the optical center into the formula (1) to obtain any point (x when the horizontal pitch angle and the pitch angle exist simultaneously i ,y i ) The scale factor formula:
simplifying and obtaining:
wherein:
the above scale factor calculation formula is known as: image center point (optical center) coordinates (x c ，y c ) Camera focal length f, pixel size l ps Camera elevation angle alpha, camera horizontal angle beta, optical center point object distance D 0 . Further spreading to a calculation formula of a scale factor when the object distance D of any point is known, wherein the object distance D of the optical center point is obtained only by calculating the object distance D of any point when the horizontal angle and the pitch angle exist simultaneously 0 Will be D 0 The expression is brought into the formula (3) to obtain a calculation formula of the scale factor when the object distance of any point is known, and the deduction process is as follows:
first calculate and select point p 0 (x 0 ，y 0 ) The y-axis coordinates of the same point p 1 (x c ，y 0 ) Point object distance D 1 The calculation model is shown in fig. 5, and the known quantity is: image center point (optical center) coordinates (x c ，y c ) Camera focal length f, pixel size l ps Camera elevation angle alpha, camera horizontal angle beta, arbitrary point p 0 Object distance D:
in fig. 5: the p01 and p02 coordinates are (x 0 ，y 0 ) Refer to p 0 (x 0 ，y 0 ) Point x coordinate is largeAt the sum of less Yu Guangxin points p (x c ，y c ) A situation;
p1p01＝(x c -x 0 )*l ps ，p2p01＝(x c -x 0 )*l ps ；
OP01＝D；OP02＝D；
from similar triangles:
the method comprises the following steps:
beta is the horizontal angle:
P1P01′＝P01P01′*tanβ；
P2P02′＝P02P02′*tanβ；
thus:
OP01＝OP01′+P1P01′；
OP02＝OP02′-P2P02′；
then:
further from p 1 (x c ，y 0 ) Point object distance D 1 Calculate the optical center point p (x) c ，y c ) Point object distance D 0 The calculation model is shown in fig. 6:
in FIG. 6, the coordinates p1 and p2 are (x) c ，y 0 ) Refer to p 0 (x 0 ，y 0 ) The point y coordinate is greater than less than Yu Guangxin point p (x c ，y c )，Op＝f；
pp1＝(y c -y 0 )*l ps ，pp2＝(y c -y 0 )*l ps ；
OP01＝D 1 ，OP02＝D 1 ；
From similar triangles:
the method comprises the following steps:
alpha is the pitch angle:
PP1′＝P1P1′*tanα；
PP2′＝P2P2′*tanα；
thus:
OP＝OP1′-PP1′；
OP＝OP2′+PP2′；
then:
wherein:
at this time, the formula (5) is brought into the formula (3) to obtain a calculation formula of the scale factor when the object distance at any point is known:
wherein:
d is the object distance at any known point (the object distance of the first feature if the actual size of the first feature is measured); (x) 0 ,y 0 ) Imaging coordinates for a known object distance point; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ,y c ) The coordinates of the optical center point of the camera; (x) i ,y i ) Image coordinates for SF points to be solved; alpha is the camera pitch angle; beta is the camera horizontal angle.
Next, deriving a calculation formula of the object distance of the known scaling factor point in off-axis measurement from the formula (6), and only moving the object distance D of any point to the left of the formula, wherein the calculation formula is as follows:
wherein:
SF is a known feature center point scale factor; (x) 0 ,y 0 ) Image coordinates for a known object distance center point; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ,y c ) The coordinates of the optical center point of the camera; alpha is the camera pitch angle; beta is the camera horizontal angle.
Therefore, the scale factor of any point of the object plane can be obtained only by calculating the actual size of any point of the object distance or any feature of the object plane, the camera angle and the internal reference information through the formula.
Example 1:
the embodiment of the invention provides a bridge multipoint dynamic deflection measuring method during off-axis measurement, which is shown in fig. 7 and comprises the following steps:
in step 201, bridge vibration video is photographed under off-axis measurement conditions, and camera horizontal angle and camera pitch angle are read by a camera.
