A calibration and reconstruction method for a three-dimensional measurement system and a three-dimensional measurement system

Abstract

The invention discloses a calibration and reconstruction method for a three-dimensional measurement system and a three-dimensional measurement system. The method comprises: using orthogonal bidirectional phase information to track the corresponding light of each pixel of an imaging device in a measurement space, constructing a first loss function to calibrate light parameters; using a white-bottom plane plate printed with multiple reference points as a projection receiving plane target and placing it in multiple positions in front and back in the measurement space with different postures, projecting a single-direction phase-shifted fringe pattern onto it by a projector, collecting the corresponding projection image by an imaging device, constructing a second loss function, and calculating and acquiring the posture parameters of the projection receiving plane target; determining the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target, fitting the phase mapping coefficient of the pixel light of the imaging device; establishing a lookup table; collecting the image of the object to be measured after the pattern is projected to obtain the phase value, obtaining the phase mapping coefficient according to the lookup table, and calculating the coordinates of the object to be measured.

Description

Technical Field

[0001] The present invention relates to the field of three-dimensional imaging technology, and in particular to a calibration and reconstruction method of a three-dimensional measurement system and a three-dimensional measurement system. Background Art

[0002] The calibration method of the traditional fringe projection 3D measurement system is mainly based on the perspective projection model, focusing on the calibration of the system's internal parameters. It requires strict analysis of the internal optical layout of the imaging system, lens distortion and other factors to construct the correspondence between the object point and the system image point. The most classic projection model calibration method is the pinhole camera model, which idealizes the object-image relationship into pinhole imaging. The calibration parameters mainly include the principal point coordinates and the equivalent focal length. Taking into account the lens distortion, it also includes radial distortion and tangential distortion. The pinhole model is suitable for the calibration of cameras equipped with conventional lenses, but it is difficult to apply to telecentric lenses, wide-angle lenses, light field cameras and some unknown imaging systems. Moreover, for lenses with asymmetry or large distortion, the polynomial fitting distortion model cannot accurately characterize them, making the traditional 3D measurement operation complicated and low in accuracy. Summary of the invention

[0003] The embodiment of the present invention provides a calibration and reconstruction method of a three-dimensional measurement system and a three-dimensional measurement system to simplify operation and improve the accuracy of light calibration and three-dimensional reconstruction.

[0004] In a first aspect, an embodiment of the present invention provides a calibration and reconstruction method for a three-dimensional measurement system, which includes: imaging device pixel light calibration: using orthogonal two-way phase information to track the corresponding light of each pixel of the imaging device in the measurement space, and constructing a first loss function to calibrate the light parameters; wherein the orthogonal two-way directions refer to the horizontal and vertical directions, and the measurement space is the area at the junction of the clearly focused field of view of the imaging device and the clear projection area of ​​the projector; associating the imaging device pixel light with the projection phase: using a white-bottom flat plate printed with multiple reference points as a projection receiving plane target, placing the projection receiving plane target in multiple positions in the measurement space in turn with different postures, and the projector projects a unidirectional phase shift strip to the projection receiving plane target at each posture. The imaging device collects and obtains the projection image of the projection receiving plane target at each posture, constructs a second loss function, and calculates and obtains the posture parameters of the projection receiving plane target at each posture; fits the phase mapping coefficient of the pixel light of the imaging device: determines the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target at each posture, and fits the phase mapping coefficient of the pixel light of the imaging device; establishes a lookup table: establishes a lookup table for storing the phase mapping coefficient of the pixel light of the imaging device; three-dimensional reconstruction: projects a unidirectional phase-shifted fringe pattern to the object to be measured, obtains the phase value of the surface of the object to be measured, combines the lookup table, obtains the phase mapping coefficient corresponding to the phase value of the surface of the object to be measured, and calculates and obtains the three-dimensional coordinates of the object to be measured.

