Three-dimensional Measurement Method Research Articles

Calibration Method for Line-Structured Light Three-Dimensional Measurements Based on a Single Circular Target

Single circular targets are widely used as calibration objects during line-structured light three-dimensional (3D) measurements because they are versatile and easy to manufacture. This paper proposes a new calibration method for line-structured light 3D measurements based on a single circular target. First, the target is placed in several positions and illuminated by a light beam emitted from a laser projector. A camera captures the resulting images and extracts an elliptic fitting profile of the target and the laser stripe. Second, an elliptical cone equation defined by the elliptic fitting profile and optical center of the camera is established based on the projective geometry. By combining the obtained elliptical cone and the known diameter of the circular target, two possible positions and orientations of the circular target are determined and two groups of 3D intersection points between the light plane and the circular target are identified. Finally, the correct group of 3D intersection points is filtered and the light plane is progressively fitted. The accuracy and effectiveness of the proposed method are verified both theoretically and experimentally. The obtained results indicate that a calibration accuracy of 0.05 mm can be achieved for an 80 mm × 80 mm planar target.

Method of Three-dimensional Deformation Measurement for Monocular Microscopic Imaging System

Method of Three-dimensional Deformation Measurement for Monocular Microscopic Imaging System

A Stationary Clutter Suppression Method for 3-D Micromotion Measurements Based on Wideband Radar Amplitude and Phase Information

The micromotion features of a target contain unique structural information and motion information about the target, which can be used as an important basis for target classification and recognition. To achieve high-accuracy three-dimensional micromotion measurements in the clutter environment, a stationary clutter suppression method for three-dimensional micromotion measurements based on wideband radar amplitude and phase information is proposed in this paper. This method is capable of accurately measuring the trajectory of small amplitude micromotion with the high-accuracy phase-derived angle measurement (PDAM) and phase-derived range measurement (PDRM). However, the measurement accuracy of three-dimensional micromotion deteriorates sharply when clutter exists. Thus, the main challenge that we overcome is achieving high-accuracy clutter estimation based on wideband radar measurements. The clutter suppression method is proposed by utilizing wideband radar amplitude and phase of multiple range cells jointly. Finally, simulation and experiment are presented to validate the feasibility and effectiveness of the proposed method under stationary clutter conditions.

Dynamic Three-Dimensional Shape Measurement Method Based on Misaligned Gray Code

Dynamic Three-Dimensional Shape Measurement Method Based on Misaligned Gray Code

Phase Unwrapped Method of Modified Fringe Order

Phase measurement profilometry is an optical three-dimensional measurement method, in which phase is the key factor to accurately obtain the three-dimensional coordinates of the measured object, but there will be phase jump error in phase unwrapped process. In order to eliminate the phase jump error existing in the phase unwrapped process based on the principle of multi-frequency heterodyne, a phase unwrapped method with modified fringe orders is proposed. Modifying the integer part of the fringe orders according to the relationship between the integer part of the fringe orders of adjacent pixels can effectively eliminate the jump of the fringe orders caused by the small error, and avoid the transmission and amplification of the phase jump error in the process of fringe heterodyne. Using the multi-frequency characteristic, the absolute phase of the fringe with the middle period is solved by combining the phase information of the fringe with different periods, so as to improve the accuracy of the phase details of the solution. Both simulation and experimental results show that the proposed method has obvious correction effect on the phase jump error, and the unwrapped phase is smoother. Compared with existing methods, the phase error of the proposed method is reduced by an average of 23%.

Three-dimensional measurement method of highly reflective surface based on per-pixel modulation

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Improved Three-Dimensional Measurement Method for Structured Light Phase

Improved Three-Dimensional Measurement Method for Structured Light Phase

Three-Dimensional Measurement Method of Defects Based on Binocular Grating Reconstruction and Texture Mapping

Three-Dimensional Measurement Method of Defects Based on Binocular Grating Reconstruction and Texture Mapping

Three-dimensional Measurement Method of Glue Surface During the Mounting Process of Micro-camera Module

Three-dimensional Measurement Method of Glue Surface During the Mounting Process of Micro-camera Module

Whole Three-Dimensional Dosimetry of Carbon Ion Beams with an MRI-Based Nanocomposite Fricke Gel Dosimeter Using Rapid T1 Mapping Method.

MRI-based gel dosimeters are attractive systems for the evaluation of complex dose distributions in radiotherapy. In particular, the nanocomposite Fricke gel dosimeter is one among a few dosimeters capable of accurately evaluating the dose distribution of heavy ion beams. In contrast, reduction of the scanning time is a challenging issue for the acquisition of three-dimensional volume data. In this study, we investigated a three-dimensional dose distribution measurement method for heavy ion beams using variable flip angle (VFA), which is expected to significantly reduce the MRI scanning time. Our findings clarified that the whole three-dimensional dose distribution could be evaluated within the conventional imaging time (20 min) and quality of one cross-section.

A free field recovery technique based on the boundary element method and three-dimensional scanning measurements.