In step 202, a plurality of measuring points are selected according to the bridge vibration video, an interested region of each measuring point is selected, and pixel displacement of the plurality of measuring points is extracted from the bridge vibration video by using a matching algorithm.
In step 203, after the actual object plane size of the first feature is obtained, a central point scale factor of the first feature is calculated.
In step 204, the object distance between the camera and the center point of the first feature of the object plane is calculated by combining the camera horizontal angle, the camera pitch angle and the camera internal reference through the image coordinates of the center point of the first feature and the corresponding center point scale factors.
In step 205, the object distance between the camera and the first feature of the object plane is measured, and the camera horizontal angle, the camera pitch angle and the camera internal parameters are combined to calculate and obtain the scale factors of all measuring points.
In step 206, according to the scale factors of all the measuring points and the pixel displacements of the measuring points, the actual physical displacements of the corresponding measuring points are calculated.
In the bridge multipoint dynamic deflection measurement process, the calculation of the multipoint scale factors only needs to measure the object distance of any point of the object plane or the actual size of any feature of the object plane, and the scale factors of all measuring points can be calculated by combining the camera angles, including the camera horizontal angle, the camera pitch angle, the camera internal parameters, including the camera focal length, the image coordinates of the optical center point and the pixel size, so that the conversion from pixel displacement to actual displacement is realized. The method provided by the embodiment of the invention has the advantages of simple calculation and convenient application, and can rapidly and accurately calculate the dynamic deflection change of a plurality of measuring points of the bridge.
In the embodiment of the invention, a specific implementation process is provided for extracting the pixel displacement of a plurality of measuring points in the bridge vibration video by using a matching algorithm, and the specific implementation process comprises the following steps:
H 2 ,L 2 ＝maxIndex(SI)；
wherein n11 is the width dimension of the previous frame time image, n12 is the height dimension of the previous frame time image, i is the width position of the convolution template after zero padding, and j is the height position of the convolution template after zero padding; i 1 (x, y) is the pixel value of the previous frame moment image at the x, y position, I 2 (i+x, j+y) is the pixel value of the image at the i+x, j+y position at the next frame time; h 1 And H is 2 The positions of the matching characteristic points corresponding to the previous frame and the following frame in height are respectively L 1 And L is equal to 2 The positions of the matching feature points corresponding to the front frame and the rear frame in the width direction are respectively calculated, the total number of the positions of the m1 matching feature points in the height direction is calculated, the total number of the positions of the m2 matching feature points in the width direction is calculated, delta H is the calculated vibration displacement between the front frame and the rear frame, and delta L is the calculated horizontal displacement between the front frame and the rear frame.
In the embodiment of the invention, the image of the convolution template after zero padding is used for ensuring that the image size of the region of interest before and after convolution is unchanged, and the same convolution is adopted, and the previous frame image serving as the convolution template is subjected to four-side zero padding so that the dimension of the convolution result is consistent with the original image size. The specific convolution templates and means are well-established prior art supports and are not described in any great detail herein.
In the embodiment of the present invention, the central point scaling factor of the first feature is the scaling factor SF of the image point corresponding to the actual object plane size of the first feature First one Providing a center point scale factor SF of the first feature First one The calculation formula is as follows:
d known is the actual size of the object plane; i known The corresponding pixel length on the image is the known physical object plane dimension.
In the embodiment of the present invention, the object distance D between the center point of the first feature of the camera and the measured object plane is calculated by combining the image coordinates of the center point of the first feature and the corresponding scale factors of the center point, the camera horizontal angle, the camera pitch angle and the camera internal reference, and the specific implementation is provided as follows:
wherein:
SF first one A scale factor that is a first feature; (x) 0 ,y 0 ) The center point image coordinates of the first feature; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ,y c ) The coordinates of the optical center point of the camera; alpha is the camera pitch angle; beta is the camera horizontal angle.