[0005] Its further technical solution is: the step of calibrating the pixel light of the imaging device specifically includes the following steps: placing the display in a plurality of positions in a measurement space in turn in different postures, the display displays an orthogonal two-way phase-shifted stripe pattern at each position, and the imaging device collects and obtains the orthogonal two-way stripe image of the display at each posture; determining the corresponding point of the intersection of the light of each pixel of the imaging device and the display at each posture on the display plane of the display, minimizing the distance between the intersection of the light corresponding to each pixel of the imaging device and the display at each posture and the spatial point of the intersection in the light coordinate system, constructing a first function, calculating and obtaining the posture parameters of the display at each posture, and calibrating the parameters of the light of each pixel of the imaging device.

[0006] Its further technical solution is: the three-dimensional reconstruction step specifically includes: a projector projects a unidirectional phase-shifted fringe pattern onto the surface of the object to be measured, and a phase value of the surface of the object to be measured is calculated using a phase shift method based on an image of the object to be measured after the unidirectional phase-shifted fringe pattern is projected and acquired by an imaging device; based on the obtained phase value of the surface of the object to be measured, a phase mapping coefficient corresponding to the phase value of the surface of the object to be measured is obtained in combination with a lookup table; and based on the obtained phase value and the corresponding phase mapping coefficient, the three-dimensional coordinates of the object to be measured are calculated.

[0007] Its further technical solution is: the step of associating the pixel light of the imaging device with the projection phase specifically includes: placing the projection receiving plane target in a plurality of positions in the measurement space in turn in different postures, the projector projects a unidirectional phase-shifted fringe pattern to the projection receiving plane target of each posture, and the imaging device collects and obtains the projection image of the projection receiving plane target of each posture; minimizing the distance between the intersection of the light of the image point of each reference point and the projection receiving plane target of each posture and the spatial point of each reference point of the projection receiving plane target of each posture in the light coordinate system, constructing a second loss function, and calculating and obtaining the optimal posture parameters of the projection receiving plane target of each posture.

[0008] In a second aspect, an embodiment of the present invention provides a three-dimensional measurement system, which includes an imaging device, a projector, a display and a projection receiving plane target, wherein the imaging device is used to capture images, and the projector is used to project a unidirectional phase-shifted fringe pattern, wherein the area at the junction of the clearly focused field of view of the imaging device and the clear projection area of ​​the projector forms a measurement space; the display is arranged in the measurement space, and is used to display orthogonal bidirectional phase-shifted fringe patterns; the projection receiving plane target is arranged in the measurement space, and is used to project the unidirectional phase-shifted fringe pattern projected by the projector, and the projection receiving plane target adopts a white-bottomed plane plate printed with multiple reference points.

[0009] Its further technical solution is: the display adopts an LCD display.

[0010] The present invention provides a calibration and reconstruction method for a three-dimensional measurement system. The method uses orthogonal bidirectional phase information to track the corresponding light of each pixel of an imaging device in a measurement space to calibrate the light corresponding to each pixel of the imaging device. It only needs to determine the light equation corresponding to each pixel within the imaging depth of field, without considering the structural layout of the imaging system, thereby avoiding the complex process of strictly analyzing and establishing each imaging model, and also avoiding the accuracy loss caused by the approximate expression of lens distortion. The method associates the light corresponding to the pixel of the imaging device with the phase of the projection to determine the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target of each posture, fits the phase mapping coefficient of the pixel light of the imaging device, establishes a lookup table for storing the phase mapping coefficient of the pixel light of the imaging device, obtains the phase value of the surface of the measured object according to the image of the measured object after the projection pattern is acquired by the imaging device, and obtains the corresponding phase mapping coefficient in combination with the lookup table to directly calculate the three-dimensional coordinates of the measured object, thereby improving the three-dimensional measurement efficiency, having the potential for high-precision calibration of different types of fringe projection systems, without the need to calibrate the internal parameters of the three-dimensional measurement system, without the need to approximate the lens distortion, and having higher calibration accuracy and three-dimensional reconstruction accuracy, simple operation, and strong versatility. The three-dimensional measuring system of the present invention also has the above-mentioned functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0012] Figure 1 A schematic diagram of a flow chart of a calibration and reconstruction method for a three-dimensional measurement system provided by an embodiment of the present invention;