The boundary element method- (BEM-) based free field recovery technique (FFRT) has been proposed to recover the free field radiated by an arbitrarily shaped source from the mixed field that would be measured in a noisy environment. However, that technique requires that the boundary integral equation should be established on an enclosed hologram surface surrounding the source, which means that the hologram surface should be discretized into elements and the measurement points should be located on the nodes of the elements. For large-scale or mid-high frequency problems, it makes the total number of measurement points huge since it should obey the criterion of more than six elements per wavelength, which put forward very high requirements for holographic data measurement. To overcome this problem, a more flexible BEM-based FFRT without the restriction on the locations of measurement points is proposed in this study. In virtue of this, a three-dimensional scanning measurement method can be applied to acquire holographic data with high efficiency. The effectiveness of the proposed method is validated by two numerical simulations and an experiment.

Software package for testing three-dimensional shape measurement methods using structured lighting

This work aims at creating a universal software package for the development and testing of triangulation methods using structured lighting for measuring the three-dimensional geometry of objects in difficult ambient lighting conditions. As a result, a software package meeting the stated requirements is created. Lighting is based on the Fong model. A method for preloading objects is implemented to optimize the operation of the software package. An accelerated method for creating shadow maps is proposed and implemented. The developed software package is shown to successfully perform all required functions.

Three-dimensional micro-displacement measurement method based on capacitance-grating sensor

In order to solve the problems that it‘s difficult in installing a sensor in a narrow space and identifying micro-displacement direction in micro-displacement measurement. A three-dimensional micro-displacement measurement method based on capacitance-grating sensor was proposed by highlighting the idea of combining several groups of capacitance grids and the theory of displacement coordinate decomposition. The sensor structure was optimized and a three-dimensional micro-displacement test system was also established. By taking into consideration the positional relationship of the sensors in measurement model, a micro-displacement measurement model of sphere eccentricity was established to deduce the relationship between the displacement in the x,y and z directions and capacitance change. The relationship between the displacement direction and the capacitance change trend was also analyzed, based on which, a three-dimensional spatial micro-displacement decoupling mathematical model was established to measure displacement and judge the specific direction. BP neural network was also used to realize the decoupling of three-dimensional spatial micro-displacement and verification of decoupling accuracy. Under the ideal simulation conditions, the decoupling errors in x,y and z directions are less than 4 μm. The experimental results show that decoupling errors are all less than 8 μm. According to the results, the three-dimensional micro-displacement measurement method based on capacitance-grating sensor could measure the three-dimensional micro-displacement and identify the direction. The accuracy could reach 1.6% over the full range of sensor.

High-precision 3D shape measurement of rigid moving objects based on the Hilbert transform.

Phase-shifting profilometry (PSP) is a three-dimensional (3D) measurement method of point-to-point calculation. The consistency of object position is the prerequisite to ensure the successful application of PSP in moving objects. The position information of an object can be well characterized by the modulation patterns, and hence a high-quality modulation pattern is the guarantee of pixel-matching accuracy. In this paper, a generic modulation pattern enhancement method for rigid moving objects based on the Hilbert transform is proposed. First, the Hilbert transform is employed to suppress the zero-frequency components of the fringe pattern, and a hybrid digital filter window is applied to filter out the positive fundamental frequency components for a higher signal-to-noise ratio. Then the grid-based motion statistics for fast, ultra-robust feature correspondence algorithm is used to match the high-quality modulation patterns between two adjacent frames, and the object positions in the three deformed patterns are made consistent by image clipping. Finally, the three-step PSP is used to reconstruct the 3D shape of the measured object. Experimental results demonstrate that the proposed method can substantially improve the quality of the modulation pattern, achieve high-precision pixel matching, and ultimately reduce the motion-introduced phase error.

Three-dimensional measurement method for pavement texture depth using an optimized digital speckle correlation method

Motivated by the low efficiency and poor accuracy of the existing techniques for measuring the depth of a pavement structure, we examine the characteristics of laser speckle and speckle measurement methods in relation to the depth of a pavement structure and propose a set of methods for the 3D measurement of such structures based on laser speckle and digital image processing. First, we analyze the relevant characteristics of laser speckle measurement, and then based on the relevant region and temporal sequence correlation, a faster digital speckle correlation method is used to establish a mathematical relationship between the 3D image and the structural depth. The erosion and dilation technique and mean optimization algorithm are proposed to eliminate the noise and burr of primeval 3D reconstruction. After this, a 3D point cloud of information on the depth of the pavement structure is obtained. Finally, through fitting, a good linear relationship was found between the texture depth obtained by the sand paving method and the system. From measurements using a laboratory calibration platform, it was found that the accuracy of measurement of our method can reach the subpixel level, and the running speed is high, meaning that it can be used for highly efficient and accurate detection of the depth of a road structure.

