CN114964048A - Underwater vision measuring device and measuring method based on ray refraction tracking - Google Patents
Underwater vision measuring device and measuring method based on ray refraction tracking Download PDFInfo
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Abstract
An underwater vision measuring device based on light refraction tracking comprises a sealed cabin body, a signal transmission cable, a camera, a line laser and an electric translation table, wherein the camera, the line laser and the electric translation table are arranged in the sealed cabin body; one end of the signal transmission cable is respectively connected with the camera, the line laser and the electric translation table, and the other end of the signal transmission cable is connected with an external computer. The invention establishes a vision measurement model which takes the thickness of the refraction surface into consideration and does not need underwater calibration. The influence of multiple refractions on a vision measurement model is fully considered, the actual propagation path of the light in underwater measurement is accurately described, and the measurement precision of the system is improved; through the vertical projection geometric analysis, the constraint condition for avoiding underwater calibration is determined, and the calibration process of the underwater measurement system is simplified.
Description
Technical Field
The invention belongs to the field of underwater optical detection, and particularly relates to an underwater vision measurement method based on light refraction tracking.
Background
In recent years, the development pace of ocean strategy is continuously accelerated, the fields of underwater engineering construction, submarine surveying, underwater structure defect detection and the like are gradually expanded, and the underwater topography measurement technology is increasingly important. At present, the underwater three-dimensional information acquisition technology commonly used at home and abroad mainly comprises acoustic measurement and optical measurement. Due to inherent physical characteristics of the acoustic measurement technology, when underwater measurement is carried out, the acoustic wave scanning range is not suitable to be controlled, and the precision cannot meet actual requirements when remote measurement is carried out. Therefore, the acoustic measurement method cannot meet the high precision requirement in underwater engineering applications.
With the rapid development of computer vision technology, the vision measurement technology based on the optical measurement method is widely applied due to the advantages of high precision, strong real-time performance, non-contact property and the like. In the underwater imaging process, light rays pass through different media such as air, the upper surface of glass, the lower surface of glass, water and the like, and the traditional linear measurement model in the air is not applicable due to refraction influence. In order to solve the problem, chinese patent CN102269587A proposes an underwater three-dimensional redrawing apparatus and redrawing method based on a controllable plane. In the three-dimensional redrawing process, the reflecting mirror is controlled to rotate, and the structured light reflected by the galvanometer is used for scanning an underwater target to be detected, so that the device is complex, and meanwhile, the light plane needs to be refracted and corrected, and the process is relatively complicated; in the process of three-dimensional reconstruction of an underwater target, the Chinese patent CN103971406A does not consider the influence of refraction on the coordinates of the fringe pixel points, so that the measurement error is large, and the reconstruction precision is difficult to meet the actual requirement; the chinese patent CN105698767A adopts a forward mapping bilinear difference method to restore the underwater image into an image in the air, and uses a binocular measurement system to restore three-dimensional information. Although the influence of refraction is considered, a mode of combining air calibration and underwater calibration is needed, the calibration process is complicated, the development of actual work is not facilitated, and meanwhile, approximate substitution is mostly adopted when the distance from the optical center of the camera to the refraction plane is calibrated, and the later-stage precision analysis is not facilitated; chinese patent CN111006610A proposes an underwater three-dimensional measurement data correction method based on structured light three-dimensional measurement, establishes a data correction formula, fully considers the influence of refraction on measurement, neglects the thickness of a glass refraction surface, does not conform to the actual light propagation path, and cannot ensure the measurement precision.
Through a large amount of data analysis and experiments, the method can solve some specific problems of underwater measurement, but the underwater structure light vision measurement still faces the following problems: firstly, how to reduce the calibration complexity and improve the portability of an underwater measurement system is realized, and the method is conveniently and quickly applied to underwater engineering operation; secondly, aiming at the influence brought by the nonlinear refraction, how to improve the precision of the underwater measurement system and meet the requirements of actual production and scientific research.