In the embodiment of the invention, the object distance of the first characteristic of the object plane is measured by the camera, and the camera horizontal angle, the camera pitch angle and the camera internal reference are combined to calculate and obtain the scale factors SF of all measuring points i The method specifically comprises the following steps:
wherein:
d is the object distance of the first feature; (x) 0 ,y 0 ) The image coordinates of the object distance point are measured for the image coordinates of the central point of the first feature or directly; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ,y c ) Imaging coordinates for a camera photo-center point; (x) i ,y i ) For waiting for SF i Image sitting of (a)Marking; alpha is the camera pitch angle; beta is the camera horizontal angle.
As shown in fig. 8, in combination with the embodiment of the present invention, a preferred implementation solution is provided for obtaining the actual size of the object plane of the first feature, which specifically includes:
in step 301, the morphology and actual dimensions of the various components making up the bridge are imported from the database.
In step 302, candidate target objects in the video frame that are morphologically matched to the respective components are obtained by image matching.
In step 303, the pixel displacements of the identified candidate target object are analyzed synchronously while the pixel displacements of the plurality of measurement points are extracted from the bridge vibration video are analyzed.
In step 304, one of the candidate target objects whose pixel displacement satisfies a preset condition is selected as the first feature, and the actual size of the candidate target object that is selected correspondingly is selected as the object plane actual size of the first feature.
The preset conditions specifically include: taking the average pixel displacement of each measuring point as a reference, the pixel displacement of the alternative target object is less than 50% ± 10% of the average pixel displacement and less than 70% ± 10% of the minimum pixel displacement in the measuring point.
In addition to the above-mentioned selection manners of the first feature provided in step 301-step 304, the embodiment of the present invention provides another alternative manner, as shown in fig. 9, of selecting the first feature after obtaining the pixel displacement of the plurality of measurement points, which specifically includes:
in step 401, the corresponding measuring points are screened to be adjacent in space position, the corresponding pixel displacement directions are opposite in the video frame, and the pixel displacement difference between the two is smaller than one or more pairs of measuring points of a preset value.
In step 402, a bridge module is extracted from the one or more pairs of points that are screened to be located intermediate the two points.
In step 403, the actual size of the bridge module is searched in the database by means of image matching.
In step 404, if found, the corresponding bridge module is used as the first feature.
If none of the bridge components is found, the bridge component that is the most easily measured manually is selected as the first feature and the physical dimension measurement is performed by the staff 405.
The preset value is obtained by taking the resolution of the camera and the distance between the camera and the bridge as weighted values and weighting the minimum pixel displacement of the measuring point. Wherein, the larger the resolution of the camera is, the smaller the associated weighting value is, and the larger the distance between the camera and the bridge is, the larger the associated weighting value is; in a preferred embodiment, the weighting values associated with the resolution of the camera and the distance of the camera from the bridge are independent of each other. The parameter values to be used are empirically set according to actual conditions, and are not further limited herein.
In addition, in actual engineering, the bridge structure has the characteristics of long span and small thickness, meanwhile, most of the lower part of the bridge is traffic flow, ravines and water flow, the horizontal angle between the object plane and the image plane is unavoidable when the bridge vibration video shooting is carried out, the traditional method only utilizes pitch angle information when the scale factor calculation is carried out, multiple object distance measurement or target distribution is needed for calculation, the operation is complicated, the measurement is difficult, and the method provided by the invention fully utilizes the pitch angle and the horizontal angle information, and the scale factors of all points on the bridge can be calculated only by measuring the actual size of any feature or the object distance of any point on the bridge, so the operation is simple, the realization is convenient, and the method is more suitable for the bridge structure.