[0013] Figure 2 A schematic flow chart of the steps of calibrating pixel light of an imaging device in a calibration and reconstruction method of a three-dimensional measurement system provided in an embodiment of the present invention;

[0014] Figure 3 A schematic flow chart of the steps of associating the pixel light of an imaging device with the projection phase in a calibration and reconstruction method of a three-dimensional measurement system provided by an embodiment of the present invention;

[0015] Figure 4 A schematic flow chart of the three-dimensional reconstruction steps of the calibration and reconstruction method of the three-dimensional measurement system provided by an embodiment of the present invention;

[0016] Figure 5 A schematic block diagram of a three-dimensional measurement system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0018] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, the singular forms of "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. The term "and / or" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0019] See also Figure 1 , Figure 1 FIG1 is a flow chart of a calibration and reconstruction method of a three-dimensional measurement system provided by an embodiment of the present invention. As shown in FIG1 , the method includes the following steps:

[0020] Step S110, calibration of imaging device pixel light: using the orthogonal two-way phase information to track the corresponding light of each pixel of the imaging device in the measurement space, constructing a first loss function to calibrate the light parameters; wherein, the orthogonal two-way directions refer to the horizontal and vertical directions, the imaging device can be a camera, and the measurement space is the area at the junction of the imaging device's clearly focused field of view and the projector's clearly projected area. The orthogonal two-way phase information is calculated using the phase shift method using the orthogonal two-way fringe image collected by the imaging device, and the parameters of the light corresponding to each pixel of the imaging device satisfy the spatial straight line equation expressed by the following formula:

[0021]

[0022] Where ij represents the index of the pixel of the imaging device, represents the light corresponding to each pixel of the imaging device, θ ij , a ij and b ij They represent the expression coefficients of the spatial straight line where the light corresponding to the pixel is located, X ij , Y ij and Z ij The coordinates of the point on the ray that represents the pixel.

[0023] Step S120, associating the pixel light of the imaging device with the projection phase: using a white-bottom plane plate printed with multiple reference points as a projection receiving plane target, placing the projection receiving plane target in multiple positions in the measurement space in different postures, and projecting a unidirectional phase-shifted stripe pattern to the projection receiving plane target of each posture. The imaging device collects and obtains the projection image of the projection receiving plane target of each posture, constructs a second loss function, and calculates and obtains the posture parameters of the projection receiving plane target of each posture. Among them, the reference points use circular reference points, the number of reference points can be 99, and they are evenly spaced on the white plane plate. The reference points of the projection receiving plane target provide spatial constraints for obtaining the posture parameters of the projection receiving plane target. The number of positions where the projection receiving plane target is placed is greater than 5 to ensure calibration accuracy. The unidirectional phase-shifted stripe pattern can be a vertical direction, and the unidirectional phase-shifted stripe pattern can be a vertical phase-shifted stripe pattern.

[0024] Step S130, fitting the phase mapping coefficient of the pixel light of the imaging device: determining the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target of each posture, and fitting the phase mapping coefficient of the pixel light of the imaging device.

[0025] The step S130 is specifically as follows:

[0026] According to the projection image of the projection receiving plane target at each posture acquired by the imaging device, the absolute phase of the projection receiving plane target at each posture is obtained by using the phase shift method, and the phase value of the intersection point between the light corresponding to each pixel of the imaging device and the projection receiving plane target at each posture is calculated; according to the posture parameters of the projection receiving plane target at each posture calculated by the second loss function, the three-dimensional coordinates of the intersection point between the light corresponding to each pixel of the imaging device and the projection receiving plane target are calculated; according to the three-dimensional coordinates and phase value of the intersection point between the light corresponding to each pixel of the imaging device and the projection receiving plane target, the phase mapping coefficient of the pixel light of the imaging device is fitted.

[0027] Step S140, establish a lookup table: establish a lookup table for storing the phase mapping coefficients of the pixel light of the imaging device. The lookup table for the phase mapping coefficients of the light corresponding to each pixel of the imaging device is set as: , c n represents the phase mapping coefficient, P ij represents the point on the light corresponding to each pixel of the imaging device, The coefficients of the expression representing the straight line in space where the light rays corresponding to each pixel of the imaging device lie.