Disclosure of Invention
In order to meet the requirement of underwater vision measurement, the invention aims to overcome the existing defects and provides an underwater vision measurement device and a measurement method based on ray refraction tracking. The underwater refraction measurement model considering the thickness of the refraction surface is established, underwater calibration operation is avoided, the underwater target to be measured can be conveniently, rapidly and high-precision three-dimensional measured, and the three-dimensional shape information of the target to be measured is accurately obtained.
The object of the invention is achieved in the following way:
an underwater vision measuring device based on ray refraction tracking, the measuring device comprising: the laser line laser device is arranged on a sliding block of the electric translation table, the electric translation table is fixed on the bottom surface of the sealed cabin body, a camera support is further fixed on the bottom surface, and the camera is fixed on the camera support; one end of the signal transmission cable is connected with the camera, the line laser and the electric translation table respectively, the other end of the signal transmission cable is connected with an external computer to remotely supply power to the camera, the line laser and the electric translation table, remotely convey data of the camera and the line laser to the external computer, remotely convey a control command generated by the external computer to the camera, the line laser and the electric translation table, and the camera, the line laser and the electric translation table act according to the control command.
And a transparent glass window is arranged on one side surface of the sealed cabin body.
The included angle between the optical axis of the camera and the optical axis of the line laser is 30-50 degrees.
And the top of the sealed cabin body is provided with a suspension device.
A measuring method of an underwater vision measuring device based on ray refraction tracking comprises the following steps:
s1: analyzing the vector change relation of the light direction when the light passes through different media such as air, the upper surface of the glass, the lower surface of the glass, water and the like, and determining the spatial layout condition without underwater calibration;
s2: establishing a visual measurement model considering the thickness of a refraction surface and avoiding underwater calibration based on the spatial layout condition without underwater calibration;
s3: carrying out land calibration on parameters of the underwater vision measurement model, and carrying out underwater measurement work after solving unknown parameters in the measurement model;
s4: collecting an underwater measurement image scanned by a laser, extracting and optimizing a laser stripe central line after carrying out noise reduction processing on the image, and obtaining a laser stripe image point coordinate;
s5: and acquiring three-dimensional measurement point cloud data by combining the coordinates of the laser stripe image points and an underwater measurement visual model, generating a three-dimensional topography map, and really restoring the surface characteristics of the target to be measured.
The spatial layout condition that does not need underwater calibration in S1 specifically includes: when the line laser projects line structure light to a measured target, according to the space geometric relationship between the straight line where the optical axis of the laser is located and the normal line of the refraction plane, the straight line where the optical axis of the line laser is located, the projection light, the normal line of the refraction plane and the four-line coplane of the refraction light can be determined when the optical axis of the line laser is perpendicular to the refraction plane to project, namely, the projection structure light plane formed by the optical axis of the line laser and the projection light and the underwater structure light plane formed by the normal line of the refraction plane and the refraction light are coplanar, and at the moment, the land light plane can be used for replacing the underwater light plane.
The specific method of S2 is as follows: with camera lightEstablishing a camera coordinate system oxyz by taking the center as an original point and the optical axis direction as a z-axis; the optical center of the line laser is used as the origin, and the direction of the optical axis is z w Establishing a world coordinate system o w x w y w z w (ii) a For underwater measured object point p 01 (x, y, z) via point p 01 Reflected light is refracted twice by the upper and lower surfaces and imaged on an image plane of the camera 4 (x u ,y u F) the incident ray intersects the refractive upper and lower surfaces at a point p 3 (x 3 ,y 3 ,z 3 ) And p 2 (x 2 ,y 2 ,z 2 ) (ii) a According to the vector form of Snell law, the optical path in the glass can be known
And light path in the air
Relation between, incident light path
And a refracted light path
The relationships between the two are respectively:
wherein
f is the focal length of the camera, and (a, b, c) is the normalized normal vector of the refraction plane
n 1 Is the relative refractive index of hollow/glass(n 1 ＝n a /n g )、n 2 Is the glass/water relative refractive index (n) 2 ＝n g /n w ) (ii) a By the intersection of line and plane
Wherein W is the thickness of the refracting surface of the glass; according to the light propagation path, the underwater measured object point p 01 (x, y, z) can use its image point p 4 (x u ,y u And f) is expressed as:
wherein
And (A, B, C and D) are calibrated structural light plane parameters.
