A composite-structured-light 3D measurement method based on fringe parameter calibration

3D measurement system based on divergent multi-line structured light projection, its accuracy analysis

Background This study aimed to investigate factors, such as differences in femoral shape, that could affect the femoral valgus correction angle (VCA) for the intramedullary alignment rod (IM rod) by using a three-dimensional (3D) measurement system in patients with varus knee osteoarthritis undergoing total knee arthroplasty (TKA). Methods A total of 305 knees in 233 Japanese patients with varus knee osteoarthritis who underwent primary TKA by using Jig Engaged 3D Pre-Operative Planning Software for the TKA operation support system was examined. We retrospectively analysed factors, such as the shape of the proximal, middle, and distal femur in the coronal plane, all of which could affect the VCA for the IM rod, by multiple linear regression analyses. Results The VCA for the IM rod was 5.9° ± 1.6° (range: 1.7° to 10.7°), and the femoral lateral bowing angle (FBA) was 3.5° ± 3.2°. Major factors independently associated with the VCA for the IM rod were the FBA (β: 0.75), femoral offset (β: 0.38), and the medial angle between the mechanical femoral axis and the line that connects the distal margins of the medial and lateral femoral condyles (β: −0.16). The model was created by stepwise multiple linear regression (F = 266.6, p < 0.001, and estimated effect size = 4.4) explained 85% of the variance in the VCA for the IM rod (R2 = 0.85). Conclusions The VCA for the IM rod was most strongly associated with femoral lateral bowing in patients with varus knee osteoarthritis undergoing TKA. Our findings suggest that preoperatively measuring the VCA for the IM rod in patients with femoral lateral bowing by using a 3D measurement system could be useful for accurate coronal alignment of the femoral component in TKA.

A three-dimensional (3D) measurement system with spectroscopic function was demonstrated using a practical supercontinuum light source and an all-fiber interferometer. Spectral information was obtained by Fourier transformation of the observed interference signal. We obtained the absorbances of various plastics. In addition, the system was capable of discerning different surface asperities that were smaller than the spatial resolution of the system by observing the spectral modulation caused by spectral interference that occurred when there was an asperity in the irradiated beam spot. The frequency of the spectral modulation depended on the height of the asperity. In this paper, the spectral modulation was analyzed by numerical calculations, and images based on the spectral modulation differences were obtained experimentally. The longitudinal and transverse resolutions were 3.0 and 125 µm, respectively. Based on the spectral modulation, we demonstrated that our 3D measurement system could obtain images of asperities of diameters 3, 6, 15, and 90 µm, which were smaller than the spatial resolution. A clear 3D image of a metallic cylinder with a small blemish was also obtained using this system.

3D human body parameters measurement is a challenging task due to two main reasons: (i) it is difficult to reconstruct 3D human model due to flexible deformation of non‐rigid body during images capturing process and (ii) there lies a gap between 3D model and body parameters. To address these two issues, a 3D human body parameters measurement system is represented. With the object freely spinning in front of a Kinect, body parameters are calculated. To reduce registration errors caused by body deformation while rotating, a piecewise tracking and mapping algorithm based on KinectFusion framework is proposed. Then model–model iterative closest point and non‐rigid constraints are introduced to optimise alignments and disambiguate different surfaces caused by aliasing in the piecewise strategy. Finally, a novel method is presented to measure the volume and perimeter of human body with the truncated signed distance function values of voxels. Extensive experimental results show that the proposed method achieves comparable accuracy to the state of the arts, and the error of volume and perimeter measurements are 2.0 and 5.8%, respectively.

