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Highlights • A topology-based rigid spherical quadrilateral mesh method is proposed in this paper. • The nondifferentiable problem of free-form surface is solved based on topological transformation. • The model of feature extraction for free-form surface based on topological transformation is built. • The tangent bundle of smooth free-form surface manifold is analyzed. Abstract Free-form surface reconstruction is the key technology of mathematical modeling of engineering. It is important for accurate reconstruction of the entity model that conforms to the design. In order to improve the measurement accuracy of the workpiece, a method for free-form surface feature recognition based on topological transformation is proposed in this paper. Firstly, the information of scanning points is expressed as the form of topological space. Based on this, a method of surface constructing that selects the natural-quadratic-surface as the manifold of free-form surface is proposed. Then, the free-form surface that is constructed from the original point cloud is transformed into a smooth free-form surface which is homeomorphic to the original free-form surface based on the theory of topological embedding. The features of the transformed free-form surface can be easily analyzed and recognized. Finally, the qualitative description of an arbitrary point on the surface is obtained by analyzing the tangent bundle of smooth free-form surface manifolds. The feature recognition of free-form surface for workpiece is realized. The experimental results on workpiece model are reported in this paper, which validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Highlights • Shape optimization of shells usually yields structures that are difficult to build. • A shape parametrisation method resulting in PQ-meshes is implemented as a CAD tool. • A comparative study with NURBS modelling illustrates the potential of the method. • Structurally optimal design resulting from the proposed framework are constructible. Abstract The difficulty to construct mechanically optimal shells may limit the use of structural optimisation in practice. The objective of this paper is to propose a new parametric representation of doubly curved shapes suited for structural optimisation of architectural shells that inherently considers fabrication constraints. We focus on a common construction constraint: the covering of building envelopes with planar facets. This paper proposes to implement the so-called marionette technique as a Computer-Aided-Design tool that guarantees covering of free-form shapes with planar quadrilateral facets. General considerations on the size and nature of the optimisation space created with this method are made. It is demonstrated through different case-studies that the quality of the parametrisation for shape optimisation of shell structures is similar to the one offered by Bézier surfaces, an ubiquitous modelling technique. The proposed method conciliates thus fabrication and structural performance. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is the presentation of a technique to be integrated in a numerical airfoil optimization scheme, for the exact satisfaction of a strict equality cross-sectional area constraint.Design/methodology/approach An airfoil optimization framework is presented, based on Area-Preserving Free-Form Deformation (AP FFD) technique. A parallel metamodel-assisted differential evolution (DE) algorithm is used as an optimizer. In each generation of the DE algorithm, before the evaluation of the fitness function, AP FFD is applied to each candidate solution, via coupling a classic B-Spline-based FFD with an area correction step. The area correction step is achieved by solving a sub problem, which consists of computing and applying the minimum possible offset to each one of the free-to-move control points of the FFD lattice, subject to the area preservation constraint.Findings The proposed methodology is able to obtain better values of the objective function, compared to both a classic penalty function approach and a generic framework for handling constraints, which suggests the separation of constraints and objectives (separation-sub-swarm), without any loss of the convergence capabilities of the DE algorithm, while it also guarantees an exact area preservation. Due to the linearity of the area constraint in each axis, the extraction of an inexpensive closed-form solution to the sub problem is possible by using the method of Lagrange multipliers.Practical implications AP FFD can be easily incorporated into any 2D shape optimization/design process, as it is a time-saving and easy-to-implement repair algorithm, independent from the nature of the problem at hand.Originality/value The proposed methodology proved to be an efficient tool in facing airfoil design problems, enhancing the rigidity of the optimal airfoil by preserving its cross-sectional area to a predefined value. [ABSTRACT FROM AUTHOR]

Feature detection on smooth free-form surfaces is much more difficult than that on shapes with sharp features. In this paper, we extract the curved reflection axes (CRAs) of an arbitrary free-form surface as features if they exist. The extraction result is robust to boundary noises and strongly sensitive to extrinsic properties of the surface such as projected normals and curvatures. Compared with the general reflection symmetry, curved reflection symmetry is defined to be a reflection symmetry along a smooth 3D embedded curve instead of a plane, where any point on the curve is a local reflection center for some surface points. The properties of the curved reflection symmetric axis are analyzed, and a novel computational model for detecting and extracting CRAs on free-form surfaces is presented. The experimental results are then compared with both the medial axis and the intrinsic symmetric axis, which are two popular feature representations of 3D shapes, and the advantages and uniqueness of the proposed method are convincingly demonstrated. An application of the proposed method in sweep scanning is also presented. Other applications of the proposed method include feature extraction, shape symmetrization, segmentation, and registration.

