Coordinate system plane calibration method and system applied to 2D-PIV

Abstract

The invention discloses a coordinate system plane calibration method and system applied to 2D-PIV, and the method comprises the following steps: determining the position of laser light source equipment, recording the irradiation direction of a sheet light source emitted by the light source equipment as a first direction, and recording the direction perpendicular to the irradiation direction of the sheet light source as a second direction; the preset calibration plate is placed at a position A with a preset distance from the light source equipment in the irradiation direction of the sheet light source, and a deflection angle theta is formed between the preset calibration plate and the plane where the sheet light source is located; enabling the preset calibration plate to move relative to the light source equipment in a direction parallel to the second direction; for the irradiated calibration plate at different moments in the moving process, a camera is used for collecting calibration plate images, the calibration plate images have areas illuminated by a sheet light source, and multiple calibration plate images at different moments are obtained; and based on the calibration plate image, analyzing calibration parameters of the camera. Compared with an existing design operation which depends on human eyes to judge that the laser plane coincides with the calibration plate, the method has the advantages that errors during measurement are reduced, and an additional plane self-calibration process does not need to be carried out.

Description

Technical Field

[0001] The present invention belongs to the technical field of image processing, and particularly relates to a coordinate system plane calibration method and system applied to 2D-PIV. Background Art

[0002] 2D-PIV uses a sheet light source to illuminate particles in a fluid, and then calculates the velocity field of the fluid by using the motion of the illuminated particles. During the calibration process of 2D-PIV, the requirement for placing the calibration plate is that the calibration plate coincides with the laser plane. Then, under this condition, an image of the calibration plate is taken. When taking the image of the calibration plate, the calibration plate needs to be illuminated by a laser light source with the same wavelength. At this time, the position of the laser light source is different from that of the light source finally used for particle velocity measurement. Therefore, generally, an additional light source is used to complete this, and finally, the plane where the calibration plate is located is used as the XOY plane of the world coordinate system. In the calculation process of 2D3C-PIV, it highly depends on the position of the calibrated XOY plane, and finally, the calculated velocity components are decomposed into in-plane velocity components and velocity components perpendicular to the plane.

[0003] However, in actual operation, it is very difficult to ensure that the laser plane completely coincides with the calibration plate. Basically, it can only rely on human eye judgment, which will bring errors in measurement. Especially for the 2D3C scenario, the 2D3C scenario requires an additional plane self-calibration process using the particle image to correct the non-coincidence between the laser plane and the calibration plate. Aiming at the deficiencies of the existing technology, it is urgently necessary to design a coordinate system plane calibration method and system applied to 2D-PIV to solve the above technical problems. Summary of the Invention

[0004] To solve the deficiencies in the above-mentioned existing technology, the purpose of the present invention is to overcome the existing deficiencies and provide a coordinate system plane calibration method applied to 2D-PIV. The method includes the following steps:

[0005] Determine the position of the laser light source device. Denote the irradiation direction of the sheet light source emitted by the light source device as the first direction, and denote the direction perpendicular to the irradiation direction of the sheet light source as the second direction;

[0006] Place the preset calibration plate at position A at a preset distance from the light source device in the irradiation direction of the sheet light source, and the preset calibration plate has a deflection angle θ with the plane where the sheet light source is located;

[0007] Relatively move the preset calibration plate and the light source device in the direction parallel to the second direction;

[0008] For the calibration plate irradiated by the sheet light source at different moments during the movement process, use a camera to collect images of the calibration plate. The calibration plate image has an area illuminated by the sheet light source, and obtain multiple calibration plate images at different moments; the shooting direction of the camera is on the same straight line as the relative movement direction of the calibration plate.

[0009] Analyze the calibration parameters of the camera based on multiple calibration board images at different times.

[0010] As a further optimization of the above solution, the relative movement of the preset calibration board and the light source device in the direction parallel to the second direction includes: translating the preset calibration board along the direction parallel to the second direction while keeping the position of the light source device unchanged, or translating the position of the light source device along the second direction while keeping the position of the preset calibration board unchanged, so that the preset calibration board and the light source device move relative to each other in the direction parallel to the second direction.

[0011] As a further optimization of the above solution, construct a laser plane coordinate system XOY based on the plane where the sheet light source is located. The specific method includes the following:

[0012] Set the coordinates of any feature point of the laser plane coordinate system XOY as (X i , Y i ), and the (X i , Y i ) are experimental group data;

[0013] Let the distance between the circular areas of the calibration board be s, then X i = X0 + n * s * cosθ, Y i = Y0 + m * s, where (m, n) represents the row number and column number of the feature point on the calibration board, and X0 and Y0 are constants.

