Object three-dimensional reconstruction method based on liquid cross section

Abstract

The embodiment of the invention provides an object three-dimensional reconstruction method based on a liquid cross section, and the method comprises the following steps: immersing a to-be-measured object in liquid; moving the to-be-detected object towards the liquid level according to a certain direction and gradually exposing out of the liquid level until the to-be-detected object is completely separated from the liquid level; extracting section contours of the to-be-measured object and the liquid level at different exposure heights; and combining the section contours to realize three-dimensional reconstruction of the to-be-measured object. According to the embodiment of the invention, the liquid is used as a contact medium, flexible contact is realized through the liquid, camera internal and external parameter calibration, laser range finder calibration and motion platform calibration are carried out firstly, and then the liquid level is monitored in real time through the calibrated industrial camera and laser range finder. According to the method, the cross section contours of the to-be-measured object and the liquid level at the corresponding height of the motion platform are synchronously extracted, three-dimensional reconstruction of the object is realized in combination with a camera pinhole imaging model, and the purposes of reducing cost and increasing efficiency are achieved while the to-be-measured object is prevented from being scratched.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional reconstruction technology, and in particular to a method for three-dimensional reconstruction of objects based on liquid cross-sections. Background Technology

[0002] 3D reconstruction refers to the creation of models of 3D objects that are suitable for computer representation and processing. It is a key technology for creating virtual reality that expresses the objective world in computers and is a common scientific problem in fields such as computer-aided geometric design, computer graphics, medical image processing, scientific computing and virtual reality.

[0003] Based on different measurement methods, 3D reconstruction can be divided into contact 3D reconstruction and non-contact 3D reconstruction. Examples of contact 3D reconstruction methods include coordinate measuring machines (CMMs) and profilometers, while non-contact methods include laser scanners and multi-view vision devices. Contact 3D reconstruction methods generally offer higher accuracy than non-contact methods, but due to limitations in their measurement principles, they suffer from the following problems: contact 3D reconstruction methods require special fixtures, leading to higher measurement costs and lower efficiency; furthermore, improper operation during measurement can easily scratch the surface of important parts of the object. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the present invention provides a method for three-dimensional reconstruction of objects based on liquid cross sections, so as to solve the technical problems of high measurement cost, low measurement efficiency, and easy scratching of the surface of important parts of the object by improper operation during measurement in the prior art contact three-dimensional reconstruction method.

[0005] This invention provides a method for three-dimensional reconstruction of an object based on a liquid cross-section, comprising the following steps:

[0006] The object to be tested is immersed in the liquid;

[0007] Move the object to be tested toward the liquid surface in a certain direction and gradually expose it until it is completely removed from the liquid surface;

[0008] Extract the cross-sectional profiles of the object under test and the liquid surface at different exposure heights;

[0009] The three-dimensional reconstruction of the object under test is achieved by combining the contours of each cross section.

[0010] In one embodiment, the method is implemented based on a three-dimensional reconstruction system, which includes:

[0011] A container containing a liquid, wherein the liquid level is located at a certain height inside the container;

[0012] A motion platform is provided at the bottom of a container, and a mounting part for fixing the object to be measured is provided at its top. The motion platform can move in a certain direction away from or towards the liquid surface.

[0013] A uniform light source is positioned on top of the container above the liquid surface to illuminate the container space above the liquid surface.

[0014] Several industrial cameras are used to capture images of the liquid surface.

[0015] Several laser rangefinders are used to determine the position of the liquid surface.

[0016] In one embodiment, the method for three-dimensional reconstruction of an object based on a liquid cross-section includes the following steps:

[0017] Step S1: Calibrate the intrinsic and extrinsic parameters of each industrial camera, and calculate the intrinsic parameter matrix and extrinsic parameter matrix of each industrial camera in the world coordinate system.

[0018] Step S2: Calibrate the pose of each laser rangefinder and calculate the pose of each laser rangefinder in the world coordinate system.