The calibrating of the model parameters in the S3 specifically includes: calibrating internal and external parameters of a camera: keeping the position of a camera unchanged, and acquiring 16-21 checkerboard target images at different positions in the field range of the camera; calibrating the internal and external parameters of the camera by using a Matlab Calibration Toolbox to obtain an internal and external parameter matrix; calibrating the plane parameters of the structured light: starting a line laser, projecting laser stripes onto a target plane, and extracting image point information of the laser stripes; acquiring a plurality of groups of calibration points on a structured light plane by using target corner points with known image point coordinates and world coordinates and combining an intersection ratio invariant principle, wherein the coordinates of the calibration points under a camera coordinate system are (x) i ,y i ,z i ) Where i ═ 1,2,3 i +By i +Cz i + D ═ 0, where (a, B, C, D) are the respective structured-light plane parameters; taking the square sum of the Euclidean distances from the calibration point to the light plane as an objective function, and carrying out repeated iteration optimization solution on each light plane parameter (A, B, C and D); calibrating parameters of a refraction plane: acquiring measurement point cloud data on a refraction plane, namely a transparent glass window in the air, wherein the coordinate of the point cloud under a camera coordinate system is (x) j ,y j ,z j ) Wherein j is 1,2, 3.,n; these point cloud data will satisfy N p ×X 3×N ＝d 1×N Wherein X is 3×N Coefficient matrices formed for refracting the plane point clouds, N p As a normal vector parameter of the refraction plane, d 1×N Represents a planar constant vector; and solving the refraction plane parameters (a, b, c and d) by adopting a global optimization algorithm.
The step of collecting the image and optimizing and extracting the laser stripe center line by the step of S4 specifically comprises the following steps: carrying the vision measuring device on an underwater AUV, opening a camera, a laser and an electric translation table to enable the camera, the laser and the electric translation table to be in an open state, and enabling the position of the laser to return to zero; when the laser moves on the electric translation table at a constant speed, the laser stripes are projected to the surface of an underwater target to be detected, and the camera automatically acquires laser stripe images on the target to be detected at the same time interval until the laser finishes scanning the target to be detected; and carrying out noise reduction treatment such as spatial filtering on the acquired laser stripe image, and extracting the central line of the laser stripe by adopting an improved gray scale gravity center method to obtain the image point information of the laser stripe.
The step S5 of generating a three-dimensional topography map specifically includes: respectively substituting the laser stripe image point coordinates carrying the surface characteristic information of the target to be measured obtained from the step S4 into (x) in the refraction measurement model S2 u ,y u And (v) obtaining object point coordinates (x, y, z) corresponding to the image points, obtaining three-dimensional dense point cloud data of the target to be detected, generating a three-dimensional topography, and really restoring the surface characteristics of the target to be detected.
The invention has the beneficial effects that: according to the invention, when the underwater vision measurement method based on ray refraction tracking is used for acquiring the three-dimensional shape information of an underwater target to be measured, the refraction influence of rays when the rays pass through different media such as air, the upper surface of glass, the lower surface of glass, water and the like is fully considered according to the real propagation path of the rays, and the vision measurement model which considers the thickness of a refraction surface and does not need underwater calibration is established. The influence of multiple refractions on the vision measurement model is fully considered, the actual propagation path of the light in underwater measurement is accurately described, and the measurement precision of the system is improved; through the vertical projection geometric analysis, the constraint condition for avoiding underwater calibration is determined, and the calibration process of the underwater measurement system is simplified. When the method is used for measuring the underwater target to be measured, the laser scans the whole target to be measured at a constant speed, the camera continuously and automatically acquires images, dense three-dimensional point cloud data can be obtained, the surface characteristics of the target to be measured are really restored, underwater high-precision three-dimensional measurement is conveniently realized, and the method is used for guiding the aspects of defect detection of underwater structures, underwater landform drawing, underwater archaeology and the like.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
FIG. 2 is a schematic view of an underwater vision measurement system of the present invention.