[0014] As a further optimization of the above solution, construct a coordinate system plane for describing the calibration board image based on the laser plane coordinate system XOY, including the following:

[0015] Based on the generated calibration board image, obtain the pixel coordinates (u i , v i ) corresponding to the coordinates of any feature point (X i , Y i ) of the laser plane coordinate system XOY in the calibration board image. The (u i , v i ) are experimental group data;

[0016] Then:

[0017]

[0018] Repeat the above steps to obtain the coordinates of N feature points of the laser plane coordinate system XOY and the corresponding pixel coordinates of the calibration board image. Based on Equation (1), then:

[0019]

[0020] Among them, is a projection matrix;

[0021] Based on the above formula and the experimental group data, the camera parameter values of the projection matrix are calculated and obtained.

[0022] As a further optimization of the above solution, the calibration board is set as follows:

[0023] The calibration board includes multiple horizontal bars, and the multiple horizontal bars have the same width; the midline positions of the multiple horizontal bars include multiple circular regions with equal intervals and sizes.

[0024] As a further optimization of the above solution, the calibration board is set as follows: The multiple horizontal bars are in the same plane, forming a planar calibration board.

[0025] As a further optimization of the above solution, the calibration board is set as follows:

[0026] The calibration board includes multiple horizontal bars, which are divided into multiple first horizontal bars and second horizontal bars. The first horizontal bars and the second horizontal bars have the same width and are arranged at intervals; any first horizontal bar is higher than any second horizontal bar, and the corresponding height distance is h; the midline positions of all the horizontal bars include multiple circular regions with equal intervals and sizes.

[0027] As a further optimization of the above solution, the calibration board is set as follows: All the circular regions distributed on the first horizontal bars are in the same plane, denoted as the first plane, and are arranged in a matrix. The rectangular area formed by any four adjacent circular regions on the first plane is equal; all the circular regions distributed on the second horizontal bars are in the same plane, denoted as the second plane, and are arranged in a matrix. The rectangular area formed by any four adjacent circular regions on the second plane is equal.

[0028] As a further optimization of the above solution, the calibration board is set as follows: The rectangular area formed by any four adjacent circular regions on the calibration board is equal.

[0029] The present invention also discloses a coordinate system plane calibration system for 2D-PIV based on the above description. The system includes the following:

[0030] A calibration board, which is used to reflect the received light;

[0031] A laser device, which is used to emit laser light to the calibration board to generate a bright area. The angle formed by the laser emission direction of the laser device and the calibration board is θ;

[0032] A camera, which is used to collect the image of the bright area generated by emitting laser light to the calibration board in real time. The angle formed by the camera shooting direction and the laser emission direction of the laser device is 90°.

[0033] The present invention adopts the above technical solution, and compared with the prior art, has the following beneficial effects:

[0034] By designing a coordinate system plane calibration system applied to 2D-PIV, a sheet light source is used to irradiate an inclined calibration plate, and then the calibration plate moves in a direction perpendicular to the sheet light source. Each time it moves, an image of the area of the calibration plate illuminated by the laser plane is obtained. By superimposing multiple groups of images, a complete calibration plate image can be obtained. The XOY plane of the coordinate system established after calibration using this image is ensured to coincide with the laser plane. Compared with the existing design operation that relies on the human eye to judge the coincidence of the laser plane and the calibration plate, this method greatly reduces the error during measurement and does not require the additional process of plane self-calibration using particle diagrams in the 2D3C scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present application will become more apparent:

[0036] Figure 1 is a schematic flow chart of the present invention;

[0037] Figure 2 is a schematic system diagram of the present invention;

[0038] Figure 3 is another schematic system diagram of the present invention;

[0039] Figure 4 is a schematic diagram of image accumulation of the present invention;

[0040] Figure 5 is a schematic diagram of an embodiment of the calibration plate structure of the present invention, where (a)-(d) are different views of the calibration plate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] As Figures 1-5 shown, the embodiment of the present invention discloses a coordinate system plane calibration method applied to 2D-PIV, which specifically includes the following steps:

[0043] Determine the position of the laser light source device, record the irradiation direction of the sheet light source emitted by the light source device as the first direction, and record the direction perpendicular to the irradiation direction of the sheet light source as the second direction;

[0044] Place a preset calibration plate at position A at a preset distance from the light source device in the irradiation direction of the sheet light source, and the preset calibration plate has a deflection angle θ with the plane where the sheet light source is located;