[0028] Step S150, 3D reconstruction: project a unidirectional phase-shifted fringe pattern onto the object to be measured, obtain the phase value of the surface of the object to be measured, obtain the phase mapping coefficient corresponding to the phase value of the surface of the object to be measured by combining with the lookup table, and calculate and obtain the 3D coordinates of the object to be measured.

[0029] The calibration and reconstruction method of the three-dimensional measurement system of the present invention uses orthogonal bidirectional phase information to track the corresponding light of each pixel of the imaging device in the measurement space to calibrate the light corresponding to each pixel of the imaging device. It only needs to determine the light equation corresponding to each pixel within the imaging depth of field, without considering the structural layout of the imaging system, avoiding the complex process of strictly analyzing and establishing each imaging model, and also avoiding the accuracy loss caused by the approximate expression of lens distortion; by associating the light corresponding to the pixel of the imaging device with the phase of the projection, the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target of each posture are determined, the phase mapping coefficient of the pixel light of the imaging device is fitted, and a lookup table of the phase mapping coefficient of the pixel light of the imaging device is established, and the phase value of the surface of the measured object is obtained according to the image of the measured object after the projection pattern is acquired by the imaging device. In combination with the lookup table, the corresponding phase mapping coefficient is obtained to directly calculate the three-dimensional coordinates of the measured object, thereby improving the three-dimensional measurement efficiency, having the potential for high-precision calibration of different types of fringe projection systems, without the need to calibrate the internal parameters of the three-dimensional measurement system, without the need to approximate the lens distortion, and having higher calibration accuracy and three-dimensional reconstruction accuracy, simple operation, and strong versatility.

[0030] Combination Figure 2 Specifically, the step S110 includes:

[0031] Step S111, placing the display in a plurality of positions in a measurement space in sequence in different postures, the display displays an orthogonal two-way phase-shifted fringe pattern at each position, and the imaging device collects and obtains the orthogonal two-way fringe image of the display in each posture. Among them, the orthogonal two-way fringe image refers to the image obtained after the display in each posture collected by the imaging device displays the orthogonal two-way phase-shifted fringe pattern. The phase information of the orthogonal two-way direction can be calculated and obtained according to the orthogonal two-way fringe image of the display in each posture collected and obtained by the imaging device in combination with the phase shift method. The display is a phase target for the light calibration of each pixel of the imaging device, and by displaying the orthogonal two-way phase-shifted fringe pattern, a reference plane encoded with phase information is formed, so that the position of the spatial point on the display can be directly located by the phase information, without the need to calculate the absolute phase by the interpolation method, thereby improving the efficiency of the light calibration of the pixels of the imaging device. The display is moved back and forth in the measurement space in sequence in different postures to a plurality of positions to ensure the accuracy of the light calibration. The display can be an LCD display.

[0032] Step S112, determine the corresponding point of the intersection of the light of each pixel of the imaging device and the display of each posture on the display plane of the display, minimize the distance between the intersection of the light corresponding to each pixel of the imaging device and the display of each posture and the spatial point of the intersection in the light coordinate system, construct a first function, calculate and obtain the posture parameters of the display of each posture, and calibrate the parameters of the light of each pixel of the imaging device.

[0033] Among them, the light corresponding to any pixel of the imaging device intersects with the display in the measurement space, and the three-dimensional coordinates of the corresponding points on the display plane of the display of the intersection point of the light corresponding to each pixel of the imaging device and the display of each posture can be obtained by the orthogonal two-directional phase of the pixel of the imaging device itself, and the orthogonal two-directional phase of the pixel of the imaging device itself can be calculated based on the orthogonal two-directional fringe image of the display of each posture acquired by the imaging device combined with the phase shift method. The corresponding points on the display plane of the display of the intersection point of the light of each pixel of the imaging device and the display of each posture can be expressed by the following formula:

[0034]

[0035] In the formula, Represents the corresponding point on the display plane of the display where the light corresponding to each pixel of the imaging device intersects with the display at each posture, ij represents the index of the pixel, i and j are the serial numbers of the pixel in the row and column respectively, N represents the index of the display at different postures, and the superscript L represents the display.