The basis of the described 3D-measurement system is the method of fringe projection in combination with the principle of uniform scale representation /1 1, /2/, /3/. The measurement is characterized by the exclusive use of phase-measurement values for the coordinates of each point. To obtain the phase-measurement values the object under test is successively illuminated with a grating structure from at least three different directions with a telecentric system. A CCD-camera records the intensity distribution of the fringes intersected by the object. It should be pointed out that the values of all coordinates (x,y,z) have the same accuracies. The object to be measured and the CCD-camera are both mounted on a rotation table, turning both of them with respect to the fringe-projector about an axis. The rotation axis makes a constant angle c with the projection direction. With at least i = 3 different angle values e the linearly independent absolute phase values are obtained, which are necessary for the coordinate calculation (applying gray-code in conjunction with four 90 degs phase-shifts). In our setup we can choose up to I = 1 5 rotation angles, so that awkward areas of the surface, like zones with either specular reflection or shadows, are shifted over the surface and have nearly no influence on the results of measurements. So, we obtain the 3D-coordinates of a single patch of the object. We have expanded the system to include a second rotation axis, where the object can rotate within the measurement volume. The CCD-camera will then get different views of the object. The second rotation axis is tilted against the first axis by an angle S. Depending on the class of objects there are different possible tilt-angles S. Typically we choose ö = 300. By rotating the object around the first axis with a rotation angle -y (j = number of patches) it is possible to measure the object from different viewpoints, whereby for each patch or viewpoint the procedure described above is used. For a convenient handling of the data-set the restriction j 8 is used. The actual rotation angles e and y were measured with angle encoders. The free geometric parameters (grating periode A and projection angle a) and the orientation in space of the second axis are gauged before the measurement procedure as described below. By measuring a number of patches we have the problem of transforming them from a local coordinate system into a global one. The combination of the different patches into one coordinate system without interactive user help was solved by developing a calibration method for the second axis. In combination with an absolute phase measurement all patches were measured in a known space orientation, so that we obtain the 3D-picture by rotation of each patch around the second axis. Correlation methods or special points are not necessary. To obtain the 3Dorientation of the second axis one can use a calibration procedure with a special calibration body whose 3Dcoordinates are measured for different rotation positions whereby the second axis has to cross the plane near the centre.

New EOS Imaging Protocol Allows a Substantial Reduction in Radiation Exposure for Scoliosis Patients

An improved algorithm for phase-to-height mapping in phase-measuring profilometry (PMP) is proposed, in which the phase-to-height mapping relationship is no longer restricted to the condition that the optical axes of the imaging system must be orthogonal to the reference plane in the basic PMP. Only seven coefficients independent of the coordinate system need to be calibrated, and the system calibration can be accomplished using only two different gauge blocks, instead of more than three different standard planes. With the proposed algorithm, both the phase measurement and system calibration can be completed simultaneously, which makes the three-dimensional (3-D) measurement faster and more flexible. Experiments have verified its feasibility and validity.

The first purpose of this study was to compare the reproducibility of two-dimensional (2D) and three-dimensional (3D) measurements for preoperative planning of the femoral side in total knee arthroplasty (TKA). The second purpose was to evaluate the factors affecting the differences between the 2D and 3D measurements. Two-dimensional and 3D measurements for preoperative planning of the femoral side in TKA were evaluated in 75 varus knees with osteoarthritis. The femoral valgus angle, defined as the angle between the mechanical and anatomical axes of the femur, and the clinical rotation angle and surgical rotation angle, defined by the angles between the posterior condylar line and the clinical or surgical transepicondylar axes, respectively, were analysed using 2D (radiographs and axial CT slices) and 3D (3D bone models reconstructed from CT images) measurements. For all variables, 3D measurements were more reliable and reproducible than 2D measurements. The medians and ranges of the clinical rotation angle and surgical rotation angle were 6.6° (-1.7° to 12.1°) and 2.3° (-2.5° to 8.6°) in 2D, and 7.1° (2.7° to 11.4°) and 3.0° (-2.0° to 7.5°) in 3D. Varus/valgus alteration of the CT scanning direction relative to the mechanical axis affected the difference in clinical rotation angles between 2D and 3D measurements. Significantly, smaller values of the clinical rotation angle and surgical rotation angle were obtained by 2D compared to 3D measurements, which could result in internal rotation of the femoral component even if the surgeon performs the bone cutting precisely. Regarding clinical relevance, first, this study confirmed the reliability of 3D measurements. Second, it underscored the risk of internal rotation of the femoral component when using 2D measurement, even with precise bone cutting technique. These results will help surgeons avoid malpositioning of the femoral component if 2D measurements are used for preoperative planning in TKA. Prospective comparative study, Level Ш.

