3D Surface Shape Research Articles

Theoretical considerations on aperiodic sinusoidal fringes in comparison to phase-shifted sinusoidal fringes for high-speed three-dimensional shape measurement.

The demand for optically reconstructing the three-dimensional (3D) surface shape of moving objects or deformation processes makes the development of high-speed projectors necessary. Our 3D sensor containing an array projector can achieve frame rates of several tens of kilohertz and is based on the projection of aperiodic sinusoidal fringes. This approach is compared with phase-shifting fringe projection as probably the most widely used technique. Theoretical considerations as well as extensive simulations are conducted to derive criteria for the design of optimal sequences of aperiodic sinusoidal fringes and to compare the number of patterns of both approaches necessary for comparable accuracies.

Determination of three-dimensional shape of failure in soil slopes

This paper presents the application of particle swarm optimization (PSO) in three-dimensional (3D) slope stability analysis to determine the shape and direction of failure as the critical slip surface. A detailed description of adopted PSO is presented and a rotating ellipsoidal shape is introduced as the possible failure surface in the analysis. Based on the limit equilibrium method, an equation of factor of safety (FoS) was developed with the ability to calculate the direction of sliding (DoS) in its internal process. A computer code was developed in Matlab to determine the 3D shape of the failure surface and calculate its FoS and DoS. Then, two example problems were used to verify the applicability of the presented code, the first by conducting a comparison between the results of the code and PLAXIS-3D finite element software and the second by re-analyzing an example from the literature to find the 3D failure surface. In addition, a hypothetical 3D asymmetric slope was introduced and analyzed to demonstrate the ability of the presented method to determine the shape and DOS of failure in 3D slope stability problems. Finally, a small-scale physical model of a 3D slope under vertical load was constructed and tested in the laboratory and the results were re-analyzed and compared with the code results. The results demonstrate the efficiency and effectiveness of the presented code in determining the 3D shape of the failure surface in soil slopes.

Estimation of 3D surface shape from line drawings: a Bayesian model

Estimation of 3D surface shape from line drawings: a Bayesian model

Consistent quadrangulation for shape collections via feature line co-extraction

This paper presents a method that takes a collection of 3D surface shapes, and produces a consistent and individually feature preserving quadrangulation of each shape. By exploring the correspondence among shapes within a collection, we coherently extract a set of representative feature lines as the key characteristics for the given shapes. Then we compute a smooth cross-field interpolating sparsely distributed directional constraints induced from the feature lines and apply the mixed-integer quadrangulation to generate the quad meshes. We develop a greedy algorithm to extract aligned cut graphs across the shape collection so that the meshes can be aligned in a common parametric domain. Computational results demonstrate that our approach not only produces consistent quad meshes across the entire collection with significant geometry variation but also achieves a trade-off between global structural simplicity for the collection and local geometry fidelity for each shape.

A 3D Scene Registration Method via Covariance Descriptors and an Evolutionary Stable Strategy Game Theory Solver

In this paper we provide an integrated approach for matching patterns in scenes combining 3D and visual information. For local definition of points we propose a descriptor based on the notion of covariance of features for fusion of shape and color information of 3D surfaces, so-called multi-scale covariance descriptor (MCOV). The intrinsic properties of this descriptor are many: it is invariant to spatial rigid transformations, and robust to noise and resolution changes; it can also be used for characteristic point detection; and lies on top of a manifold topology which allows the use of analytical metric properties. This descriptor is complemented with a game theoretic approach for solving the matching correspondences under global geometric constraints. This layer offers a comprehensive understanding of the scene and avoids possible mismatches due to repeated areas or symmetries--which would be impossibly identified by the detector solely at a local level. Our solution is able to accurately match different views of a scene even under spatial transformations, high noise levels and with small overlap between views, outperforming state-of-the-art approaches. Results are validated by comparing MCOV against other state-of-the-art 3D point descriptor methods, and matching complex 3D and color scenes under several challenging conditions.

Profilometric Assessment of Surface Condition of Zinc Coatings Formed by the Continuous Galvanizing Method

The paper presents the results of research on surface condition of zinc coatings. Profilometric studies were performed for zinc coatings formed in industrial continuous hot-dip galvanization process and for the same coatings after two years of use. The results include the geometrical shape of 2D and 3D surfaces, distribution of vertices on the surface and roughness and waviness profiles. The parameters Ra, Rz, Sa and Sz were used to define the surface roughness. The study was conducted using FRT Microprof optical profilometer with data acquisition and analysis by MARK III software package.