[0019] Step S3: Calibrate the motion direction of the motion platform and calculate the motion direction of the motion platform in the world coordinate system;

[0020] Step S4: Collect image information of the object under test and the liquid surface at different exposure heights, and extract the cross-sectional contours of the object under test and the liquid surface at different exposure heights based on image processing algorithms;

[0021] Step S5: Based on the pinhole imaging model of an industrial camera, realize the three-dimensional reconstruction of the object under test.

[0022] In one embodiment, step S1 includes,

[0023] Step S11: Place the chessboard in different poses in the world coordinate system and acquire the corresponding images of each industrial camera in different poses of the chessboard.

[0024] Step S12: Using Zhang's calibration method combined with the multi-industrial camera stereo calibration method, calculate the intrinsic parameter matrix of each industrial camera and the extrinsic parameter matrix in the world coordinate system.

[0025] In one embodiment, step S2 includes,

[0026] Step S21: Calculate the specific pose of the checkerboard in the world coordinate system using the intrinsic and extrinsic parameters of each industrial camera.

[0027] Step S22: Read the parameters of each laser rangefinder, and calculate the pose of each laser rangefinder in the world coordinate system by combining the pose of the corresponding checkerboard grid in the world coordinate system.

[0028] In one embodiment, step S3 includes,

[0029] Step S31: Place the chessboard squares on the motion platform;

[0030] Step S32: Control the motion platform to move and acquire images captured by each industrial camera;

[0031] Step S33: Calculate the specific pose of the chessboard grid in the world coordinate system during the movement using the intrinsic and extrinsic parameters of each industrial camera.

[0032] Step S33: By calculating the specific pose of the chessboard grid in the world coordinate system during the movement, the motion direction of the motion platform in the world coordinate system is determined.

[0033] In one embodiment, step S4 includes,

[0034] Step S41: Illuminate the liquid surface using a uniform light source;

[0035] Step S42: Fix the object to be tested on the motion platform and immerse it in the liquid;

[0036] Step S43: The object to be tested is gradually lifted out of the liquid surface by the motion platform until it is completely removed from the liquid surface, and during this process, an image of the liquid surface is acquired by an industrial camera.

[0037] Step S44: Filter the images captured by the industrial camera using a mean filtering algorithm;

[0038] Step S45: The images captured by the industrial camera are processed by a histogram equalization algorithm to equalize them.

[0039] Step S46: Process the images captured by the industrial camera using the OTSU algorithm combined with a binarization algorithm;

[0040] Step S47: Delete all regions in the binarized image except for the largest connected component;

[0041] Step S48: Extract the liquid cross-section from the image captured by the industrial camera using an edge detection algorithm.

[0042] In one embodiment, step S5 includes,

[0043] Step S51: Calculate the pose of the liquid surface in the world coordinate system using the parameters of each laser rangefinder;

[0044] Step S52: Based on the pinhole imaging model of an industrial camera, project the edge points of the liquid cross section onto the world coordinate system;

[0045] Step S53: Calculate the coordinates of the intersection point of the liquid section edge and the liquid surface in the world coordinate system;

[0046] Step S54: Control the motion platform to move the object under test, and calculate the coordinates of the intersection point between the object under test and the liquid surface in the world coordinate system at different heights;

[0047] Step S55: Combine the movement of the motion platform with the coordinates of the intersection of the object under test and the liquid surface at the corresponding height in the world coordinate system to realize the three-dimensional reconstruction of the object under test.

[0048] Compared with the prior art, the beneficial effects of the object 3D reconstruction method based on liquid cross section provided by the embodiments of the present invention are as follows: The embodiments of the present invention use liquid as a contact medium to achieve flexible contact. First, the camera's internal and external parameters, laser rangefinder, and motion platform are calibrated. Then, the liquid surface is monitored in real time through the calibrated industrial camera and laser rangefinder, and the cross-sectional contour of the object under test and the liquid surface at the corresponding motion platform height is extracted simultaneously. Combined with the camera's pinhole imaging model, the 3D reconstruction of the object is realized. While avoiding scratches on the object under test, the goal of cost reduction and efficiency improvement is achieved. Attached Figure Description

[0049] Figure 1 A flowchart illustrating a method for three-dimensional reconstruction of an object based on a liquid cross section, provided in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the structure of a three-dimensional reconstruction system involved in a liquid-based three-dimensional object reconstruction method provided in an embodiment of the present invention.