FIG. 3 is a model of an underwater vision measurement method based on ray refraction tracking according to the present invention.
FIG. 4 is a flow chart of model parameter calibration.
In the figure: the system comprises a camera 1, a line laser 2, an electric translation table 3, a transparent glass window 4, a sealed cabin 5, a suspension device 6, a camera support 7, a signal transmission cable 8 and an external computer 9.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same technical meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
As shown in fig. 2, an underwater vision measuring device based on ray refraction tracking, the measuring device comprises: the laser camera comprises a sealed cabin body, a signal transmission cable, a camera 1, a line laser 2 and an electric translation table 3, wherein the camera 1, the line laser 2 and the electric translation table are arranged in the sealed cabin body, the line laser 2 is arranged on a sliding block 4 of the electric translation table 3, the electric translation table 3 is fixed on the bottom surface of the sealed cabin body 5, a camera support 7 is further fixed on the bottom surface, and the camera 1 is fixed on the camera support 7; one end of the signal transmission cable is connected with the camera, the line laser and the electric translation platform respectively, the other end of the signal transmission cable is connected with an external computer 9 to remotely supply power to the camera, the line laser and the electric translation platform, remotely convey data of the camera and the line laser to the external computer, remotely convey a control command generated by the external computer to the camera, the line laser and the electric translation platform, and the camera, the line laser and the electric translation platform are based on the corresponding action of the control command. In the measuring process, the camera is kept still, the laser moves at a constant speed on the electric translation table, wherein the optical axis of the laser is always vertical to the refraction plane, and the included angle between the optical axis of the camera and the optical axis of the laser is controlled within the range of 30-50 degrees.
And a transparent glass window is arranged on one side surface of the sealed cabin body.
The top of the sealed cabin body is provided with a hanging device 6, preferably, the hanging device can be selected from a hook, the hook is the prior art, and the structure is not described in detail herein.
The electric translation stage adopts the prior art, and can refer to the electric translation stage structure in application number CN 2019215421143.
An underwater vision measurement method based on ray refraction tracking is shown in fig. 1, and mainly comprises the following steps:
step 1: analysis of spatial geometrical relationships
During projection, as shown in FIG. 3, light is projected in the air
And the light beam is projected to a refraction glass surface and reaches an underwater surface S to be detected after multiple times of refraction. When projecting the optical axis
Perpendicular plane of refraction pi 11 Projection, projection optical axis
Normal to the plane of refraction
Parallel. Projection optical axis
And projecting light
Intersecting the projection center P. Thus, the projection optical axis
Projecting incident light
And projecting the refracted rays
Three lines coplanar with the projection light plane pi 2 . That is, when the projection device is perpendicular to the refraction plane π 1 Projection (i.e. projection optical axis)
Perpendicular to the plane of refraction pi 11 And through the projection light plane pi 2 ) When the projection plane in the glass is coplanar with the projection plane in the air. Assuming that the upper and lower refracting surfaces of the glass are parallel to each other, the normal directions of the two refracting surfaces are both
Projecting incident light according to multiple refractometric analysis
And projecting the refracted rays
At normal to the plane of refraction
The three lines are coplanar, namely the underwater projection light plane, the projection light plane in the glass and the projection light plane in the air are the same plane.
Step 2: underwater visual refraction measurement model
As shown in fig. 3, oxyz is the camera coordinate system and OXY is the camera image plane coordinateThe mark is a mark which is a mark of,
and
the direction vectors of incident light in water, refracted light in glass and refracted light in air in the imaging process are respectively shown.
And
the direction vectors of the projection incident light in the air, the refraction light in the glass and the projection refraction light in the water are respectively.