Note to Practitioners—This paper was originally motivated by the stylus path planning problem in sweep scanning on curved surfaces (which is a new surface inspection technology), though it is also applicable to shape registration and matching. Traditional coordinate measuring machine inspection of curved surfaces depends heavily on manual intervention, resulting in a very slow and tedious process and the acquired data are prone to inconsistency due to the discontinuous nature of the operation. In contrast, sweep scanning adopts a configuration of a deflectable stylus mounted on a motorized articulating head with two rotary axes inside, which enables the stylus tip to follow a continuous path without having to leave the surface. The head itself is mounted on an xyz table. During a sweep scanning, the head slowly moves on the xyz table (which is heavy and has stringent dynamic constraints due to its large mass) along a nominal path, while the stylus (which is extremely light) quickly oscillates in a direction transverse to the path of the head. The proposed curved reflection axis offers to be a powerful algebraic model for generating a nominal head path for sweep scanning. The reported work is preliminary though, especially in terms of covering the entire surface and also considering the specific length of the stylus, which will be our future work. [ABSTRACT FROM AUTHOR]

Drag reduction has always been the emphasis and difficulty in aircraft design. For a large air freighter or airliner, the induced drag accounts for about 40% of the total drag in the cruise phase. In this case, a robust design for a winglet is implemented to an initial wing of an aircraft. For the purpose of reducing the number of design variables, the NURBS based free form deformation (NURBS-FFD) method is introduced as the parametric method in the winglet design process. An improved particle swarm optimization (PSO) algorithm based on CVTs method is adopted serving as the optimization method for the winglet design. In order to verify the reduction effect on induced drag coefficient, a discrete vortex method is established based on Biot–Savart Law. The optimization results indicate that not only the induced drag coefficient is reduced obviously but also the total drag coefficient is decreased dramatically in the meantime under the situation of the equivalent lift coefficient. [ABSTRACT FROM AUTHOR]

B-splines are commonly utilized to construct the transformation model in free-form deformation (FFD) based registration. B-splines become smoother with increasing spline order. However, a higher-order B-spline requires a larger support region involving more control points, which means higher computational cost. In general, the third-order B-spline is considered as a good compromise between spline smoothness and computational cost. A lower-order function is seldom used to construct the transformation model for registration since it is less smooth. In this research, we investigated whether lower-order B-spline functions can be utilized for more efficient registration, while preserving smoothness of the deformation by using a novel random perturbation technique. With the proposed perturbation technique, the expected value of the cost function given probability density function (PDF) of the perturbation is minimized by a stochastic gradient descent optimization. Extensive experiments on 2D synthetically deformed brain images, and real 3D lung and brain scans demonstrated that the novel randomly perturbed free-form deformation (RPFFD) approach improves the registration accuracy and transformation smoothness. Meanwhile, lower-order RPFFD methods reduce the computational cost substantially. [ABSTRACT FROM AUTHOR]

Motion and deformation are common in prostate diffusion-weighted magnetic resonance imaging (DWI) during acquisition. These misalignments lead to errors in estimating an apparent diffusion coefficient (ADC) map fitted with DWI. To address this problem, we propose an image registration algorithm to align the prostate DWI and improve ADC map. First, we apply affine transformation to DWI to correct intraslice motions. Then, nonrigid registration based on free-form deformation (FFD) is used to compensate for intraimage deformations. To evaluate the influence of the proposed algorithm on ADC values, we perform statistical experiments in three schemes: no processing of the DWI, with the affine transform approach, and with FFD. The experimental results show that our proposed algorithm can correct the misalignment of prostate DWI and decrease the artifacts of ROI in the ADC maps. These ADC maps thus obtain sharper contours of lesions, which are helpful for improving the diagnosis and clinical staging of prostate cancer. [ABSTRACT FROM AUTHOR]

These days, computer-based image registration techniques are increasingly being used in the area of medical imaging as they offer significant benefits for aligning different images together and for visualizing their combined images. However, these techniques require an enormous amount of computation time due to the high resolution and complex nature of the medical images. We propose to alleviate this problem by using a dedicated Network-on-Chip (NoC)-based hardware platform for image registration. This paper describes a novel technique for field-programmable gate array (FPGA) implementation of the B-Spline-based free form deformation (FFD) algorithm, i.e., a widely used algorithm for modeling geometric shapes in a computerized environment. For performance enhancement, we have utilized a lightweight circuit-switched NoC architecture, which is adaptable to most FPGAs. The design description is captured in the Verilog language and implemented using the Xilinx XC2v6000 device at 37MHz. The proposed design is parameterizable at the compile time and supports a wide range of the image resolutions and computational precisions. The experimental results have shown a significant improvement in performance when compared with the other existing hardware implementations of the B-spline-based FFD algorithm. [ABSTRACT FROM AUTHOR]