[0036] The spatial point of the intersection of the light of each pixel of the imaging device and the display of each posture in the light coordinate system can be calculated using the following formula:

[0037]

[0038] In the formula, The spatial point in the light coordinate system where the light corresponding to each pixel of the imaging device intersects with the display at each position, The corresponding point on the display plane of the display where the light corresponding to each pixel of the imaging device intersects with the display at each position, ij represents the index of the pixel, i and j are the serial numbers of the pixel in the row and column respectively, N represents the index of the display at different positions, and the superscript L represents the display. The rigid body transformation matrix of the display in the Nth position is used to describe the conversion between coordinate systems. The rotation matrix of the display in the Nth pose relative to the light coordinate system, The translation matrix of the display in the Nth position relative to the light coordinate system is represented, wherein the light coordinate system refers to the coordinate system where any point on the light of the pixel of the imaging device is located.

[0039] Minimize the distance between the intersection of the light corresponding to each pixel of the imaging device and the display of each posture and the spatial point of the intersection in the light coordinate system, and construct a first loss function to calibrate the parameters of the light corresponding to each pixel of the imaging device. The key to calibrating the parameters of the light is to determine the posture parameters corresponding to the display of each posture, and use the straight line constraint of the light to construct the first loss function to calculate the optimal posture parameters of the display of each posture. The first loss function can be expressed by the following formula:

[0040]

[0041] Where f1 represents the first loss function, τ represents the pose parameters of the N displays involved in the optimization, The spatial point in the ray coordinate system representing the intersection of the ray of each pixel of the imaging device and the display at each position, The light and posture parameters corresponding to each pixel of the imaging device are represented as The intersection of the display, ij represents the index of the pixel, i and j are the serial numbers of the pixel in the row and column respectively, N represents the index of the display in different postures, and the superscript L represents the display.

[0042] Ideally, when the posture parameters of the display are correct, the intersection of the light corresponding to each pixel of the imaging device and the display at each posture coincides with the spatial point of the intersection in the light coordinate system. Then, the distance between the intersection of the light corresponding to each pixel of the imaging device and the display at each posture and the spatial point of the intersection in the light coordinate system is zero, that is,

[0043] Combined with the optimal posture parameters of the display for each posture calculated according to the first loss function, the spatial point of the intersection of the light corresponding to each pixel of the imaging device and the display for the posture corresponding to the optimal posture parameters is obtained in the light coordinate system, and the light corresponding to each pixel of the imaging device is calibrated.

[0044] Combination Figure 3 , the step S120 specifically includes:

[0045] Step S121, placing the projection receiving plane target in a plurality of positions in the measurement space in different postures, a projector projects a unidirectional phase-shifted fringe pattern to the projection receiving plane target in each posture, and an imaging device collects and acquires the projection image of the projection receiving plane target in each posture.

[0046] Step S122, minimize the distance between the intersection of the light of the image point of each reference point and the projection receiving plane target of each pose and the spatial point of each reference point of the projection receiving plane target of each pose in the light coordinate system, construct a second loss function, and calculate and obtain the optimal posture parameters of the projection receiving plane target of each pose.

[0047] Among them, the reference points of the projection receiving plane target are calibrated in advance, and the coordinates of the target surface of each reference point on the projection receiving plane target at each posture are expressed by the following formula:

[0048]

[0049] Wherein, the superscript w represents the projection receiving plane target, m represents the serial number of the reference point, and the superscript T represents transposition. Represents the coordinates of the mth reference point on the target surface of the projection receiving plane target.