Is a plane of refraction pi 1 And normalizing the normal vector parameters. W is the thickness of the glass medium, n a 、n w And n g The refractive indices of air, water and glass.
For projecting structured light planes pi 2 Normalized normal vector parameters of (1). Projection light plane pi 2 Point of intersection p with surface of underwater object 01 ,…,p 0i Is the measured point on the surface of the underwater object.
With the measured point p 01 (x, y, z) for example, the imaging process was analyzed. Warp point p 01 Reflected light passes through interface pi 11 And pi 12 After twice refraction, the image is formed on a point p on the image plane of the camera 4 Incident light intersects the refracting upper and lower planes at a point p 3 And p 2 . Object point p 01 And point p 2 Forming incident light rays under water
Intersection point p 3 And p 2 Forming refraction rays in glass
Refraction vector in the propagation path of imaging light in air
From the image point p of the object to be measured 4 (x u ,y u F) is represented by the camera origin o
Intersection point p of refracting planes 3 (x 3 ,y 3 ,z 3 ) Refracting light by imaging
And a refraction plane pi 11 And (4) intersecting to obtain.
The upper and lower refracting surfaces of the glass are parallel to each other, and the normal directions of the two refracting surfaces are the same
Light path in glass according to vector form of Snell's law
And light path in the air
The relationship between is
Wherein
n 1 Is a relative refractive index (n) of hollow/glass 1 ＝n a /n g ) (ii) a The intersection point p of the lower plane of the glass can be obtained according to the intersection of the line and the plane 2 (x 2 ,y 2 ,z 2 )。
After passing through two parallel refraction surfaces, the incident light path
And refracted light path
The relationship between is
Wherein
n 2 Is the glass/water relative refractive index (n) 2 ＝n g /n w ). According to the relation of point and line, the measured object point p 01 (x, y, z) can be represented as
Wherein, the lambda is a proportionality coefficient and is determined by the position of the measured object point. Plane of projected light pi 2 And underwater incident light path
Intersect at the point of measurement, i.e.
From this, it can be found that the proportionality coefficient λ in the formula (1) is
Underwater measured point p 01 (x, y, z) can be represented as
Step 3: model parameter calibration
As shown in fig. 4, before the model parameter calibration, the camera and the electric translation stage are started, and the parameter calibration flow is as shown in fig. 4.
(1) Calibrating an internal parameter matrix and an external parameter matrix of the camera: firstly, adjusting the aperture of the camera and keeping the aperture unchanged; changing the position of the target for multiple times within the visual field range of the camera, and collecting 16-21 target images; and calibrating the internal and external parameters of the camera by utilizing a Matlab Calibration Toolbox to obtain an internal and external parameter matrix.
(2) And (3) structured light plane calibration: starting a line laser, projecting a bright line laser stripe to a target plane, enabling the laser to move at a constant speed on a translation table, automatically acquiring target plane images by a camera at the same time interval, and extracting the laser stripe in each image to obtain light stripe image point information of a plurality of structured light planes; changing the depth position of the target, repeating the steps, and obtaining image point information of a plurality of laser stripes on the structured light plane; suppose that one of the laser stripes projected onto the target plane is a straight line L 2 ，E 1 、E 2 、E 3 Is located on a straight line L on the plane target 1 The coordinates of the characteristic points in the world coordinate system are respectively E 1 (x w1 ,y w1 ,0)、E 2 (x w2 ,y w2 ,0)、E 3 (x w3 ,y w3 0), the image point corresponding to the feature point is e 1 (X u1 ,Y u1 )、e 2 (X u2 ,Y u2 )、e 3 (X u3 ,Y u3 ) Intersection E of straight lines where collinear feature points on the light stripe and the target plane are located x (x wx ,y wx 0) is the index point and the corresponding image point is e x (X ux ,Y ux ). Under the condition of the image coordinate system,obtaining the image point coordinate e of the calibration point by solving the intersection point of the fitting straight line where the characteristic point is located and the fitting straight line where the light stripe is located x . Collinear point (e) 1 ,e 2 ,e 3 ,e x ) Defined as a cross ratio of
According to the principle of constant ratio
Cr(e 1 ,e 2 ,e 3 ,e x )＝Cr(E 1 ,E 2 ,E 3 ,E x )
The coordinate of the calibration point in the world coordinate system is
Wherein
In actual calculation, only 3 feature points are involved in cross ratio calculation, so the calculation result is easily influenced by the noise of the feature points. In order to overcome the influence of noise, the number N of collinear feature points on the selected target is more than 3, and the collinear feature points are calculated
Calculating the average value of the characteristic points to obtain the world coordinate value of the calibration point; the coordinate (x) of the calibration point in the camera coordinate system can be obtained by the coordinate system conversion i ,y i ,z i ) Where i ═ 1,2,3 i +By i +Cz i + D ═ 0, where (a, B, C, D) are the respective structured-light plane parameters; and (3) performing iterative optimization solution on each optical plane parameter (A, B, C and D) for multiple times by taking the square sum of the Euclidean distances from the calibration point to the optical plane as an objective function.