[0051] Figure label:

[0052] 1. Uniform light source; 2. Industrial camera; 3. Metal base; 4. Motion platform; 5. Object to be measured;

[0053] 6. Liquid surface; 7. Laser rangefinder. Detailed Implementation

[0054] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0056] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0057] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application, which have the features described in the claims and are therefore all within the scope of protection defined herein.

[0058] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.

[0059] Specific embodiments of this application are described below with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to ascertain the true intent based on the user's historical operations, and to avoid unnecessary or redundant details that would obscure this application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in various ways with substantially any suitable detailed structure.

[0060] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.

[0061] The principles and features of the present invention are described below with reference to the accompanying drawings. The embodiments described are for illustrative purposes only and are not intended to limit the scope of the invention. The following description, in conjunction with... Figure 1-2 The preferred embodiments of the present invention will be described in further detail below:

[0062] like Figure 1 As shown, this embodiment of the invention provides a method for three-dimensional reconstruction of an object based on a liquid cross-section, including the following steps:

[0063] Immerse the object to be tested, 5, in the liquid;

[0064] Move the object to be tested 5 toward the liquid surface 6 in a certain direction and gradually expose it until it is completely removed from the liquid surface 6.

[0065] Extract the cross-sectional profiles of the object under test 5 and the liquid surface 6 at different exposure heights;

[0066] The three-dimensional reconstruction of the object under test 5 is achieved by combining the contours of each cross section.

[0067] like Figure 2 As shown, in one embodiment, the method is implemented based on a three-dimensional reconstruction system, which includes:

[0068] A container is provided, the container is filled with liquid, and the liquid level 6 is located at a certain height inside the container. In order to avoid the impact of light reflection and light transmission on the liquid level 6 on the collection effect, the liquid should preferably be a dark liquid with low transparency, such as black liquid.

[0069] A motion platform 4 is fixedly installed at the bottom of the container by a metal base 33. The top of the platform is provided with a mounting part for fixing the object to be measured 5. The motion platform 4 can move in a certain direction away from or towards the liquid surface 6. To reduce the difficulty of data processing, the motion of the motion platform 4 is set to reciprocate along the vertical Z direction.

[0070] A uniform light source 1 is disposed on the top of the container above the liquid surface 6 to illuminate the container space above the liquid surface 6.

[0071] Several industrial cameras 2 are used to capture image information at the liquid surface 6. The industrial cameras 2 are preferably evenly distributed around the object to be measured 5 so that the exposed position of the object to be measured 5 can be captured completely without blind spots.

[0072] Several laser rangefinders 7 are used to determine the position of the liquid surface 6. At least three laser rangefinders 7 are provided so that they can uniquely and accurately determine the position of the liquid surface 6.

[0073] Based on the above-mentioned three-dimensional reconstruction system, this embodiment of the invention also provides a method for three-dimensional reconstruction of an object based on a liquid cross-section, comprising the following steps:

[0074] Step S1: Calibrate the intrinsic and extrinsic parameters of each industrial camera 2, and calculate the intrinsic parameter matrix and extrinsic parameter matrix of each industrial camera 2 in the world coordinate system. Specifically, this includes...

[0075] Step S11: Place the chessboard in different poses in the world coordinate system and acquire the corresponding images of each industrial camera 2 in different poses of the chessboard.

[0076] Step S12: Using Zhang's calibration method combined with the stereo calibration method of multiple industrial cameras 2, calculate the intrinsic parameter matrix of each industrial camera 2 and the extrinsic parameter matrix in the world coordinate system.

[0077] Place the circular calibration plate within the field of view of the industrial camera and take pictures of the circular calibration plate through each camera;

[0078] The circular calibration plate is reconstructed using the principle of multi-view vision. By comparing the reconstruction results with the standard values, the intrinsic parameter matrix of each industrial camera 2 is optimized and calculated in combination with the optimization principle.

[0079] Step S2: Pose calibration of each laser rangefinder 7, calculating the pose of each laser rangefinder 7 in the world coordinate system, specifically including...