Abstract: There is an increased interest in social media monitoring to analyse massive, free form, short user-generated text from multiple social media sites such as Facebook, WhatsApp and Twitter. Companies are interested in sentiment analysis to understand customers’ opinions about their products/services. Governments and law enforcement agencies are interested in identifying threats to safeguard their country's national security. They are actively seeking ways to monitor and analyse the public's responses to various services, activities and events, especially since social media has become a valuable real-time resource of information. This study builds on prior work that focused on sentiment classification (i.e., positive, negative). This study primarily aims to design and develop a social sentiment-parsing algorithm for capturing and monitoring an extensive and comprehensive range of emotions from Arabic social media text. The study contributes to the field of sentiment analysis (opinion mining) and can subsequently be used for web mining, cleansing and analytics. [ABSTRACT FROM AUTHOR]

Image registration is an essential technique to obtain point correspondences between anatomical structures from different images. Conventional non-rigid registration methods assume a continuous and smooth deformation field throughout the image. However, the deformation field at the interface of different organs is not necessarily continuous, since the organs may slide over or separate from each other. Therefore, imposing continuity and smoothness ubiquitously would lead to artifacts and increased errors near the discontinuity interface. In computational mechanics, the eXtended Finite Element Method (XFEM) was introduced to handle discontinuities without using computational meshes that conform to the discontinuity geometry. Instead, the interpolation bases themselves were enriched with discontinuous functional terms. Borrowing this concept, we propose a multiresolution eXtented Free-Form Deformation (XFFD) framework that seamlessly integrates within and extends the standard Free-Form Deformation (FFD) approach. Discontinuities are incorporated by enriching the B-spline basis functions coupled with extra degrees of freedom, which are only introduced near the discontinuity interface. In contrast with most previous methods, restricted to sliding motion, no ad hoc penalties or constraints are introduced to reduce gaps and overlaps. This allows XFFD to describe more general discontinuous motions. In addition, we integrate XFFD into a rigorously formulated multiresolution framework by introducing an exact parameter upsampling method. The proposed method has been evaluated in two publicly available datasets: 4D pulmonary CT images from the DIR-Lab dataset and 4D CT liver datasets. The XFFD achieved a Target Registration Error (TRE) of 1.17 ± 0.85 mm in the DIR-lab dataset and 1.94 ± 1.01 mm in the liver dataset, which significantly improves on the performance of the state-of-the-art methods handling discontinuities. [ABSTRACT FROM AUTHOR]

The nonrigid registration algorithm based on B-spline Free-Form Deformation (FFD) plays a key role and is widely applied in medical image processing due to the good flexibility and robustness. However, it requires a tremendous amount of computing time to obtain more accurate registration results especially for a large amount of medical image data. To address the issue, a parallel nonrigid registration algorithm based on B-spline is proposed in this paper. First, the Logarithm Squared Difference (LSD) is considered as the similarity metric in the B-spline registration algorithm to improve registration precision. After that, we create a parallel computing strategy and lookup tables (LUTs) to reduce the complexity of the B-spline registration algorithm. As a result, the computing time of three time-consuming steps including B-splines interpolation, LSD computation, and the analytic gradient computation of LSD, is efficiently reduced, for the B-spline registration algorithm employs the Nonlinear Conjugate Gradient (NCG) optimization method. Experimental results of registration quality and execution efficiency on the large amount of medical images show that our algorithm achieves a better registration accuracy in terms of the differences between the best deformation fields and ground truth and a speedup of 17 times over the single-threaded CPU implementation due to the powerful parallel computing ability of Graphics Processing Unit (GPU). [ABSTRACT FROM AUTHOR]

Paper introduces a 3-D shape representation scheme for automatic face analysis and identification, and demonstrates its invariance to facial expression. The core of this scheme lies on the combination of statistical shape modelling and non-rigid deformation matching. While the former matches 3-D faces with facial expression, the latter provides a low-dimensional feature vector that controls the deformation of model for matching the shape of new input, thereby enabling robust identification of 3-D faces. The proposed scheme is also able to handle the pose variation without large part of missing data. To assist the establishment of dense point correspondences, a modified free-form-deformation based on B-spline warping is applied with the help of extracted landmarks. The hybrid iterative closest point method is introduced for matching the models and new data. The feasibility and effectiveness of the proposed method was investigated using standard publicly available Gavab and BU-3DFE datasets, which contain faces with expression and pose changes. The performance of the system was compared with that of nine benchmark approaches. The experimental results demonstrate that the proposed scheme provides a competitive solution for face recognition. [ABSTRACT FROM AUTHOR]

In order to model complicated folded fabric, this paper proposed a new reverse modeling method. Two kinds of concrete implementation were investigated, which were based on graphical deformation and nonlinear dynamics, respectively. The first method learned from Free-Form Deformation technology is used to form the regular folds, while the element distortion rises. The second method adopts a fluid structure interaction algorithm to form the irregular folds. Both methods can transform the finite element model from expanded state to initial folded state without changing the mesh topology. Therefore, the mapping relationship between the finite element models of expanded state and folded state can be naturally obtained. Then, the initial stress used to modify the model can be calculated according to the mapping relationship, and the modifying can ensure the accordance of inflated flexible fabric’s geometry and the original design. At last, the finite element model of an inflatable fabric, which cannot be modeled by exiting method, was established by the new reverse modeling method with its feasibility and accuracy verified by comparing the calculation results. The results of this study could provide a reference for modeling complicated folded fabric. [ABSTRACT FROM AUTHOR]