(3) Calibrating a refraction plane: will be transparentReplacing the glass window with a white opaque plate, performing surface measurement on the refraction surface by using a structured light system, and acquiring measurement point cloud data of the refraction surface in the air, wherein the coordinate of the point cloud under a camera coordinate system is (x) j ,y j ,z j ) Wherein j is 1,2, 3. These point cloud data will satisfy N p ×X 3×N ＝d 1×N Wherein X is 3×N Coefficient matrices formed for refracting the plane point clouds, N p As a normal vector parameter of the refraction plane, d 1×N Represents a planar constant vector; and solving the refraction plane parameters (a, b, c and d) by adopting a global optimization algorithm.
Step 4: underwater topography measurement
Firstly, checking the tightness of visual equipment, carrying the visual equipment on an underwater AUV (autonomous Underwater vehicle), moving the AUV to a target to be tested to hover within a range of 1-2 meters, remotely starting a camera, a line laser and an electric translation table, and zeroing the position of the line laser; and then projecting laser stripes to the surface of an underwater target to be detected, moving the line laser on the electric translation table at a constant speed, and automatically acquiring light stripe images on the target to be detected by the camera at the same time interval until the laser finishes scanning the target to be detected. Transmitting the acquired image information back to a computer in real time, performing noise reduction processing such as spatial filtering on the laser stripe image, extracting and optimizing the central line of the laser stripe by adopting an improved gray scale gravity center method, and acquiring the image point information of the laser stripe; respectively substituting the obtained laser stripe image point coordinates carrying the surface characteristic information of the target to be measured into (x) in the refraction measurement model u ,y u And (v) obtaining object point coordinates (x, y, z) corresponding to the image points, obtaining three-dimensional dense point cloud data of the target to be detected, generating a three-dimensional topography, and really restoring the surface characteristics of the target to be detected.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive changes in the technical solutions of the present invention.
Claims (10)
1. The utility model provides an underwater vision measuring device based on ray refraction pursuit which characterized in that: the measuring device includes: the device comprises a sealed cabin body, a signal transmission cable, a camera (1), a line laser (2) and an electric translation table (3), wherein the camera (1), the line laser (2) and the electric translation table are arranged in the sealed cabin body, the line laser (2) is arranged on a sliding block (4) of the electric translation table (3), the electric translation table (3) is fixed on the bottom surface of the sealed cabin body (5), a camera support (7) is further fixed on the bottom surface, and the camera (1) is fixed on the camera support (7); one end of the signal transmission cable is connected with the camera, the line laser and the electric translation platform respectively, the other end of the signal transmission cable is connected with an external computer (9) to remotely supply power to the camera, the line laser and the electric translation platform, remotely convey data of the camera and the line laser to the external computer, remotely convey a control command generated by the external computer to the camera, the line laser and the electric translation platform, and the camera, the line laser and the electric translation platform are according to the control command corresponding action.