3D non-axisymmetric temperature field measurement using rotating tomographic mechanism schlieren method

The tomography schlieren method is useful for calculating the non-axisymmetric temperature field, which is relevant to many industrial applications. However, the traditional tomography schlieren method requires bulky imaging devices, which limits its application. Thus, this paper proposes a non-contact three-dimensional temperature field measurement method based on the rotating tomography schlieren method. Projections from different directions of the temperature field are obtained at different angles using a transmission schlieren system, which is controlled by a designed rotating tomographic mechanism. The calibration schlieren method and the projection reconstruction algorithm are used to calculate the 3D temperature field. Verification experiments of single flame and double flame showed that the relative error of the reconstructed temperature was approximately 3.7% compared with a precision thermocouple.

Rapid 3D measurement of high dynamic range surface based on multi-polarization fringe projection

It is challenging to measure objects with a high dynamic range surface. We propose a three-dimensional measurement method of high dynamic surfaces based on multi-polarization fringe projection. The saturated pixels can be recognized to get the optimal exposure time by projecting a series of designed auxiliary patterns onto the surface of the object. It does not need to project multiple N-step phase-shifting fringe patterns for recognition, and it greatly improves the detection speed and efficiency. A multi-polarization camera captures full-resolution phase-shifting images with four polarization directions simultaneously. An appropriate polarization direction is selected by analyzing the per-pixel of auxiliary images captured by camera, and then optimal phase-shifting fringe images with high quality are obtained. The effectiveness and rapidness of this method are verified by the measurement experiments of different objects, and the method provides a new idea for rapid measurement.

Computer-generated frequency-carrier moiré profilometry

A three-dimensional measurement method based on frequency-carrier computer-generated moiré fringe is proposed. By projecting two sinusoidal gratings with π phase difference each other onto the measured object respectively and capturing the corresponding deformed patterns, the AC component of the deformed pattern can be extracted. When this AC component is respectively multiplied by actively designed computer-generated sinusoidal grating and cosinoidal grating with the same frequency, two new fringes containing frequency-carrier moiré components can be obtained. After low-pass filtering, the frequency-carrier moiré fringes can be extracted to achieve object’s phase retrieval. As long as the DC component of the actively designed sinusoidal grating and cosinoidal grating are all controlled to be zero, the effect of inaccuracy elimination of the deformed pattern’s background light component on measuring accuracy can be reduced evidently. The frequency of the actively designed grating can be determined as 1/4 lines per pixel to ensure the maximum distance between each adjacent spectrum peaks of the new generated fringe so as to get the best measurement effect. The proposed method has good application ability in the limited number of projection frames and other scenes, and can achieve high measurement accuracy by projecting only two fringe patterns. Experimental results verify the feasibility and validity of the proposed method.

Three-dimensional measurement method of color fringe projection based on an improved three-step phase-shifting method.

A three-dimensional (3D) measurement method of color fringe projection based on an improved three-step phase-shifting method is proposed. The color fringe pattern is encoded by two cosine fringe patterns with the same frequency but different shifting phase and a uniform gray flat image into three color channels R, G, and B. Although the measurement speed of the traditional three-step phase-shifting method can meet the requirements of measuring 3D objects, it makes the noise and inaccuracy of the captured images increase, and each image will cause measurement error. Therefore, we improve the three-step phase-shifting method and introduce the Hilbert transform into the three-step phase-shift method. The DC component of the fringe pattern is obtained by using the Hilbert transform principle, and the third fringe pattern in the three-step phase-shift method is replaced by the captured light intensity distribution of the DC component. The phase difference of the other two fringe patterns is fixed as π/2 by the Hilbert transform. The improved three-step phase-shifting method is used to obtain the phase information of the deformed color fringe image, and then the phase-unwrapping algorithm is used to obtain the phase distribution information of the whole field. The results show that the improved method can not only accurately calculate the phase information but also greatly improve the measurement speed and quality.

APPLICATION OF 3D ANALYSIS TECHNOLOGY OF VISION SYSTEM IMAGE IN SPORTS MEDICINE

ABSTRACT Background: Objective: The study of sports biomechanics in sports medicine usually requires a special image analysis system (software) to obtain 3D kinematics data. Taking the swimming project in sports medicine as an example, 3D water images in water have always been relatively complicated and difficult. As light travels in different media, it will refract and reflect. When testing underwater movements, if only a land camera or an underwater camera is used for testing, the error caused by light refraction will be larger, which will affect the accuracy of the test data even more. Methods: Taking breaststroke movement as an example, a three-dimensional measurement method based on the Kwon3D movement analysis system is introduced. This method is different from the simple underwater camera test. It is a three-dimensional test method combining a land camera and an underwater camera. Two underwater cameras and two land cameras were used to simultaneously calibrate the water and underwater space with the same calibration frame in the experiment after analyzing and verifying the accuracy of 3D reconstruction. Results: The comprehensive reconstruction error is small, and the average relative error is less than 1%. Conclusions: The application of three-dimensional image analysis technology of vision systems in sports medicine is reasonable and worth promoting. Level of evidence II; Therapeutic studies - investigation of treatment results.