Specular Image Structure Modulates the Perception of Three-Dimensional Shape

Retinal images are produced by interactions between a surface's 3D shape, material properties, and surrounding light field. In order to recover the 3D geometry of a surface, the visual system must somehow separate aspects of image structure generated by a surface's shape from structure generated by its material properties or the light field in which it is embedded. Attributing image structure to the wrong physical source would cause the visual system to interpret changes in one physical property (such as reflectance) as changes in another (such as shape). Many previous studies have shown that the visual system does not conflate image structure generated by specular reflectance with 3D shape, but they did not assess the physical conditions where it would be computationally most difficult to disentangle these different sources of image structure. Here, we show that varying the specular roughness and curvature of surfaces embedded in natural light fields can strongly modulate perceived shape. Despite the complexity of these interactions, we show how an image's gradient structure mediates its interpretation as a specular reflection or a change in 3D shape. Our findings provide a coherent explanation of when and why specular reflections impact perceived shape and reveal how the static surface properties, simplified light fields, and experimental methods used in previous studies may explain their inconsistent results.

Three-dimensional geometry of thrust surfaces and the origin of sinuous thrust traces in orogenic belts: Insights from scaled sandbox experiments

Sinuous traces of emerging thrust tips, comprising multiple salients and recesses, are commonly observed in orogenic belts (e.g. Lesser Himalayas of India, Nepal and Bhutan) and in accretionary prisms (e.g. Nankai Trough off the coast of Japan). Lateral (along the strike of the deformation zone) variation in the depths of foreland basins (i.e. variable sediment thickness) or in the strength of the basal detachment, or presence of a curved indenter has been traditionally cited to explain the formation of salients in fold-and-thrust belts, although they are not applicable in all cases. In the present work, we have carried out four series of scaled analog model experiments using dry quartz sand, changing the dip of the basal decollément (β = 0° or 5°) and the basal friction (μb = 0.5 or 0.3) to investigate the 3D shape of thrust surfaces under varying overall boundary conditions, but without any lateral variation of these parameters, within the models. The experimental results show that under all boundary conditions, thrust surfaces are curved both in their dip and strike directions (i.e. spoon-shaped in 3D). Multiple concave-upward and convex-upward segments constitute a thrust surface, which produces a sinuous trace when the tip line intersects the Earth's surface. It is also shown that thrust surface curvatures occur at different scales, and the overall thrust surface roughness (corrugations) has a self-affine fractal geometry.

3D reconstruction of external and internal surfaces of transparent objects from polarization state of highlights.

A vision-based method is proposed to measure the 3D shape of external and internal surfaces (not accessible) of smooth transparent objects. Looking at the reflections of point sources on a specular surface with a polarimetric camera, we combine the measurements of two techniques: shape from distortion and shape from polarization. It permits us to recover the position and orientation of the specular surface for each detected point. The internal surface of transparent objects exhibiting as well a specular component, the same technique is used on the highlights coming from the back surface, taking into account the refraction by using polarimetric ray tracing.

3D soft-tissue tracking using spatial-color joint probability distribution and thin-plate spline model

Visual tracking techniques based on stereo endoscope are developed to measure tissue motion in robot-assisted minimally invasive surgery. However, accurate 3D tracking of tissue surfaces remains challenging due to complicated deformation, poor imaging conditions, specular reflections and other dynamic effects during surgery. This study employs a robust and efficient 3D tracking scheme with two independent recursive processes, namely kernel-based inter-frame motion estimation and model-based intra-frame 3D matching. In the first process, target region is represented in joint spatial-color space for robust estimation. By defining a probabilistic similarity measure, a mean-shift-based iterative algorithm is derived for location of the target region in a new image. In the second process, the thin-plate spline model is used to fit the 3D shape of tissue surfaces around the target region. An iterative algorithm based on an efficient second-order minimization technique is derived to compute optimal model parameters. The two processes can be computed in parallel. Their outputs are combined to recover 3D information about the target region. The performance of the proposed method is validated using phantom heart videos and in vivo videos acquired by the daVinci® surgical robotic platform and a synthesized data set with known ground truth.