[0050] The spatial points of each reference point of the projection receiving plane target in each posture in the light coordinate system can be calculated using the following formula:

[0051]

[0052] Where m represents the index of the reference point, k represents the index of the projection receiving plane target at different positions, and the superscript w represents the projection receiving plane target. Represents the spatial point of the mth reference point of the projection receiving plane target of the kth pose in the light coordinate system, Represents the coordinates of the target surface of the projection receiving plane target of the mth reference point at the kth position, Represents the rigid body transformation matrix of the projected receiving plane target at the k-th pose, which is used to describe the conversion between coordinate systems. Represents the rotation matrix of the projection receiving plane target of the kth pose relative to the light coordinate system, Represents the translation matrix of the projected receiving plane target of the kth pose relative to the light coordinate system.

[0053] The second loss function can be expressed as follows:

[0054]

[0055] Where f2 represents the second loss function, τ′ represents the pose parameters of the K projected receiving plane targets involved in the optimization, m represents the serial number of the reference point, M represents the total number of reference points, k represents the index of the projection receiving plane target in different positions, K represents the total number of times the projection receiving plane target moves, is the index of the projection receiving plane target in different positions, and the superscript w represents the projection receiving plane target. Represents the spatial points of each reference point of the projection receiving plane target in each posture in the light coordinate system, The light and pose parameters representing the image points of each reference point are The intersection of the projection receiving plane target, The projection receiving plane target at each position represents the light corresponding to the image point of each reference point.

[0056] Combined with the optimal posture parameters of the projection receiving plane target in each posture calculated according to the second loss function, the spatial point of the reference point of the projection receiving plane target in the posture corresponding to the optimal posture parameters in the light coordinate system is obtained.

[0057] The plane parameters of the projected receiving plane target in the camera coordinate system are calculated according to the following formula:

[0058]

[0059] In the formula, represents the plane parameters of the projected receiving plane target of the kth pose in the measurement space in the camera coordinate system, and the subscript c represents the camera coordinate system. Represents the plane parameters of the projected receiving plane target of the kth pose in the measurement space in the world coordinate system, where H- T Represents the inverse transpose of the rigid body transformation matrix between the camera coordinate system and the world coordinate system, The third column vector of the rotation matrix R of the projected receiving plane target of the k-th pose in the measurement space, where the superscript T indicates transposition, t k represents the external parameter of the projected receiving plane target of the kth pose in the measurement space in the camera coordinate system, r3 k The third column number of the rotation matrix R of the projected receiving plane target representing the k-th pose in the measurement space.

[0060] The spatial plane parameters of the projection receiving plane target obtained by calculation are used to calculate the three-dimensional coordinates of the spatial point in the light coordinate system of the intersection of the light corresponding to each pixel of the imaging device and the projection receiving plane target of each posture.

[0061] Combination Figure 4 , the step 150 specifically includes:

[0062] Step S151, a projector projects a unidirectional phase-shifted fringe pattern onto the surface of the object to be measured, and a phase value of the surface of the object to be measured is calculated using a phase shift method based on an image of the object to be measured after the unidirectional phase-shifted fringe pattern is projected and acquired by an imaging device.

[0063] Step S152: According to the obtained phase value of the surface of the measured object, in combination with a lookup table, a phase mapping coefficient corresponding to the phase value of the surface of the measured object is obtained.

[0064] Step S153: Calculate the three-dimensional coordinates of the object under test according to the obtained phase value and the corresponding phase mapping coefficient.

[0065] The mapping relationship between the depth and phase of a point on the light in the projector coordinate system can be expressed by the following formula:

[0066]

[0067] In the formula, c n Represents the phase mapping coefficient, representing the depth, represents the phase, the subscript p represents the projector coordinate system, and N represents the polynomial order, n∈N.

[0068] According to formula (9) combined with formula (1), the coordinates of the point on the light in the projector coordinate system can be calculated, and then the three-dimensional coordinates of the space point corresponding to the point in the light coordinate system can be obtained by coordinate system conversion, thereby obtaining the three-dimensional coordinates of the object to be measured.