[0080] Step S21: Calculate the specific pose of the chessboard in the world coordinate system using the intrinsic and extrinsic parameters of each industrial camera 2.

[0081] Step S22: Read the parameters of each laser rangefinder 7, combine them with the pose of the corresponding checkerboard grid in the world coordinate system, and use the optimization algorithm to calculate the pose of each laser rangefinder 7 in the world coordinate system.

[0082] Step S3, calibration of the motion direction of motion platform 4, calculating the motion direction of motion platform 4 in the world coordinate system, specifically including,

[0083] Step S31: Place the chessboard squares on the motion platform 4;

[0084] Step S32: Control the motion platform 4 to move and acquire images captured by each industrial camera 2;

[0085] Step S33: Calculate the specific pose of the chessboard grid in the world coordinate system during the movement using the intrinsic and extrinsic parameters of each industrial camera 2.

[0086] Step S33: By calculating the specific pose of the chessboard grid in the world coordinate system during the movement, the motion direction of the motion platform 4 in the world coordinate system is determined.

[0087] Step S4 involves acquiring image information of the object 5 and the liquid surface 6 at different exposure heights, and extracting the cross-sectional contours of the object 5 and the liquid surface 6 at different exposure heights based on image processing algorithms. Specifically, this includes...

[0088] Step S41: Illuminate the liquid surface 6 using a uniform light source 1;

[0089] Step S42: Fix the object to be tested 5 on the motion platform 4 and immerse it in the liquid;

[0090] Step S43: The motion platform 4 drives the object under test 5 to gradually emerge from the liquid surface 6 until it is completely removed from the liquid surface 6, and during this process, the industrial camera 2 acquires an image of the liquid surface 6.

[0091] Step S44: Filter the image captured by industrial camera 2 using a mean filtering algorithm;

[0092] Step S45: The images captured by the industrial camera 2 are processed by the histogram equalization algorithm to equalize them.

[0093] Step S46: Process the image captured by industrial camera 2 using the OTSU algorithm combined with a binarization algorithm;

[0094] Step S47: Delete all regions in the binarized image except for the largest connected component;

[0095] Step S48: Extract the liquid cross-section from the image captured by industrial camera 2 using an edge detection algorithm;

[0096] Step S5, based on the pinhole imaging model of industrial camera 2, realize the three-dimensional reconstruction of the object under test 5, specifically including,

[0097] Step S51: Calculate the pose of the liquid surface 6 in the world coordinate system using the parameters of each laser rangefinder 7.

[0098] Step S52: Based on the pinhole imaging model of industrial camera 2, project the edge points of the liquid cross section onto the world coordinate system;

[0099] Step S53: Calculate the coordinates of the intersection point of the liquid section edge point and the liquid surface 6 in the world coordinate system;

[0100] Step S54: Control the motion platform 4 to move the object under test 5, and calculate the coordinates of the intersection point of the object under test 5 and the liquid surface 6 at different heights in the world coordinate system.

[0101] Step S55: Combine the movement of the motion platform 4 with the coordinates of the intersection of the object under test 5 and the liquid surface 6 at the corresponding height in the world coordinate system to realize the three-dimensional reconstruction of the object under test 5.

[0102] Place the standard ball in the system described above and reconstruct the standard ball using the method described above;

[0103] By comparing the reconstruction results with the standard values, and combining the optimization principle, the laser sensor pose and displacement stage pose calibration results are uniformly optimized and calculated.

[0104] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for three-dimensional reconstruction of an object based on liquid sections, characterized in that, The method comprises the following steps: immersing the object to be measured in a liquid; moving the object to be measured in a certain direction towards the liquid surface and gradually exposing the liquid surface until completely leaving the liquid surface; extracting the cross-sectional profile of the object to be measured at different exposure heights from the liquid surface; combining the cross-sectional profiles to realize three-dimensional reconstruction of the object to be measured.