The contour following task of a multi-axis servo system is one of the most important applications of modern Computer Numerical Control (CNC) machine tools, and is widely seen in many types of CNC machining. Hence, the reduction of contour error occurring in the contour following process is paramount and deserves more comprehensive investigation. In general, the calculation of precise contour error in real time is very challenging if not impossible, in free-form curve following tasks. To deal with such a problem, this paper proposes six real-time contour error estimation methods for free-form parametric curves. The feasibility of these methods is verified with several NURBS parametric curve contour following experiments. In addition, experimental results reveal that the proposed methods can provide more accurate contour error estimation for various free-form curves than the other estimation algorithms tested in the experiments. With the proposed contour error estimation approach, advanced motion control schemes can be designed to efficiently reduce contour errors of contour following tasks. [ABSTRACT FROM AUTHOR]

The accurate and fast prediction of cutting forces in five-axis milling of free-form surfaces remains a challenge due to difficulties in determining the varying cutter-workpiece engagement (CWE) boundaries and the instantaneous uncut chip thickness (IUCT) along the tool path. This paper proposes an approach to predict the cutting forces in five-axis milling process with a general end mill considering the cutter runout effect that is inevitable in the practical machining operations. Based on the analytical model of cutting edge combined with runout parameters, the expression of the rotary surface formed by each cutting edge undergoing general spatial motion is firstly derived. Then by extracting the feasible contact arc along the tool axis, a new arc-surface intersection method is developed to determine the CWE boundaries fast and precisely. Next, the circular tooth trajectory (CTT) model is developed for the calculation of the IUCT with a slight sacrifice of accuracy. In comparison with the true IUCT calculated by the trochoidal tooth trajectory model, the approximation error introduced by the circular assumption is negligible while the computational efficiency improves a lot. Finally, combining with the calibrated cutting coefficients and runout parameters, comprehensive formulation of the cutting force system is set up. Simulations and experimental validations of a five-axis flank milling process show that the novel CTT model possesses obvious advantages in computing efficiency and accuracy over the existing approaches. Rough machining of a turbo impeller is further carried out to test the practicability and effectiveness of the proposed mechanistic model. [ABSTRACT FROM AUTHOR]

In an accurate free-form deformation of a polygonal object, only the linear geometry, e.g., triangles or planar polygons, is deformed as triangular Bézier patches or trimmed tensor product Bézier patches; the related normal field is not considered. Thus, the geometry appearance and shading of the deformed object are typically not smooth. In this paper, both the linear geometry and normal of a polygonal object are simultaneously considered in the framework of accurate free-form deformation. First, each triangle and its normal field are deformed as two cubic triangular Bézier patches. Then, the curved geometry corresponding to the deformed triangles is locally adjusted to tone the smoothness of the geometry appearance according to the deformed normal field. The deformed normal field is adjusted accordingly. As a result, a smooth free-form deformation with visually plausible smooth geometry and shading is obtained. Furthermore, the sharp features in the polygonal object can be preserved. Because the curved geometry and normal field adjustments are local operations, all of the above computations can be performed in parallel on a GPU. The experimental results show that the method can deform a complex polygonal object as a smooth object in real time while preserving sharp features. [ABSTRACT FROM AUTHOR]

This paper discusses the important role of human-computer interaction in computer aided inspected points planning process, and put forward the technical requirements of inspected points planning system must have in order to achieve the full capacity of human-computer interaction. Using second-development platform of UG, we designed a framework of computer aided inspected points planning system which can fully carry out human-computer interaction. Then we proposes two planning strategy which can fully meet the human-computer interaction requirements. [ABSTRACT FROM AUTHOR]

Recently the authors presented a two-phase genetic algorithm (GA) for minimum weight design of free-form steel space-frame roof structures consisting of discrete commercially available rectangular hollow structural sections (HSS). Subsequently the algorithm was extended to topology optimization of structures. This article presents a new methodology for simultaneous sizing, topology, and shape optimization of free-form steel space-frame roof structures with complex geometries using evolutionary computing. Two methods of altering the geometry of the structure are presented, one a simple method to be used for roof structures with relatively regular geometries, and the other for more complicated geometries. The goal is to achieve additional structural efficiencies by altering the geometry of the roof structure while simultaneously optimizing the roof member and column cross-sectional dimensions and the roof topology. Esthetics is a significant consideration in the structures of the type considered in this research. As such, preserving the general form created by the architect is considered in the proposed shape optimization algorithm. To achieve this, heuristic limits are imposed to avoid drastic or undesirable changes in their architectural form. The methodology is applied to two real-life free-form steel space-frame roof structures. They are two of the thirteen train stations making up the Ottawa Light Rail Transit (OLRT) system to be completed in Ottawa, Canada, in 2018. Efficiencies in the range of 10–16% are reported for the two examples. [ABSTRACT FROM AUTHOR]