[0069] See also Figure 5 , Figure 5 is a schematic block diagram of a three-dimensional measurement system provided by an embodiment of the present invention, such as Figure 5As shown, the three-dimensional measurement system 10 includes an imaging device 11, a display 12, a projector 13 and a projection receiving plane target 14, wherein the imaging device 11 is used to collect images, and the projector 13 is used to project a unidirectional phase-shifted fringe pattern, wherein the area at the junction of the clearly focused field of view of the imaging device 11 and the clear projection area of ​​the projector 13 forms a measurement space; the display 12 is arranged in the measurement space, and is used to display orthogonal bidirectional phase-shifted fringe patterns, and the projection receiving plane target 14 is arranged in the measurement space, and is used to project the unidirectional phase-shifted fringe pattern projected by the projector 13, and the projection receiving plane target 14 adopts a white-bottomed plane plate printed with multiple reference points. The arrows in the figure are the directions of information transmission.

[0070] The three-dimensional measurement system of the present invention forms a measurement space by arranging a display for displaying an orthogonal two-way phase-shifted fringe pattern in the area at the junction of the clearly focused field of view of the imaging device and the clear projection area of ​​the projector, moving the display back and forth to multiple positions in different postures and using the imaging device to collect and obtain the corresponding orthogonal two-way fringe image, so as to track the corresponding light of each pixel of the imaging device in the measurement space by using the orthogonal two-way phase information to calibrate the light corresponding to each pixel of the imaging device; a white-bottomed flat plate printed with multiple reference points is used as a projection receiving flat target to replace the display, and the imaging device collects the corresponding image in conjunction with the unidirectional phase-shifted fringe pattern projected by the projector to compare the light corresponding to the pixel of the imaging device with the phase of the projection. The method is to associate the light of each pixel of the imaging device with the projection receiving plane target of each posture to determine the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target, fit the phase mapping coefficient of the pixel light of the imaging device, establish a lookup table for storing the phase mapping coefficient of the pixel light of the imaging device, obtain the phase value of the surface of the measured object according to the image of the measured object after the projection pattern acquired by the imaging device, and obtain the corresponding phase mapping coefficient in combination with the lookup table to directly calculate the three-dimensional coordinates of the measured object, thereby improving the efficiency of three-dimensional measurement, having the potential for high-precision calibration of different types of fringe projection systems, without the need to calibrate the internal parameters of the three-dimensional measurement system, without the need to approximate the lens distortion, and having higher calibration accuracy and three-dimensional reconstruction accuracy, and having strong versatility.

[0071] Preferably, the display 11 may be an LCD display.

[0072] In summary, the calibration and reconstruction method of the three-dimensional measurement system of the present invention tracks the corresponding light of each pixel of the imaging device in the measurement space by using the phase information of orthogonal two directions to calibrate the light corresponding to each pixel of the imaging device. It only needs to determine the light equation corresponding to each pixel within the imaging depth of field, without considering the structural layout of the imaging system, avoiding the complex process of strictly analyzing and establishing each imaging model, and also avoiding the accuracy loss caused by the approximate expression of lens distortion; by associating the light corresponding to the pixel of the imaging device with the phase of the projection, so as to determine the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target of each posture, the phase mapping coefficient of the pixel light of the imaging device is fitted, and a lookup table for storing the phase mapping coefficient of the pixel light of the imaging device is established. The phase value of the surface of the measured object is obtained according to the image of the measured object after the projection pattern is acquired by the imaging device. In combination with the lookup table, the corresponding phase mapping coefficient is obtained to directly calculate the three-dimensional coordinates of the measured object, thereby improving the three-dimensional measurement efficiency, having the potential for high-precision calibration of different types of fringe projection systems, without the need to calibrate the internal parameters of the three-dimensional measurement system, without the need to approximate the lens distortion, and having higher calibration accuracy and three-dimensional reconstruction accuracy, and strong versatility. The three-dimensional measuring system of the present invention also has the above-mentioned functions.