2. The object three-dimensional reconstruction method based on liquid section according to claim 1, characterized in that: Based on the three-dimensional reconstruction system, the three-dimensional reconstruction system comprises, a container, the container contains a liquid, and the liquid surface is located at a certain height position in the container; a moving platform, the moving platform is arranged at the bottom of the container, the top of the moving platform is provided with a mounting part for fixing the object to be measured, and the moving platform can move in a certain direction away from or close to the liquid surface; a uniform light source, the uniform light source is arranged at the top of the container above the liquid surface, and is used for illuminating the space of the container above the liquid surface; a plurality of industrial cameras for shooting image information at the liquid surface; a plurality of laser range finders for determining the position of the liquid surface.

3. The object three-dimensional reconstruction method based on liquid section according to claim 2, characterized in that, The method comprises the following steps: Step S1, calibrating the internal and external parameters of each industrial camera, calculating the internal parameter matrix of each industrial camera and the external parameter matrix in the world coordinate system; Step S2, calibrating the pose of each laser range finder, calculating the pose of each laser range finder in the world coordinate system; Step S3, calibrating the moving direction of the moving platform, calculating the moving direction of the moving platform in the world coordinate system; Step S4, collecting image information of the object to be measured at different exposure heights from the liquid surface, and extracting the cross-sectional profile of the object to be measured at different exposure heights from the liquid surface based on image processing algorithm; Step S5, based on the pinhole imaging model of the industrial camera, realizing three-dimensional reconstruction of the object to be measured.

4. The object three-dimensional reconstruction method based on liquid section according to claim 3, characterized in that: The step S1 comprises, Step S11, placing the checkerboard in different poses in the world coordinate system, and obtaining the corresponding pictures of each industrial camera in different poses of the checkerboard; Step S12, calculating the internal parameter matrix of each industrial camera and the external parameter matrix in the world coordinate system by using Zhang's calibration method combined with multi-industrial camera stereo calibration method.

5. The method of claim 3, wherein the method further comprises: The step S2 comprises, Step S21, calculating the specific pose of the checkerboard in the world coordinate system through the internal and external parameters of each industrial camera; Step S22, reading the parameters of each laser range finder, and combining the pose of the corresponding checkerboard in the world coordinate system to solve the pose of each laser range finder in the world coordinate system.

6. The object three-dimensional reconstruction method based on liquid section according to claim 3, characterized in that: The step S3 comprises, Step S31, placing the checkerboard on the moving platform; Step S32, controlling the moving platform to move and obtaining the pictures shot by each industrial camera; Step S33, calculating the specific pose of the checkerboard in the world coordinate system during the movement through the internal and external parameters of each industrial camera; Step S33, solving the moving direction of the moving platform in the world coordinate system through the specific pose of the checkerboard in the world coordinate system during the movement.

7. The object three-dimensional reconstruction method based on liquid section according to claim 3, characterized in that: The step S4 comprises, Step S41, illuminating the liquid surface with the uniform light source; Step S42, fixing the object to be measured on the moving platform and immersing it in the liquid; Step S43, gradually exposing the liquid surface by the moving platform with the object to be measured until completely leaving the liquid surface, and obtaining the pictures at the liquid surface by the industrial camera during the process; Step S44, filtering the picture taken by the industrial camera through a mean filter algorithm; Step S45, equalizing the picture taken by the industrial camera through a histogram equalization algorithm; Step S46, processing the picture taken by the industrial camera through an OTSU algorithm combined with a binary algorithm; Step S47, deleting all regions in the picture after binary processing except the largest connected domain; Step S48, extracting the liquid cross section in the picture taken by the industrial camera through an edge detection algorithm.

8. The object three-dimensional reconstruction method based on liquid section according to claim 3, characterized in that: The step S5 comprises, Step S51, calculating the pose of the liquid surface in the world coordinate system through the parameters of each laser range finder; Step S52, projecting the edge points of the liquid cross section into the world coordinate system based on the pinhole imaging model of the industrial camera; Step S53, calculating the coordinates of the intersection of the edge points of the liquid cross section and the liquid surface in the world coordinate system; Step S54, controlling the motion platform to move the object to be measured, and calculating the coordinates of the intersection of the object to be measured and the liquid surface in the world coordinate system at different heights; Step S55, combining the movement of the motion platform with the coordinates of the intersection of the object to be measured and the liquid surface in the world coordinate system at the corresponding height to realize the three-dimensional reconstruction of the object to be measured.

Images