2. The underwater vision measuring device based on ray refraction tracking of claim 1, wherein: and a transparent glass window is arranged on one side surface of the sealed cabin body.
3. The underwater vision measuring device based on ray refraction tracking of claim 1, wherein: the included angle between the optical axis of the camera and the optical axis of the line laser is 30-50 degrees.
4. The underwater vision measuring device based on ray refraction tracking of claim 1, wherein: the top of the sealed cabin body is provided with a suspension device (6).
5. A measurement method of the underwater vision measurement device based on ray refraction tracking according to any one of claims 1 to 4, characterized in that: the method comprises the following steps:
s1: analyzing the vector change relation of the light direction when the light passes through different media such as air, the upper surface of the glass, the lower surface of the glass, water and the like, and determining the spatial layout condition without underwater calibration;
s2: establishing a visual measurement model considering the thickness of a refraction surface and avoiding underwater calibration based on the spatial layout condition without underwater calibration;
s3: carrying out land calibration on parameters of the underwater vision measurement model, and carrying out underwater measurement work after solving unknown parameters in the measurement model;
s4: collecting an underwater measurement image scanned by a laser, extracting and optimizing a laser stripe central line after carrying out noise reduction processing on the image, and obtaining a laser stripe image point coordinate;
s5: and acquiring three-dimensional measurement point cloud data by combining the coordinates of the laser stripe image points and an underwater measurement visual model, generating a three-dimensional topography map, and really restoring the surface characteristics of the target to be measured.
6. The method for measuring an underwater vision measuring device based on ray refraction tracking as claimed in claim 5, wherein: the spatial layout condition which does not need underwater calibration in S1 specifically includes: when the line laser projects line structure light to a measured target, according to the space geometric relationship between the straight line where the optical axis of the laser is located and the normal line of the refraction plane, the straight line where the optical axis of the line laser is located, the projection light, the normal line of the refraction plane and the four-line coplane of the refraction light can be determined when the optical axis of the line laser is perpendicular to the refraction plane to project, namely, the projection structure light plane formed by the optical axis of the line laser and the projection light and the underwater structure light plane formed by the normal line of the refraction plane and the refraction light are coplanar, and at the moment, the land light plane can be used for replacing the underwater light plane.
7. The method for measuring an underwater vision measuring device based on ray refraction tracking as claimed in claim 5, wherein: the specific method of S2 comprises the following steps: establishing a camera coordinate system oxyz by taking the optical center of the camera as an origin and the optical axis direction as a z-axis; the optical center of the line laser is used as the origin, and the direction of the optical axis is z w Establishing a world coordinate system o w x w y w z w (ii) a For underwater measured object point p 01 (x,y,z)，Warp point p 01 Reflected light is refracted twice by the upper and lower surfaces and imaged on an image plane of the camera 4 (x u ,y u F) the incident ray intersects the refractive upper and lower surfaces at a point p 3 (x 3 ,y 3 ,z 3 ) And p 2 (x 2 ,y 2 ,z 2 ) (ii) a According to the vector form of Snell law, the optical path in the glass can be known
And light path in the air
Relation between, incident light path
And a refracted light path
The relationships between the two are respectively:
wherein
f is the focal length of the camera, and (a, b, c) is the normalized normal vector of the refraction plane
n 1 Is a relative refractive index (n) of empty/glass 1 ＝n a /n g )、n 2 Is the glass/water relative refractive index (n) 2 ＝n g /n w ) (ii) a ByLine and plane are intersected to know
Wherein W is the thickness of the refracting surface of the glass; according to the light propagation path, the underwater measured object point p 01 (x, y, z) can use its image point p 4 (x u ,y u And f) is expressed as:
wherein
And (A, B, C and D) are calibrated structural light plane parameters.