Analysis and compensation of lateral chromatic aberration of structured light 3D measurement system

A method to recognize unpaved road region using a 3D depth measurement system is proposed for mobile robots. For autonomous maneuvering of mobile robots, recognition of obstacles or recognition of road region is the essential task. In this paper, the 3D depth measurement system which is composed of a rotating mirror, a line laser and mono-camera is employed to detect depth, where the laser light is reflected by the mirror and projected to the scene objects whose locations are to be determined. The obtained depth information is converted into an image. Such depth images of the road region represent even and plane while that of off-road region is irregular or textured. Therefore, the problem falls into a texture identification problem. Road region is detected employing a simple spatial differentiation technique to detect the plain textured area. Identification results of the diverse situation of unpaved trail are included in this paper.

With more than three decades of development, three-dimensional optical measurement technology has reached a mature stage in commercial applications, meanwhile new ones have continually arisen. Due to the development of Charge Coupled Device (CCD) array camera and digital projection technology, the applications of Phase Measurement Profilometry (PMP) become more and more broad. Among these, dual-frequency grating method has drawn many attentions because of its simplicity in principle and optical path, low requirement of equipment, high accuracy and level of automation comparing with other methods. The phase calculation is one of the key technologies in PMP. However, phase unwrapping algorithm in PMP is a difficult issue. A lot of new algorithm have been proposed, but neither one can solve all the problems, so how to set up new phase unwrapping algorithm becomes urgent. In this chapter, we systematically investigate the phase unwrapping method in dual-frequency grating method, and experimentally set up the system. To verify our method, we experimentally measure a three dimensional object which possesses complicated stair shapes on its surface. The results show that our dual-frequency grating method could achieve phase unwrapping without doing conventional phase unwrapping calculations, and it could also detect the detailed stair shapes on the surface of this three dimensional object automatically.

Application of grayscale expansion for accuracy improvement in phase-measuring profilometry

Assessing distal radius malunions traditionally relies on measuring volar tilt and radial inclination in 2D radiographs. Reliability of these parameters is limited by projection errors and landmark ambiguity. Using 3D models allows more precise quantification of these parameters. This study validated an algorithm for measuring volar tilt and radial inclination on 3D virtual models of malunited and healthy radii. The algorithm establishes a 3D coordinate system and anatomical landmarks replicating conventional 2D definitions to maintain clinical compatibility. Automatic 3D measurements on models from 16 participants were compared with manual measurements on 2D radiographs (by three surgeons in consensus) and on 3D models (by two independent raters). Agreement was assessed using Bland-Altman analysis, and landmark discrepancies were quantified. Mean differences between automatic 3D and manual 2D measurements were small: for volar tilt, 2.0° in malunited and 3.5° in healthy radii; for radial inclination, 1.5° and 2.3°, respectively. Strong agreement was also found between automatic and manual 3D measurements. Landmark deviations ranged from 0.5 to 2.8mm, with an average longitudinal axis difference of 2.5°. This open-source algorithm provides a reproducible 3D assessment of distal radius alignment. By closely matching 2D standards, the algorithm has a high potential for clinical integration.

With the appearance of low-cost and high-resolution consumer-grade digital cameras, a practical three-dimensional (3D) measurement system using a consumer-grade digital camera is greatly anticipated in various fields. In these circumstances, the authors have been concentrating on developing a practical 3D measurement system that includes photogrammetric software called the Image Based Integrated Measurement (IBIM) system. The IBIM system device consists of full/half-mirrors, a consumer-grade digital camera, and a laser distance meter. The most remarkable advantage of the system is its ability to calculate exterior orientation parameters, interior orientation parameters, and pseudo ground control points (GCPs) without using scale bars or the GCPs in the object field. The system has the ability to calibrate multiple cameras of different resolutions using a camera-variant parameter set. However, there remains one issue that needs to be resolved before this system can be effectively used, namely, improvement of the system which does not depend on the IBIM system device. With this motive, a practical photogrammetry method using a consumer-grade digital cameras and a hand-held laser distance meter is proposed. To test our proposed method, the bundle of distances from the center camera position to the feature points in the object field were measured individually at archaeological sites in Greece. In order to evaluate the possibility and practicability of the proposed photogrammetry method, this paper describes and evaluates the camera calibration techniques using images from multiple cameras of different resolutions and a bundle of distances.

A new phase unwrapping algorithm based on Three Wavelength Phase Shift Profilometry method