In addition, in the invention, the scale factor used in the process of converting the bridge vertical pixel displacement extracted by the template matching algorithm into the actual displacement is calculated by the measuring point at the first frame position of the bridge vibration video. At the moment, error analysis is carried out given an initial quantity, the object distance of a center point is set to be D=9000 mm, the bridge vibration video size is 1920x1080, the focal length f=35 mm of a camera, and the pixel size is l ps =0.0048 mm, the optical center position is (x c ,y c ) = (960,540), camera elevation angle α=30°, camera horizontal angle β=60°, and multiple points of the bridge are distributedThe center positions of the images are respectively (x) 1 ,y 1 )＝(100,540)，(x 2 ,y 2 )＝(300,540)，(x 3 ,y 3 )＝(500,540)，(x 4 ,y 4 )＝(700,540)，(x 5 ,y 5 ) In general, the bridge has small vertical vibration, assuming that the vibration amplitude is ±5 pixels, and drawing a curve of change of SF with x coordinates when y=540 pixels under given conditions, as shown in fig. 10, the result is that SF changes monotonically with x coordinates, so that when the vibration amplitude is ±5 pixels, the error is the largest at ±5 pixels, and the calculation result is as follows:
the points one to five in the table represent (x) 1 ,y 1 )-(x 5 ,y 5 )，SF Measuring point SF is the measurement point position scale factor calculated under given conditions +5pixel With SF -5pixel The relative error of the scale factors at the measuring point + -5 pixel and the scale factors at the measuring point + -5 pixel, err1 and err2 are calculated as follows:
the result shows that the scale factor at the measuring point + -5 pixel has a small difference from the scale factor at the measuring point, so that for measuring the multi-point vertical dynamic deflection of the bridge, the scale factor of the measuring point is feasible to calculate by using the first frame position of the bridge vibration video, and meanwhile, in order to verify the accuracy of the calculation result of the formula, the invention is also verified through the design experiment of the embodiment 2.
Example 2:
the embodiment of the invention provides an experiment, and the simulated bridge structure of the experiment comprises the following steps:
four pieces of target paper are stuck on the positions, parallel to the x axis, of the object plane, 3 square targets with the same size and 5.75cm multiplied by 5.75cm are arranged on each piece of target paper, 12 square targets are numbered in sequence from left to right, the target paper sticking schematic diagram and the square target numbers are shown in fig. 11, shooting is respectively carried out at different angles, twelve working condition settings are shown in fig. 12, meanwhile, due to inaccurate object distance measurement, the object distance of the center point of each target is calculated by adopting a formula (7) in an experiment, as shown in fig. 13, the experimental flow is as follows:
in step 501, a picture of a different angle is taken by changing the camera position.
In step 502, four corner points of each target are clicked for multiple times, and the central point SFreal of each target is calculated as a reference value according to a scale factor calculation formula when the actual size of the object plane is known.
In step 503, each target center point object distance Di is calculated by equation (7).
In step 504, all remaining target center points SF are calculated from one of the target center point object distances Di, compared to SFreal, and the error calculated.
The test results are shown in the following table 1:
the first column in table 1 shows different conditions, the third column "known" shows that the target center point object distance is a known amount, and all the remaining target center point scale factors are calculated; the "SFreal" row represents each target center point scaling factor calculated from a scaling factor calculation formula for a known object plane actual size by square target size, the "SF" row represents each target center point scaling factor calculated from a full-field scaling factor calculation formula (6) for off-axis measurement of a target center point object distance in the third column, and the "err" row represents the relative error between the SFreal and SF values as calculated by the following formula:
the test result shows that the scale factor calculated by the method is similar to the scale factor calculated by the target size, the relative error is less than or equal to 3%, the precision meets the measurement requirement, and meanwhile, compared with the traditional method, the method provided by the embodiment of the invention can obtain the multipoint scale factor by measuring the object distance for multiple times and calculating, and is time-saving and labor-saving.
Example 3:
the embodiment 1 of the invention provides a specific application embodiment of a bridge multipoint dynamic deflection measuring method during off-axis measurement, which is used for showing the application of the method in the vibration measuring process.
The flow chart of the structural vibration measurement based on the visual sensing technology is shown in fig. 14, a structural multipoint measurement region of interest (Region of Interest, abbreviated as ROI) is firstly extracted, then a template matching method is used for obtaining bridge structural multipoint pixel displacement extraction based on the region of interest, then a multipoint scale factor is calculated, and finally the structural multipoint pixel displacement is converted into an actual displacement vibration time interval signal through the corresponding scale factor, so that the bridge multipoint dynamic deflection change is obtained. The method provided by the invention utilizes the formula (6) to calculate the multipoint scale factor, and realizes the conversion from pixel displacement to actual displacement.
The vibration measurement of the half-span truss bridge is taken as an example, and the application of the method provided by the invention in the multi-point dynamic deflection measurement of the bridge is described below.