8. The method for measuring an underwater vision measuring device based on ray refraction tracking as claimed in claim 5, wherein: the calibrating of the model parameters in the S3 specifically includes: calibrating internal and external parameters of a camera: keeping the position of a camera unchanged, and acquiring 16-21 checkerboard target images at different positions in the field range of the camera; calibrating the internal and external parameters of the camera by using a Matlab Calibration Toolbox to obtain an internal and external parameter matrix; calibrating the plane parameters of the structured light: starting a line laser, projecting laser stripes onto a target plane, and extracting image point information of the laser stripes; acquiring a plurality of groups of calibration points on a structured light plane by using target corner points with known image point coordinates and world coordinates and combining an intersection ratio invariant principle, wherein the coordinates of the calibration points under a camera coordinate system are (x) i ,y i ,z i ) Where i ═ 1,2,3 i +By i +Cz i + D ═ 0, where (a, B, C, D) are the respective structured-light plane parameters; taking the square sum of the Euclidean distances from the calibration point to the light plane as an objective function, and carrying out repeated iteration optimization solution on parameters (A, B, C and D) of each light plane; calibrating parameters of a refraction plane: acquiring measurement point cloud data on a refraction plane, namely a transparent glass window in the air, wherein the coordinate of the point cloud under a camera coordinate system is (x) j ,y j ,z j ) Wherein j is 1,2, 3. These point cloud data will satisfy N p ×X 3×N ＝d 1×N Wherein X is 3×N Coefficient matrices formed for refracting the plane point clouds, N p As a normal vector parameter of the refraction plane, d 1×N Represents a planar constant vector; and solving the refraction plane parameters (a, b, c and d) by adopting a global optimization algorithm.
9. The method for measuring an underwater vision measuring device based on ray refraction tracking as claimed in claim 5, wherein: the step of collecting the image and optimizing and extracting the laser stripe center line by the step of S4 specifically comprises the following steps: carrying the vision measuring device on an underwater AUV, opening a camera, a laser and an electric translation table to enable the camera, the laser and the electric translation table to be in an open state, and enabling the position of the laser to return to zero; when the laser moves on the electric translation table at a constant speed, the laser stripes are projected to the surface of an underwater target to be detected, and the camera automatically acquires laser stripe images on the target to be detected at the same time interval until the laser finishes scanning the target to be detected; and carrying out noise reduction treatment such as spatial filtering on the acquired laser stripe image, and extracting the central line of the laser stripe by adopting an improved gray scale gravity center method to obtain the image point information of the laser stripe.
10. The method for measuring an underwater vision measuring device based on ray refraction tracking as claimed in claim 5, wherein: the step S5 of generating a three-dimensional topography map specifically includes: respectively substituting the laser stripe image point coordinates carrying the surface characteristic information of the target to be measured obtained from the step S4 into (x) in the refraction measurement model S2 u ,y u And (v) obtaining object point coordinates (x, y, z) corresponding to the image points, obtaining three-dimensional dense point cloud data of the target to be detected, generating a three-dimensional topography, and really restoring the surface characteristics of the target to be detected.
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| CN116242253A (en) * | 2023-05-11 | 2023-06-09 | 西南科技大学 | Underwater concrete apparent laser line three-dimensional scanning measurement method |
| CN116817794A (en) * | 2023-06-27 | 2023-09-29 | 浙江大学 | Underwater high-precision three-dimensional imaging device and method based on structured light |
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| CN116242253A (en) * | 2023-05-11 | 2023-06-09 | 西南科技大学 | Underwater concrete apparent laser line three-dimensional scanning measurement method |
| CN116242253B (en) * | 2023-05-11 | 2023-07-07 | 西南科技大学 | Underwater concrete apparent laser line three-dimensional scanning measurement method |
| CN116817794A (en) * | 2023-06-27 | 2023-09-29 | 浙江大学 | Underwater high-precision three-dimensional imaging device and method based on structured light |
| CN116817794B (en) * | 2023-06-27 | 2024-02-13 | 浙江大学 | Underwater high-precision three-dimensional imaging device and method based on structured light |
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