[0045] Move a preset calibration board relative to the light source device in a direction parallel to the second direction;

[0046] For the calibration board illuminated by the sheet light source at different moments during the movement, use a camera to collect calibration board images. There is an area illuminated by the sheet light source in the calibration board images, and obtain multiple calibration board images at different moments; the shooting direction of the camera and the relative movement direction of the calibration board are on the same straight line; the calibration board of the present invention moves uniformly along the same straight line direction as the image of the collected bright area. Since the light emitted by the laser forms a bright spot stripe on the calibration board, when taking the image of the bright area, by placing a narrow-band filter with the same wavelength as the laser light source, the interference of other surrounding image contents is reduced. Finally, the obtained bright area is processed into an image where it is bright through a circular area and dark otherwise; when multiple such images are accumulated, a complete spot image can be obtained.

[0047] Analyze the calibration parameters of the camera based on multiple calibration board images at different moments.

[0048] This invention patent designs a coordinate system plane calibration method applied to 2D-PIV. The sheet light source irradiates on an inclined calibration board, and then the calibration board moves along the direction perpendicular to the sheet light source. Each time it moves, an image of the area illuminated by the laser plane on the calibration board is obtained. Stacking multiple groups of images can obtain a complete calibration board image. Using the coordinate system established after calibration with this image, its XOY plane is ensured to coincide with the laser plane. Compared with the existing design operation that relies on the human eye to judge the coincidence of the laser plane and the calibration board, this method greatly reduces the error during measurement and does not require the additional process of plane self-calibration using particle diagrams in the 2D3C scenario.

[0049] Specifically, translate the preset calibration board along the direction parallel to the second direction while keeping the position of the light source device fixed, or translate the position of the light source device along the second direction while keeping the position of the preset calibration board fixed, so that the preset calibration board moves relative to the light source device in a direction parallel to the second direction.

[0050] More specifically, the calibration board is placed vertically on the platform in the horizontal direction of the horizontal bar. The acute angle formed by the calibration board and the laser emission plane is θ; by setting the inclination angle, the light emitted by the laser can be easily captured, and the bright area on the calibration board must be the laser plane, which is convenient for accurately capturing the scanned image of the laser plane.

[0051] Specifically, construct a laser plane coordinate system XOY based on the plane where the sheet light source is located. The specific method includes the following:

[0052] Set the coordinates of any feature point of the laser plane coordinate system XOY as (X i , Y i ), (Xi , Y i ) are the experimental group data; it should be particularly noted that in the embodiments of the present invention, when referring to (X i , Y i ), (u i , v i ) are the experimental group data, which means that during the calibration process of the 2D-PIV coordinate system plane, the research values measured by known means or technical solutions are used. By calculating the numerical relationship, an accurate laser plane coordinate system XOY is obtained for further research;

[0053] Let the distance between the circular regions of the calibration plate be s, then X i = X0 + n * s * cosθ, Y i = Y0 + m * s, where (m, n) represents the row number and column number of the feature point on the calibration plate, and X0 and Y0 are constants; more specifically, X0 and Y0 are related to the selection of the origin of the XOY coordinate system and are the basic distances from the feature point to the origin of the XOY coordinate system; it should be particularly noted that for the convenience of calculation in the embodiments of the present invention, it is preferably designed that the distances between the circular regions of the calibration plate are equal. In the actual application process, it can be designed to have equal distances horizontally and vertically respectively. For example, if the horizontal distance between the feature points of the calibration plate is w and the vertical distance is t, then X i = X0 + n * w * cosθ, Y i = Y0 + m * t.

[0054] Specifically, the method for constructing the coordinate system plane based on the calibration plate image further includes the following:

[0055] Based on the generated calibration plate image, the pixel coordinates (u i , v i ) corresponding to any feature point coordinates (X i , Y i ) of the laser plane coordinate system XOY are obtained, and (u u , v i ) are the experimental group data;

[0056] Then:

[0057]

[0058] Repeat the above steps to obtain the feature point coordinates of N laser plane coordinate systems XOY and the corresponding pixel coordinates of the calibration plate image. Based on Equation (1), then there is:

[0059]

[0060] Among them, is the projection matrix;

[0061] Based on the above formula and the experimental group data, the camera parameter values of the projection matrix are calculated and obtained.

[0062] More specifically, the present invention first detects and obtains the coordinates of any feature point in the laser plane coordinate system XOY and its corresponding pixel coordinates of the calibration plate image through the experimental group data. By applying this set of control points, the conversion relationship between the laser plane coordinate system and the pixel coordinate system is obtained, that is, the acquisition of the projection matrix; then, through the projection matrix, the relational expression of any feature point between the laser plane coordinate system and the pixel coordinate system is constructed, so that the coordinate value of the corresponding laser plane coordinate system can be easily obtained through the pixel coordinate system, and multiple groups of feature points are applied to complete the accurate calibration of this plane.