The aerodynamic optimization design of typical transport afterbody considering the influence of the wing wake flow is studied. An optimization framework is established for the aircraft configuration and used for afterbody optimization at cruising status. The objective of this framework is to optimize the afterbody considering the influence from other parts of aircraft and the engineering constraints simultaneously. The spatial property of the afterbody in spatial control frame is established by implementing the free form deformation (FFD) approach. The NURBS spline is chosen as the basis function, which can represent the property of spatial control element and is suitable for afterbody geometry. Infinite interpolation deforming grid technique is adopted to update spatial grid with high efficiency and mesh quality. The modified Kriging surrogate model and quantum particle swarm algorithm are included in the optimization system to increase efficiency and ability to find global optimal solution. In order to reduce drag at cruising status, upswept angle and cross section shape are optimized as the main afterbody configuration parameters. The result of the case shows that the aerodynamic performance of the transport' s body is improved after the optimization. [ABSTRACT FROM AUTHOR]

This study investigates a new non-rigid registration method based on Huber prior. The goal of image registration is to find a biologically plausible transformation which results in the spatial alignment of structurally or functionally corresponding regions in the two images. In order to improve the computing efficiency and registration precision, we used B-spline based free-form deformation (FFD) model. Our innovation is using Huber prior as penalty term of the energy function for better results. The FFD model with Huber prior which has high accuracy and strong robustness can settle the over-smoothing and edge information deficiency. We applied the proposed algorithm to both simulated data and real data registrations. Distinctly, the experiment results show that our method gets better results compared to conventional FFD registration algorithms. [ABSTRACT FROM AUTHOR]

Future mobile and wearable devices are heavily influenced by advances in materials which make the devices flexible to interact. In this paper, we propose a system to capture the shape of bent device at graphics framework and make use of the shape to develop novel user interactions for native and app store downloadable applications on consumer electronic devices. We further detail the API, parameters and prototype on Android for shape generation along with OpenGL based emulation for bendable device deformation, followed by usability study results. [ABSTRACT FROM AUTHOR]

This article presents a new approach for finishing free-form surfaces on three-axis computer numerical control (CNC) milling machines using ball-end mill tools. The proposed approach includes four stages and it is based on the localisation of local shapes composing the surfaces. In the first stage, the surfaces are triangulated semi-adaptively. In the second stage, the triangles having the same local shape are grouped into distinct sub-regions (concave developable, concave, convex developable, convex, planar and saddle) and the associated theoretical tool radius is calculated. In the third stage, the final optimum tools are determined and an assignment mode of tools is proposed. In the final stage, the optimum machining strategy for each sub-region is selected and finally the tool path is generated. The proposed approach has been tested in simulation over several free-form surfaces and the results show that it is efficient, especially when the surfaces are composed of many different local shapes. [ABSTRACT FROM AUTHOR]

Ultra-precision machine errors are generally carried out by laser interferometer measurement preliminary, and then, judgment is further made by trial cutting parts. The applications are limited due to its high cost and the unavailable measurement data in the non-open source ultra-precision machines. Meanwhile, the machining parts are lack of an arithmetic that tells the main errors of the processing. This article first analyzes the specific forms of machine errors, and the model of geometric errors has been simplified based on the dynamics of multibody systems theory. On the basis of the coupling geometric errors, specific shapes are used to reverse calculate errors, and the result could predict the processing conditions in different free form surfaces. The accuracy of reverse calculation model is verified by experiments. [ABSTRACT FROM AUTHOR]

In this paper, volumetric b-splines are employed to deform the aerodynamic surface. The geometry is enclosed in a volumetric parallelepiped, referred to as control box, which in, essence, is similar to Free Form Deformation (FFD). The use of generic volumetric b-splines requires to calculate the parametric coordinates, but offers some important advantages over other parameterization techniques, such as deformation locality. This parameterization can be applied to the design of complex three-dimensional configurations and also offers the possibility to incorporate the geometric description extracted from the Computational Aid Design (CAD) files, which most frequently are in the form of Non-Uniform Rational B-Splines (NURBS), in what we call multilevel deformation; that is, the control box deforms the NURBS, while the NURBS deforms the computational grid, following the chain rule. In this work, a volumetric b-spline parameterization has been applied in an automatic gradient-based optimization strategy in order to optimize the aerodynamic surface of aeronautical configurations. The design variables are the control points, while the gradients are calculated using the continuous adjoint formulation. [ABSTRACT FROM AUTHOR]

Abstract: A two-phase genetic algorithm is presented for simultaneous sizing and topology optimization of free-form steel space frame roof structures consisting of discrete commercially available rectangular hollow structural sections. The algorithm is applied to two real-life space roof structures intended for Ottawa Light Rail Transit (OLRT). It is shown that the algorithm is effective for topology optimization of real-life roof structures with complex curvatures in multiple planes. [Copyright &y& Elsevier]