Analytical real-time measurement of a three-dimensional weld pool surface

The ability to observe and measure weld pool surfaces in real-time is the core of the foundation for next generation intelligent welding that can partially imitate skilled welders who observe the weld pool to acquire information on the welding process. This study aims at the real-time measurement of the specular three-dimensional (3D) weld pool surface under a strong arc in gas tungsten arc welding (GTAW). An innovative vision system is utilized in this study to project a dot-matrix laser pattern on the specular weld pool surface. Its reflection from the surface is intercepted at a distance from the arc by a diffuse plane. The intercepted laser dots illuminate this plane producing an image showing the reflection pattern. The deformation of this reflection pattern from the projected pattern (e.g. the dot matrix) is used to derive the 3D shape of the reflection surface, i.e., the weld pool surface. Based on careful analysis, the underlying reconstruction problem is formulated mathematically. An analytic solution is proposed to solve this formulated problem resulting in the weld pool surface being reconstructed on average in 3.04 ms during welding experiments. A vision-based monitoring system is thus established to measure the weld pool surface in GTAW in real-time. In order to verify the effectiveness of the proposed reconstruction algorithm, first numerical simulation is conducted. The proposed algorithm is then tested on a spherical convex mirror with a priori knowledge of its geometry. The detailed analysis of the measurement error validates the accuracy of the proposed algorithm. Results from the real-time experiments verify the robustness of the proposed reconstruction algorithm.

Lighting direction and visual field modulate the brightness of 3D objects

Background: When interpreting the shape of 3D surfaces the visual system assumes that illumination is mostly from above and slightly from the left. Visual search is parallel for below-lit targets amidst top-lit distractors, but not vice versa. However, visual search for oddly-illuminated singletons is serial when the 3D pose of cube targets and distractors is randomized. We asked whether the direction of lighting of randomly posed 3D cubes would influence their brightness (and/or perceived intensity of illumination). Method: An array of nine Lambertian cubes was stereoscopically rendered in low ambient illumination against a dark background. Individual cubes varied in their 3D pose, but all possessed identical triplets of visible faces. The cubes were illuminated from one of four directions: top-left (+60o elevation; -90o azimuth); top-right (+60o; +90o); bottom-left (-60o; -90o); and bottom-right (-60o; +90o). Illumination intensity (arbitrary units) ranged from 1-15 (linear steps). "Standard" cubes were illuminated from top-left at intensity 8; comparison cubes were illuminated from all four possible directions, and appeared in either the left or right visual fields. Using the method of adjustment (N=20, 13 male) we determined comparison cube illumination levels required to establish subjective equality with the standard cubes as a function of comparison cube visual field, illumination elevation, and illumination azimuth. Results: Cubes appeared significantly brighter in the left visual field (p=.008), and when illuminated from below (p<.001). There was a trend for right-lit cubes to appear brighter (p=.069). The enhanced brightness of surfaces lit from below was greatest when also lit from the right (p=.001). Conclusions: Surfaces lit from below appear brighter (more illuminated) than identical surfaces lit from above, due perhaps to long-term adaptation to downward lighting. This effect is modulated by azimuth, being strongest for illumination from the right. Brightness is amplified in the left visual field, presumably via attentional enhancement. Meeting abstract presented at VSS 2013

A new reconstruction method based on fringe projection of three-dimensional measuring system

This paper presents a new reconstruction method of three-dimensional measuring system, with the simple calibration process, whole-field calibration and fast reconstruction. First, we project a sinusoidal fringe pattern on the surface of the calibration target within the scope of a calibrated field. At the same time, camera captures fringe images on the planar target. Then, we extract image coordinates and absolute phase values of the feature point of planar target, and obtain camera parameters and world coordinates by using image coordinates. Next, we use fitting polynomials to match the spatial relationships among image coordinates, absolute phases and world coordinates from planar target, solve the parameters from fitting equations. Finally, we solve the absolute phase values of object's surface in phase shifting and gray coding techniques, substitute it into fitting equations and reconstruct 3D shape of object's surface. The experimental results show that this reconstruction method is simple, with high precision. Most of all, the calibration target can be placed arbitrarily within entire calibrated fields in the calibration procedure.

A measurement method for micro 3D shape based on grids-processing and stereovision technology

An integrated measurement method for micro 3D surface shape by a combination of stereovision technology in a scanning electron microscope (SEM) and grids-processing methodology is proposed. The principle of the proposed method is introduced in detail. By capturing two images of the tested specimen with grids on the surface at different tilt angles in an SEM, the 3D surface shape of the specimen can be obtained. Numerical simulation is applied to analyze the feasibility of the proposed method. A validation experiment is performed here. The surface shape of the metal-wire/polymer-membrane structures with thermal deformation is reconstructed. By processing the surface grids of the specimen, the out-of-plane displacement field of the specimen surface is also obtained. Compared with the measurement results obtained by a 3D digital microscope, the experimental error of the proposed method is discussed

A Brief Review on Measurement Methods and Application of Ultra High Pressure Vessels Employed in Food Processing in China

A review of conventional and optical measurement methods of ultra high pressure vessels (UHPVs) in-service was introduced. Typical engineering applications of these technologies were illustrated. The new trends of inspection methods of UHPVs were discussed. Owe to full-field, non-destructive imaging characteristics with high precision and sensitivity, optical measurement methods had gained more and more attention in recent years. Therefore, DIC was suggested to be developed for experimental inspection of UHPVs in 2D or 3D surface shape and deformations.