[0063] Specifically, the calibration plate is set as follows: the calibration plate includes multiple horizontal stripes with equal widths; the midline positions of the multiple horizontal stripes include multiple circular regions with equal intervals and sizes;

[0064] For the shape of the calibration plate, the present invention provides an implementation manner. The calibration plate is set as follows: multiple horizontal stripes are in the same plane, forming a planar calibration plate. Specifically, the calibration plate of the present invention is a planar calibration plate with multiple circular regions distributed and presented as a matrix, such as the checkerboard calibration plate in the conventional technology.

[0065] For the shape of the calibration plate, the present invention provides another embodiment. The calibration plate includes multiple horizontal stripes, which are divided into multiple first horizontal stripes and second horizontal stripes. The first horizontal stripes and the second horizontal stripes have equal widths and are arranged at intervals; any first horizontal stripe is higher than any second horizontal stripe, and the corresponding height distance is h; the midline positions of all horizontal stripes include multiple circular regions with equal intervals and sizes.

[0066] For the distribution of the circular regions on the calibration plate, the present invention provides an implementation manner (as Figure 5 shown), all the circular regions distributed on the first horizontal stripe are in the same plane, denoted as the first plane. All the circular regions on the first plane are regularly arranged in a matrix, and the rectangular area formed by any four adjacent circular regions on the first plane is equal; all the circular regions distributed on the second horizontal stripe are in the same plane, denoted as the second plane. All the circular regions on the second plane are arranged in a matrix, and the rectangular area formed by any four adjacent circular regions on the second plane is equal. In this embodiment, the applied calibration plate is a three-dimensional integrated structure, with two feature points of different heights on the same surface; specifically, the two different heights are the height difference between the parallel positions of the first horizontal stripe and the second horizontal stripe, denoted as h; and multiple first horizontal stripes and second horizontal stripes are arranged alternately. When viewing the calibration plate from the front, the calibration plate has multiple horizontal stripes, and each horizontal stripe has circular regions at equal intervals. The circular regions of each adjacent two horizontal stripes are equally spaced and staggered, and there are corresponding feature point coordinates between the two different heights. and There is the following relationship X i′ = X i + h·cosθ; Based on the calibration detection of the double-layer calibration plate, the calibration of the two-layer laser plane coordinate system is applied, which further improves the calibration accuracy of the technical solution of the present invention. In addition, in this embodiment, based on the setting that the first horizontal bar and the second horizontal bar on the calibration plate are not in the same plane, it is also possible to determine the parallel position height difference between the first horizontal bar and the second horizontal bar in the image when the calibration plate is set parallel to the camera acquisition direction (such as Figure 5 (c)) and the height difference between the first horizontal bar and the second horizontal bar in the image when the calibration plate is set obliquely with respect to the camera acquisition direction (such as Figure 5 (d)) to analyze the tilt angle of the calibration plate.

[0067] For the distribution of the circular regions on the calibration plate, the present invention provides another implementation manner. The rectangular area formed by any four adjacent circular regions among all the circular regions on the calibration plate is equal. More specifically, any four adjacent circular regions can be regarded as the four vertices of a rectangle, including two cases where multiple horizontal bars are in the same plane and not in the same plane.

[0068] It should be noted that an embodiment of the present invention is a coordinate system plane calibration system applied to 2D-PIV, and its implementation technical means are the same as those of the coordinate system plane calibration method applied to 2D-PIV, so it will not be elaborated here.

[0069] It should be noted that in this article, the terms "including", "comprising" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including that element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, the features described with reference to certain examples may be combined in other examples.

[0070] Through the description of the above embodiments, those skilled in the art can clearly understand that the above-described embodiment methods can be implemented by means of software plus a necessary general hardware platform. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art can be embodied in the form of a computer software product. The computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions for causing a terminal (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods of various embodiments of the present application.

[0071] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific implementation manners. The above specific implementation manners are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all of them belong to the protection scope of the present application.

[0072] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0073] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present application. The scope of the present application is defined by the claims and their equivalents.