The method comprises the steps of hinging two ends of a truss bridge with the span 0.3937 multiplied by 14=5.6m, the section height of the truss bridge is 0.4m, the transverse width of the truss bridge is 0.3937m, vibration excitation is applied to the truss bridge through a vibrating table, then an industrial camera is used for shooting a half-span bridge structure vibration video of the truss bridge structure vibration video at an angle which is not parallel to the truss plane, one frame of vibration image in the obtained video is as shown in fig. 15, the video frame rate is 120fps, the image is 1920 multiplied by 1080, the structural feature part is selected to be a truss node, the camera shooting horizontal angle, the pitch angle, the camera focal length, the image coordinates of the optical center point, the pixel size and other camera parameters are recorded when shooting, the object distance of any node is measured by using a laser range finder, and the parameters are saved, and the scale factors of all nodes under the shooting condition are solved by using the method provided by the invention; the multi-point dynamic deflection change of the bridge structure is identified by analyzing the image vibration change of the node part, and the selected node to be analyzed is shown in fig. 16. And finally, measuring the dynamic deflection change of the node to be analyzed by using a dial indicator displacement meter as a reference result to compare the accuracy of the identification result.
Extracting multi-point pixel displacement by using a template matching method, firstly, extracting a region of interest, wherein the region of interest is a truss node, namely the truss node to be analyzed is extracted, then traversing node vibration image sequences of all frames according to the template matching method, carrying out zero-filling convolution calculation by taking node vibration images of the previous frame as templates, calculating characteristic matching points (H2 and L2) of the next frame image matched with the positions (H1 and L1) of the previous frame image according to the position of the calculated convolution calculation characteristic value highest, and calculating pixel vibration displacement between the previous frame and the next frame according to the position of the corresponding matching point, wherein a calculation formula is shown as a formula (8) -a formula (11)
H2,L2＝maxIndex(SI)； (9)
Wherein n11 is the width dimension of the previous frame time image, n12 is the height dimension of the previous frame time image, I is the width position of the convolution template after zero padding, j is the height position of the convolution template after zero padding, I 1 (x, y) is the pixel value of the previous frame moment image at the x, y position, I 2 (i+x, j+y) is the pixel value of the image at the position i+x, j+y at the next frame time, H 1 And H is 2 The positions of the matching characteristic points corresponding to the previous frame and the following frame in height are respectively L 1 And L is equal to 2 The positions of the matching feature points corresponding to the front frame and the rear frame in the width direction are respectively calculated, the total number of the positions of the m1 matching feature points in the height direction is calculated, the total number of the positions of the m2 matching feature points in the width direction is calculated, delta H is the calculated vibration displacement between the front frame and the rear frame, and delta L is the calculated horizontal displacement between the front frame and the rear frame.
And (3) obtaining pixel vibration displacement of a plurality of measuring points through calculation, converting the pixel vibration displacement into actual displacement through a multipoint scale factor obtained through calculation of a formula (7), comparing a calculated displacement result with a measurement result of a dial indicator displacement meter, and finally obtaining a calculated displacement comparison result of the node to be analyzed, wherein the displacement comparison result is shown in figures 17-19. The standard deviation of the displacement estimation deviation is calculated according to the following formula (12) -formula (13):
wherein,,
for the reference displacement of the i-th moment point measured by the dial indicator displacement meter, +.>
For combining the ratios provided by the invention by template matchingDisplacement result, x of ith moment point calculated by example factor calculation method i The displacement estimation deviation of the ith moment is represented by n, the total number of displacement moment is represented by n, and the standard deviation of the displacement estimation deviation is represented by sigma.