Die modernen digitalen Planungstools erlauben es nicht nur, komplexe frei geformte Baukörper mit überschaubarem Aufwand zu realisieren, sondern auch einzelne, klassischerweise seriell gefertigte Bauteile wie Fassadenelemente - parametrisch beschrieben - lokal zu differenzieren. Die Informierung der Geometrie mit energierelevanten Daten wie Wärmeeintrag, Solargewinne oder Lichtausbeute führen dabei durch rein passive (geometrische) Maßnahmen zu effizienteren Gebäuden. Das von FAT LAB in Zusammenarbeit mit Schüco entwickelte Elementfassadensystem 'Parametric Concept' steht für einen gesamtheitlichen Systemansatz, in dem das Prinzip des 'Mass Customization' von der digitalen Planung bis hin zur Fertigung und Montage konsequent umgesetzt wird. Parametric façade system. As well as allowing for the construction of complex free-form Buildings, modern CAD-tools also make use of parametric principles to locally differentiate components such as facade elements which are traditionally manufactured in a classical serial manner. Their geometry can be informed with energetically relevant data like heat load, solar gains and daylight yield and therefore improve the building performance by applying passive (geometric) measures. 'Parametric Concept' is an element facade system developed by FAT LAB in cooperation with Schüco. It represents a fully integrated, systematic approach to façade realisation, implementing principles of mass-customization into every step of the process from CAD planning to digital manufacturing and product assembly. [ABSTRACT FROM AUTHOR]

Abstract: In nonrigid image registration, similarity measures including spatial information have been shown to perform better than those measures without spatial information. In this work, we provide new insight to the relationships among regional mutual information, regional probability distribution functions (PDFs) and global PDFs, and propose a novel nonrigid registration scheme with spatially weighted global probability distribution function (SWGPDF). Similarity measures based on SWGPDF (SWGPDFSM) are constructed. Three different spatial sub-region division methods are compared: the equally spaced sub-region (ESSR), the local binary pattern sub-region (LBPSR) and the gradient sub-region (GSR). The registration scheme applies B-spline based free form deformations (FFDs) as the transformation model. A Parzen window and linear interpolation are used to construct histograms. The SWGPDFSM registration scheme with ESSR space division is compared with the traditional global mutual information (gMI), the traditional global normalized mutual information (gNMI), regional mutual information and the SWGPDFSM with LBPSR or GSR space division. The test results show that SWGPDFSM scheme with ESSR space division outperforms the other schemes for elastically aligning images in the presence of big geometrical transformations, bias fields and illumination changes. [Copyright &y& Elsevier]

Highlights: [•] A registration technique based on low rank – sparse data decomposition is introduced. [•] Registration is applied to dynamic contrast enhanced MRI. [•] Errors in the monitoring of enhancement in dynamic contrast enhanced MRI are reduced. [ABSTRACT FROM AUTHOR]

Abstract: Super-resolution (SR) reconstruction is an effective method to solve the problem, that the face image resolution is too low to be recognized in video, but the non-rigid change of deformed face and expression changes greatly affect the accuracy of registration and reconstruction. To solve these problems, a method of multi-level model free form deformation (FFD) elastic registration algorithm based on B spline is proposed. It first use low-resolution FFD grid for global registration, to emphasize the contribution of edge information for registration, we introduce edge registration measure into the sum of squared difference (SSD) criterion. Then divide the global registration image and reference image into a series of corresponding sub-image pairs and calculate the correlation coefficient of each pair; at the same time, we do local registration with high-resolution FFD grid to the small value correlation coefficient sub-image pairs. In the registration process of optimization, the paper uses adaptive step length gradient descent method algorithm based on chaotic variables to improve optimization efficiency. After registration, the algorithm of project onto convex sets (POCS) is used to reconstruct SR face image through several low resolution image sequences, and then recognized these SR face images by support vector machines (SVM) classifier. Experimental results from standard video database and self-built video database show that this method can register and reconstruct face image accurately in the condition of great face deformation and expression change, while the face recognition accuracy is also improved. [Copyright &y& Elsevier]

A long-standing problem in marker-based facial motion capture is what are the optimal facial mocap marker layouts. Despite its wide range of potential applications, this problem has not yet been systematically explored to date. This paper describes an approach to compute optimized marker layouts for facial motion acquisition as optimization of characteristic control points from a set of high-resolution, ground-truth facial mesh sequences. Specifically, the thin-shell linear deformation model is imposed onto the example pose reconstruction process via optional hard constraints such as symmetry and multiresolution constraints. Through our experiments and comparisons, we validate the effectiveness, robustness, and accuracy of our approach. Besides guiding minimal yet effective placement of facial mocap markers, we also describe and demonstrate its two selected applications: marker-based facial mesh skinning and multiresolution facial performance capture. [ABSTRACT FROM PUBLISHER]