Claims

1. A coordinate system plane calibration method applied to 2D-PIV, characterized in that The method includes the following steps: Determine the position of the laser light source device. Denote the irradiation direction of the sheet light source emitted by the light source device as the first direction, and denote the direction perpendicular to the irradiation direction of the sheet light source as the second direction; Place a preset calibration plate at position A at a preset distance from the light source device in the irradiation direction of the sheet light source, and the preset calibration plate has a deflection angle θ with the plane where the sheet light source is located; Relatively move the preset calibration plate and the light source device in a direction parallel to the second direction; For the calibration plate irradiated by the sheet light source at different moments during the movement, use a camera to collect calibration plate images. There is an area illuminated by the sheet light source in the calibration plate images, and obtain multiple calibration plate images at different moments; the shooting direction of the camera and the direction of relative movement of the calibration plate are on the same straight line; Analyze the calibration parameters of the camera based on multiple calibration plate images at different moments.

2. The coordinate system plane calibration method applied to 2D-PIV according to claim 1, characterized in that The relatively moving the preset calibration plate and the light source device in a direction parallel to the second direction includes: translating the preset calibration plate along a direction parallel to the second direction while keeping the position of the light source device unchanged, or translating the position of the light source device along the second direction while keeping the position of the preset calibration plate unchanged, so that the preset calibration plate and the light source device relatively move in a direction parallel to the second direction.

3. The coordinate system plane calibration method applied to 2D-PIV according to claim 1, characterized in that, Construct a laser plane coordinate system XOY based on the plane where the sheet light source is located. The specific method includes the following: Set the coordinates of any feature point in the laser plane coordinate system XOY as (X i , Y i ), and the (X i , Y i ) are the experimental group data; Let the spacing between the circular regions of the calibration board be s, then X i = X0 + n * s * cosθ, Y i = Y0 + m * s, where (m, n) represents the row number and column number of the feature point on the calibration board, and X0 and Y0 are constants.

4. A coordinate system plane calibration method for 2D-PIV according to claim 3, characterized in that Construct a coordinate system plane for describing the calibration plate image based on the laser plane coordinate system XOY, including the following: Based on the generated calibration board image, obtain the coordinates (X i , Y i ) of any feature point in the laser plane coordinate system XOY. The pixel coordinates of the corresponding calibration board image are (u i , v i ), and the (u i , v i ) are the experimental group data; Then: Repeat the above steps to obtain the coordinate values of the feature points of N laser plane coordinate systems XOY and the pixel coordinates of the corresponding calibration plate images. Based on Equation (1), then: wherein, is a projection matrix; Calculate the values of each camera parameter of the projection matrix based on the above formula and the experimental group data.

5. A coordinate system plane calibration method applied to 2D-PIV according to claim 4, characterized in that The calibration plate is set as follows: The calibration plate includes multiple horizontal bars, and the multiple horizontal bars have the same width; the midline positions of the multiple horizontal bars include multiple circular regions with equal intervals and sizes.

6. A coordinate system plane calibration method for 2D-PIV according to claim 5, characterized in that, The calibration plate is set as follows: The multiple horizontal bars are in the same plane, forming a planar calibration plate.

7. A coordinate system plane calibration method for 2D-PIV according to claim 5, characterized in that The calibration plate is set as follows: The calibration plate includes multiple horizontal bars, which are divided into multiple first horizontal bars and second horizontal bars. The first horizontal bars and the second horizontal bars have the same width and are arranged at intervals; any first horizontal bar is higher than any second horizontal bar, and the corresponding height distance is h; the midline positions of all the horizontal bars include multiple circular regions with equal intervals and sizes.

8. A coordinate system plane calibration method for 2D-PIV according to claim 7, characterized in that, The calibration plate is set as follows: All the circular regions distributed on the first horizontal bars are in the same plane, denoted as the first plane, and are arranged in a matrix. The rectangular area formed by any four adjacent circular regions on the first plane is equal; all the circular regions distributed on the second horizontal bars are in the same plane, denoted as the second plane, and are arranged in a matrix. The rectangular area formed by any four adjacent circular regions on the second plane is equal.

9. A coordinate system plane calibration method for 2D-PIV according to claim 7, characterized in that The calibration plate is set as follows: The rectangular area formed by any four adjacent circular regions on the calibration plate is equal.

10. An application of the method according to any one of claims 1-9 to a coordinate system plane calibration system for 2D-PIV, characterized in that, The system includes the following: A calibration plate for reflecting the received light; A laser device for emitting laser light to the calibration plate to generate a bright area. The angle formed by the laser emission direction of the laser device and the calibration plate is θ; A camera is used to collect in real time an image of a bright area generated by emitting laser light onto a calibration board, and the angle formed by the shooting direction of the camera and the laser emission direction of the laser device is 90°.

Images