The measuring result of the dynamic deflection change of the nodes 1-6 is shown in fig. 17, the error calculation result is shown in fig. 18, and it can be seen that the method for measuring the bridge multipoint dynamic deflection during off-axis measurement provided by the embodiment of the invention has the beneficial effects that:
after the pixel displacement of the multiple measuring points is obtained, the scaling factors of all measuring points can be calculated by only measuring the object distance at any point of the object plane or the actual size of any feature object of the object plane, wherein the camera angle comprises a camera horizontal angle and a camera pitch angle and combining known camera internal parameters comprising the camera focal length, the image coordinates of the optical center point and the pixel size, so that the conversion from the pixel displacement of the multiple measuring points to the actual displacement is realized, and the multi-point dynamic deflection change of the bridge is obtained. The method provided by the invention has the advantages of simple calculation and convenient application, and can rapidly and accurately calculate the dynamic deflection change curves of a plurality of measuring points.
Example 4:
FIG. 19 is a schematic diagram of the architecture of a full field scale factor meter apparatus for off-axis measurement according to an embodiment of the invention. The full field scale factor meter apparatus for off-axis measurement of this embodiment includes one or more processors 21 and memory 22. In fig. 19, a processor 21 is taken as an example.
The processor 21 and the memory 22 may be connected by a bus or otherwise, which is illustrated in fig. 19 as a bus connection.
The memory 22 acts as a non-volatile computer readable storage medium that can be used to store non-volatile software programs and non-volatile computer executable programs, such as the full field scale factor meter method for off-axis measurements in example 1. The processor 21 performs a full field scale factor meter method for off-axis measurements by running non-volatile software programs and instructions stored in the memory 22.
The memory 22 may include high-speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, memory 22 may optionally include memory located remotely from processor 21, which may be connected to processor 21 via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The program instructions/modules are stored in the memory 22, which when executed by the one or more processors 21, perform the full field scale factor meter method for off-axis measurement of embodiment 1 described above, e.g., perform the various steps shown in fig. 1, 13 and 16 described above.
It should be noted that, because the content of information interaction and execution process between modules and units in the above-mentioned device and system is based on the same concept as the processing method embodiment of the present invention, specific content may be referred to the description in the method embodiment of the present invention, and will not be repeated here.
Those of ordinary skill in the art will appreciate that all or a portion of the steps in the various methods of the embodiments may be implemented by a program that instructs associated hardware, the program may be stored on a computer readable storage medium, the storage medium may include: read Only Memory (ROM), random access Memory (RAM, random Access Memory), magnetic or optical disk, and the like.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (8)
1. The method for measuring the multi-point dynamic deflection of the bridge during off-axis measurement is characterized by comprising the following steps of:
shooting bridge vibration videos under the off-axis measurement condition, and reading a camera horizontal angle and a camera pitch angle through a camera;
selecting a plurality of measuring points according to the bridge vibration video, selecting an interested region of each measuring point, and extracting pixel displacement of the plurality of measuring points from the bridge vibration video by using a matching algorithm;
after the actual size of the object plane of the first feature is obtained, calculating to obtain a central point scale factor of the first feature;
calculating to obtain the object distance between the camera and the central point of the first feature of the measured object plane by combining the image coordinates of the central point of the first feature and the corresponding central point scale factors of the central point with the camera horizontal angle, the camera pitch angle and the camera internal parameters;
calculating all measuring point scale factors by combining the object distance of the first characteristic of the object plane of the camera with the camera horizontal angle, the camera pitch angle and the camera internal parameters;
and calculating to obtain the actual physical displacement of the corresponding measuring point according to the scale factors of all the measuring points and the pixel displacement of the plurality of measuring points.
2. The method for measuring bridge multipoint dynamic deflection during off-axis measurement according to claim 1, wherein the extracting pixel displacement of a plurality of measuring points in bridge vibration video by using a matching algorithm specifically comprises:
H 2 ,L 2 ＝maxIndex(SI)；
wherein n11 is the width dimension of the previous frame time image, n12 is the height dimension of the previous frame time image, i is the width position of the convolution template after zero padding, and j is the height position of the convolution template after zero padding; i 1 (x, y) is the previous framePixel values of the engraving image at x, y positions, I 2 (i+x, j+y) is the pixel value of the image at the i+x, j+y position at the next frame time; h 1 And H is 2 The positions of the matching characteristic points corresponding to the previous frame and the following frame in height are respectively L 1 And L is equal to 2 The positions of the matching feature points corresponding to the front frame and the rear frame in the width direction are respectively calculated, the total number of the positions of the m1 matching feature points in the height direction is calculated, the total number of the positions of the m2 matching feature points in the width direction is calculated, delta H is the calculated vibration displacement between the front frame and the rear frame, and delta L is the calculated horizontal displacement between the front frame and the rear frame.