Abstract: Solid shape is typically segmented into surface regions to define the appearance and function of parts of the shape; these regions in turn use curve networks to represent boundaries and creases, and feature points to mark corners and other shape landmarks. Conceptual modeling requires these multi-dimensional nested structures to persist throughout the modeling process, an aspect not supported, up to now, in free-form sculpting systems. We present the first shape sculpting framework that preserves and controls the evolution of such nested shape features. We propose a range of geometric and topological behaviors (such as rigidity or mutability) applied hierarchically to points, curves or surfaces in response to a set of typical free-form sculpting operations, such as stretch, shrink, split or merge. Our method is illustrated within a free-form sculpting system for self-adaptive quasi-uniform polygon meshes, where geometric and topology changes resulting from sculpting operations are applied to points, edges and triangular facets. We thus facilitate, for example, the persistence of sharp features that automatically split or merge with variable rigidity, even when the shape changes genus. Sculpting nested structures expands the capabilities of most conceptual design workflows, as exhibited by a suite of models created by our system. [Copyright &y& Elsevier]

Abstract: This paper investigates the consistent stabilizability of switched Boolean networks (SBNs) by using the semi-tensor product method, and presents a number of new results. First, an algebraic expression of SBNs is obtained by the semi-tensor product, based on which the consistent stabilizability is then studied for SBNs and some necessary and sufficient conditions are presented for the design of free-form and state-feedback switching signals, respectively. Finally, the consistent stabilizability of SBNs with state constraints is considered and some necessary and sufficient conditions are proposed. The study of illustrative examples shows that the new results obtained in this paper are very effective in designing switching signals for the consistent stabilizability of SBNs. [Copyright &y& Elsevier]

There are various techniques for deforming three-dimensional objects in existing computer-aided design (CAD) systems. To maintain user-specified constraints in the deformation of a parametric and feature-based model is a new challenge in deformation modelling. This article presents a constraint-based deformation technique. Firstly, a deformed object is obtained with common deformation techniques such as free-form deformation (FFD) and axial deformation. Secondly, features defined with parametric are grouped into systems of primitive constraints based on user specification. Finally, features are reconstructed by the use of optimisation technique. The optimisation is to minimise the changes in the deformed model subjected to all the provided constraints. This method allows deformations like FFD and axial deformation to be performed without destroying the constraints in the model. This method combines the advantage of free-form modelling with feature-based modelling and allows engineering design to be performed in a free-form manner. [ABSTRACT FROM AUTHOR]

Highlights: [•] We propose a registration scheme that is enhanced by a statistical model. [•] Registration is performed on MR images of 17 patients with cervical cancer. [•] Compared to conventional registration segmentation of the evaluated structure is improved. [ABSTRACT FROM AUTHOR]

Unlike FEM (Finite Element Method), which provides an accurate deformation of soft objects, FFD (Free Form Deformation) based methods have been widely used for a quick and responsive representation of deformable objects in real-time applications such as computer games, animations, or simulations. The FFD-AABB (Free Form Deformation Axis Aligned Bounding Box) algorithm was also suggested to address the collision handling problems between deformable objects at an interactive rate. This paper proposes an enhanced FFD-AABB algorithm to improve the frame rate of simulation by adding the bounding sphere based collision test between 3D deformable objects. We provide a comparative analysis with previous methods and the result of proposed method shows about an 85% performance improvement. [ABSTRACT FROM AUTHOR]

Free-form deformation (FFD) is a method first introduced within the graphics industry to enable flexible deformation of geometric models. FFD uses an R3 to R3 mapping of a defomiable space to the global Cartesian space to produce the geometry deformation. This method has been extensively used within the design optimisation field as a shape parameterisation technique. Typically it has been used to parametense analysis meshes, where new design geometries are produced by deforming the original mesh. This method allows a concise set of design variables to be used while maintaining a flexible shape representation. However, if a computer aided design (CAD) model of the resulting geometry is required, reverse engineering techniques would need to be utilised to recreate the model irom the deformed mesh. This paper extends the use of FFD within an optimisation routine by using FFD to directly parametense a CAD geometry. Two methods of linking the FFD methods with the CATIA V5 CAD package are presented. Each CAD integration technique is then critiqued with respect to shape optimisation. Finally the set-up and initialisation of a case study is illustrated. The case study chosen is the aerodynamic optiinisation of the wing-fiiselage junction of a typical passenger aircraft. [ABSTRACT FROM AUTHOR]

A computer vision system is described that captures color image sequences, detects and recognizes static hand poses (i.e., "letters:) and interprets pose sequences in terms of gestures (i.e., "words"). The hand object is detected with a double-active contour-based method. A tracking of the hand pose in a short sequence allows detecting "modified poses", like diacritic letters in national alphabets. The static hand pose set corresponds to hand signs of a thumb alphabet. Finally, by tracking hand poses in a longer image sequence, the pose sequence is interpreted in terms of gestures. Dynamic Bayesian models and their inference methods (particle filter and Viterbi search) are applied at this stage, allowing a bi-driven control of the entire system. [ABSTRACT FROM AUTHOR]