[0073] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A calibration and reconstruction method for a three-dimensional measurement system, characterized in that: The following steps are involved: Imaging device pixel light calibration: Use the phase information in orthogonal two directions to track the corresponding light of each pixel of the imaging device in the measurement space, and construct a first loss function to calibrate the light parameters; wherein the orthogonal two directions refer to the horizontal and vertical directions, and the measurement space is the area at the junction of the imaging device's clearly focused field of view and the projector's clearly projected area; Correlate the pixel light of the imaging device with the projection phase: use a white-bottom plane plate printed with multiple reference points as a projection receiving plane target, place the projection receiving plane target in multiple positions in the measurement space in different postures, project a unidirectional phase-shifted fringe pattern to the projection receiving plane target at each posture, and collect and obtain the projection image of the projection receiving plane target at each posture of the imaging device, construct a second loss function, and calculate and obtain the posture parameters of the projection receiving plane target at each posture; Fitting the phase mapping coefficient of the pixel light of the imaging device: determining the three-dimensional coordinates and phase of the intersection of the light of each pixel of the imaging device and the projection receiving plane target of each posture, and fitting the phase mapping coefficient of the pixel light of the imaging device; Establishing a lookup table: establishing a lookup table storing phase mapping coefficients of pixel light of an imaging device; Three-dimensional reconstruction: Project a unidirectional phase-shifted fringe pattern onto the object to be measured, obtain the phase value of the surface of the object to be measured, combine with the lookup table to obtain the phase mapping coefficient corresponding to the phase value of the surface of the object to be measured, and calculate the three-dimensional coordinates of the object to be measured.

2. The calibration and reconstruction method of a three-dimensional measurement system according to claim 1, characterized in that: The step of calibrating the pixel light of the imaging device specifically includes the following steps: The display is sequentially placed in a plurality of positions in a measurement space in different postures, and the display displays an orthogonal bidirectional phase-shifted fringe pattern at each position, and an imaging device collects and obtains the orthogonal bidirectional fringe image of the display at each posture; Determine the corresponding point of the intersection of the light of each pixel of the imaging device and the display of each posture on the display plane of the display, minimize the distance between the intersection of the light corresponding to each pixel of the imaging device and the display of each posture and the spatial point of the intersection in the light coordinate system, construct a first function, calculate and obtain the posture parameters of the display of each posture, and calibrate the parameters of the light of each pixel of the imaging device.

3. The calibration and reconstruction method of a three-dimensional measurement system according to claim 1, characterized in that: The three-dimensional reconstruction step specifically includes: The projector projects a unidirectional phase-shifted fringe pattern onto the surface of the object to be measured, and the phase value of the surface of the object to be measured is calculated by using a phase shift method according to the image of the object to be measured after the unidirectional phase-shifted fringe pattern is projected and acquired by the imaging device; According to the obtained phase value of the surface of the measured object, in combination with the lookup table, a phase mapping coefficient corresponding to the phase value of the surface of the measured object is obtained; The three-dimensional coordinates of the object under test are calculated based on the obtained phase value and the corresponding phase mapping coefficient.

4. The calibration and reconstruction method of a three-dimensional measurement system according to claim 1, characterized in that: The step of associating the pixel light of the imaging device with the projection phase specifically includes: The projection receiving plane target is placed in a plurality of positions in the measurement space in different postures, a projector projects a unidirectional phase-shifted fringe pattern to the projection receiving plane target in each posture, and an imaging device collects and obtains the projection image of the projection receiving plane target in each posture; Minimize the distance between the intersection of the light of the image point of each reference point and the projection receiving plane target of each pose and the spatial point of each reference point of the projection receiving plane target of each pose in the light coordinate system, construct the second loss function, and calculate the optimal posture parameters of the projection receiving plane target of each pose.

5. A three-dimensional measurement system, applicable to the calibration and reconstruction method of the three-dimensional measurement system according to claim 1, characterized in that: include: An imaging device, for collecting images; a projector for projecting a unidirectional phase-shifted fringe pattern, wherein an area at the junction of a clearly focused field of view of the imaging device and a clearly projected area of ​​the projector forms a measurement space; A display, disposed in the measurement space, for displaying orthogonal bidirectional phase-shifted fringe patterns; The projection receiving plane target is arranged in the measuring space and is used for projecting the unidirectional phase shift fringe pattern projected by the projector. The projection receiving plane target adopts a white bottom plane plate printed with a plurality of reference points.

6. The three-dimensional measurement system according to claim 5, characterized in that: The display is an LCD display.

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