3D Surface Shape Measurement based on Fringe Projection Techniques

3D Surface Shape Measurement based on Fringe Projection Techniques

Ship Lines Modeling Theory of High-Speed Ship Based on the Partial Differential Equations

Based on the analysis of molded line geometrical characteristic and boundary conditions of high-speed frigate’s hull by using differential geometry, we report a curve modeling principle to express the hull line geometry through differential geometry application. The starting point of this molded-line automatic generation method is using the planar curve to express 3D surface shape. The first problem to be solved is how to get shape functions which describe every design ship curves via the the hull type curves geometry. The second problem to be solved is how the two-dimensional function, which describe ship lines, transformed to the hull shape function designed of three-dimensional hull surface, namely “mathematic ship”.

Skin injury model classification based on shape vector analysis

Background: Skin injuries can be crucial in judicial decision making. Forensic experts base their classification on subjective opinions. This study investigates whether known classes of simulated skin injuries are correctly classified statistically based on 3D surface models and derived numerical shape descriptors.Methods: Skin injury surface characteristics are simulated with plasticine. Six injury classes – abrasions, incised wounds, gunshot entry wounds, smooth and textured strangulation marks as well as patterned injuries - with 18 instances each are used for a k-fold cross validation with six partitions. Deformed plasticine models are captured with a 3D surface scanner. Mean curvature is estimated for each polygon surface vertex. Subsequently, distance distributions and derived aspect ratios, convex hulls, concentric spheres, hyperbolic points and Fourier transforms are used to generate 1284-dimensional shape vectors. Subsequent descriptor reduction maximizing SNR (signal-to-noise ratio) result in an average of 41 descriptors (varying across k-folds). With non-normal multivariate distribution of heteroskedastic data, requirements for LDA (linear discriminant analysis) are not met. Thus, shrinkage parameters of RDA (regularized discriminant analysis) are optimized yielding a best performance with λ = 0.99 and γ = 0.001.Results: Receiver Operating Characteristic of a descriptive RDA yields an ideal Area Under the Curve of 1.0for all six categories. Predictive RDA results in an average CRR (correct recognition rate) of 97,22% under a 6 partition k-fold. Adding uniform noise within the range of one standard deviation degrades the average CRR to 71,3%.Conclusions: Digitized 3D surface shape data can be used to automatically classify idealized shape models of simulated skin injuries. Deriving some well established descriptors such as histograms, saddle shape of hyperbolic points or convex hulls with subsequent reduction of dimensionality while maximizing SNR seem to work well for the data at hand, as predictive RDA results in CRR of 97,22%. Objective basis for discrimination of non-overlapping hypotheses or categories are a major issue in medicolegal skin injury analysis and that is where this method appears to be strong. Technical surface quality is important in that adding noise clearly degrades CRR.Trial registration: This study does not cover the results of a controlled health care intervention as only plasticine was used. Thus, there was no trial registration.

Study of 3D Reconstruction of Laser Welding Pool Surface Based on Shape from Shading

Shape from shading (SFS) is one of the critical techniques in 3D shape recovery in computer vision. The task of SFS is to reconstruct 3D shape of the visible surface of an object from one single picture using its gray variation. Analyzing the 3D shape of welding pool is important to evaluate the welding quality. During the disk laser welding experiments, a high-power laser was used as the auxiliary illuminant, and a high-speed image acquisition system with infrared filter was applied to capture the welding pools in real time. The slant and tilt of illuminant source were estimated by statistics to reconstruct the 3D shape of welding pool visible surface by using the localization method of SFS. Methods of median filter and cubic spline interpolation were used to denoise images and smooth the image shapes. Experimental results showed that the proposed technique could reconstruct parts of welding pool effectively.

Inferring 3D Surface Shape from 2D Contour Curvature

Inferring 3D Surface Shape from 2D Contour Curvature