Abstract: Free-Form Deformation Techniques (FFD) are commonly used to generate animations, where a polygonal approximation of the final object suffices for visualization purposes. However, for some CAD/CAM applications, we need an explicit expression of the object, rather than a collection of sampled points. If both object and deformation are polynomial, their composition yields a result that is also polynomial, albeit very high degree, something undesirable in real applications. To solve this problem, we transform each curve or surface composing the object, usually expressed in the Bernstein basis, to a modified Newton form. In this representation, the two-point analogue of Taylor expansions, the composition admits a simple expression in terms of discrete convolutions, and degree reduction corresponding to Hermite approximation is trivial by dropping high-degree coefficients. Furthermore, degree-reduction can be incorporated into the composition. Finally, the deformed curve or surface is converted back to the Bernstein form. This method extends to general non-polynomial deformation, such as bending and twisting, by computing a polynomial approximant of the deformation. [Copyright &y& Elsevier]

This paper presents an algorithm for improving the interpolation accuracy in turning operations. The parts considered are formed by revolving a free-form profile which is implemented in terms of Bézier formulation around a center linear axis. The demand for the manufacturing of such geometric shapes is frequently met in parts produced by casting and forging methods. The method employs a computer numerical control (CNC) turning machine and is based on the locus tracing concept. The algorithm described utilizes a real-time CNC interpolator providing the highest possible accuracy of which the turning machine is capable. The whole machining task can be programmed as a canned cycle, essentially extending the feature generating capabilities of the existing G70/G73 CNC turning fixed cycles. [ABSTRACT FROM AUTHOR]

This paper proposes a topology-preserving multiresolution elastic registration method based on a discrete Markov random field of deformations and a block-matching procedure. The method is applied to the object-based interpolation of tomographic slices. For that purpose, the fidelity of a given deformation to the data is established by a block-matching strategy based on intensity- and gradient-related features, the smoothness of the transformation is favored by an appropriate prior on the field, and the deformation is guaranteed to maintain the topology by imposing some hard constraints on the local configurations of the field. The resulting deformation is defined as the maximum a posteriori configuration. Additionally, the relative influence of the fidelity and smoothness terms is weighted by the unsupervised estimation of the field parameters. In order to obtain an unbiased interpolation result, the registration is performed both in the forward and backward directions, and the resulting transformations are combined by using the local information content of the deformation. The method is applied to magnetic resonance and computed tomography acquisitions of the brain and the torso. Quantitative comparisons offer an overall improvement in performance with respect to related works in the literature. Additionally, the application of the interpolation method to cardiac magnetic resonance images has shown that the removal of any of the main components of the algorithm results in a decrease in performance which has proven to be statistically significant. [ABSTRACT FROM AUTHOR]

Subdivision surfaces allow smooth free-form surface modelling without topological constraints. They have become a fundamental representation for smooth geometry, particularly in the animation and entertainment industries. This survey summarizes research on subdivision surfaces over the last 15 years in three major strands: analysis, integration into existing systems and the development of new schemes. We also examine the reason for the low adoption of new schemes with theoretical advantages, explain why Catmull-Clark surfaces have become a de facto standard in geometric modelling, and conclude by identifying directions for future research. [ABSTRACT FROM AUTHOR]

Diffusion tensor imaging (DTI) is a non-invasive technique used to obtain the 3D fiber structure of whole human hearts, for both in vivo and ex vivo cases. However, by essence, DTI does not measure directly the orientations of myocardial fibers. In contrast, polarized light imaging (PLI) allows for physical measurements of fiber orientations, but only for ex vivo case. This work aims at quantitatively comparing the myocardial fiber orientations of whole human hearts obtained from cardiac DTI with those measured by PLI. Whole human neonatal and infant hearts were first imaged using DTI. The same whole hearts were then imaged using PLI. After DTI and PLI data are registered, the orientations of fibers from the two imaging modalities were finally quantitatively compared. The results show that DTI and PLI have similar variation patterns of elevation and azimuth angles, with some differences in transmural elevation angle range. DTI itself induces an underestimation of the range of transmural elevation angles by a factor of about 25° at the basal and equatorial slices and the reduction of spatial resolution further decreases this range. PLI data exhibit a 15°  ±  5° (P  <  0.01) narrower transmural elevation angle range at apical slices than in basal or equatorial slices. This phenomenon is not observed in DTI data. In both modalities, the azimuth angle maps exhibit curved or twisting boundaries at the basal and apical slices. The experimental results globally enforce DTI as a valid imaging technique to reasonably characterize fiber orientations of the human heart noninvasively. [ABSTRACT FROM AUTHOR]