3. The method for measuring bridge multipoint dynamic deflection at off-axis measurement according to claim 2, wherein the central point scale factor of the first feature is a scale factor SF of an image point of the first feature corresponding to an actual object plane size of the first feature First one The center point scale factor SF of the first feature First one The calculation formula is as follows:
d known is the actual size of the object plane; i known The corresponding pixel length on the image is the known physical object plane dimension.
4. The method for measuring bridge multipoint dynamic deflection during off-axis measurement according to claim 3, wherein the object distance D between the camera and the center point of the first feature of the object plane is calculated by combining the camera horizontal angle, the camera pitch angle and the camera internal reference through the image coordinates of the center point of the first feature and the corresponding center point scale factors thereof, specifically:
wherein:
SF first one A scale factor that is a first feature; (x) 0 ，y 0 ) The center point image coordinates of the first feature; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ，y c ) The coordinates of the optical center point of the camera; alpha is the camera pitch angle; beta is the camera horizontal angle.
5. The method for measuring bridge multipoint dynamic deflection during off-axis measurement according to claim 4, wherein the object distance of the first feature of the object plane is measured by the camera, and the camera horizontal angle, the camera pitch angle and the camera internal reference are combined to calculate and obtain all measuring point scale factors SF i The method specifically comprises the following steps:
wherein:
d is the object distance of the first feature; (x) 0 ，y 0 ) The image coordinates of the object distance point are measured for the image coordinates of the central point of the first feature or directly; f is the focal length of the camera; l (L) ps The size of the camera pixel; (x) c ，y c ) Imaging coordinates for a camera photo-center point; (x) i ，y i ) For waiting for SF i Is defined by the image coordinates of (a); alpha is the camera pitch angle; beta is the camera horizontal angle.
6. The method for measuring bridge multipoint dynamic deflection during off-axis measurement according to claim 1, wherein obtaining the physical object plane dimension of the first feature comprises:
according to the form and actual size of each component which is imported in the database and forms the bridge;
obtaining an alternative target object matched with each corresponding component in the form in the video frame through image matching;
synchronously analyzing the pixel displacement of the identified candidate target object while analyzing the pixel displacement of a plurality of measuring points in the bridge vibration video;
and screening one of the candidate target objects, the pixel displacement of which meets the preset condition, from the candidate target objects to serve as the first characteristic, and taking the actual size of the corresponding screened candidate target object as the actual size of the object plane of the first characteristic.
7. The method for measuring bridge multipoint dynamic deflection during off-axis measurement according to claim 6, wherein the preset conditions specifically comprise:
taking the average pixel displacement of each measuring point as a reference, wherein the pixel displacement of the alternative target object is less than 50% of the average pixel displacement+10% and less than 70% of the minimum pixel displacement in the measurement point+10％。
8. A bridge multipoint dynamic deflection measuring device for off-axis measurement, the device comprising:
at least one processor; and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor for performing the bridge multi-point dynamic deflection measurement method of any one of claims 1-7 when measured off-axis.
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| CN116309672A (en) * | 2023-05-23 | 2023-06-23 | 武汉地震工程研究院有限公司 | Night bridge dynamic deflection measuring method and device based on LED targets |
| CN116678337A (en) * | 2023-06-08 | 2023-09-01 | 交通运输部公路科学研究所 | Image recognition-based bridge girder erection machine girder front and rear pivot point position height difference and girder deformation monitoring and early warning system and method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116309672A (en) * | 2023-05-23 | 2023-06-23 | 武汉地震工程研究院有限公司 | Night bridge dynamic deflection measuring method and device based on LED targets |
| CN116678337A (en) * | 2023-06-08 | 2023-09-01 | 交通运输部公路科学研究所 | Image recognition-based bridge girder erection machine girder front and rear pivot point position height difference and girder deformation monitoring and early warning system and method |
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