Tsz Ho Kwok - In/Before 2016

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In/Before 2016

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A Structural Topology Design Method Based on Principal Stress Line

Tsz-Ho Kwok, Yongqiang Li, and Yong Chen
Computer-Aided Design, Volume 80, November 2016, Pages 19-31.
[PDF][doi:10.1016/j.cad.2016.07.005][video]

Abstract:
Topology optimization is an important topic in structural mechanics. One common application is to obtain the optimal distribution of material that maximizes the stiffness of the solution (minimize the compliance). However, as an iterative process, topology optimization of large and complex structures is computationally intensive. The problem becomes even more complicated if the manufacturing constraints are taken into account in the optimization process. In this paper, a novel growth method based on Principal Stress Lines (PSLs) is presented for topology optimization. The PSLs are traced in the design domain along the direction of principal stresses, in which the materials would be located to define the geometry and topology of the structure. Consequently, the optimization problem is converted into a geometric design problem. Compared to previous methods, the computation based on PSLs is fast, and the designer can have explicit control over the number of structural members. In addition, the manufacturing constraints can easily be incorporated. Multiple test cases are given to illustrate the presented method. The PSL-based method is promising for building practical designing tools for various structural applications.

Rope Caging and Grasping

Tsz-Ho Kwok, Weiwei Wan, Jia Pan, Jianjun Yuan, Kensuke Harada, Charlie C.L. Wang, and Yong Chen
IEEE The International Conference on Robotics and Automation (ICRA), May 16-21, 2016, Stockholm, Sweden.
[PDF][doi:10.1109/ICRA.2016.7487345][video][Dataset]

Abstract:
We present a novel method for caging grasps in this paper by stretching ropes on the surface of a 3D object. Both topology and shape of a model to be grasped has been considered in our approach. Our algorithm can guarantee generating local minimal rings on every topological branches of a given model with the help of a Reeb graph. Cages and grasps can then be computed from these rings, and physical experimental tests have been conducted to verify the robustness of our approach.

Geometric Analysis and Computation Using Layered Depth-Normal Images for Three-Dimensional Microfabrication

Tsz-Ho Kwok, Yong Chen, and Charlie C.L. Wang
Three-Dimensional Microfabrication Using Two-photon Polymerization, In Micro and Nano Technologies, William Andrew Publishing, 2016, Chapter 5, Pages 119-147.
[PDF][doi:10.1016/B978-0-323-35321-2.00007-8][LDNI-based Solid Modeling]

Abstract:
Additive manufacturing (AM) is a direct manufacturing process that provides the ability to fabricate parts with complex shape. Robust geometric computation is essential to deal with the complex geometry. Current geometric computation methods based on the boundary representation (B-rep) explicitly define and compute geometry. However, such approaches lack in simplicity and are prone to robustness problems. In this chapter, a point-based geometric computation method based on the Layered Depth-Normal Image (LDNI) is presented. A set of computation algorithms are developed for this new point-based method, including the conversions between the LDNI and B-rep models, the offsetting and the Boolean geometric operations, etc. A number of test cases has shown the robustness of the developed geometric operations, and a set of Computer-Aided Design and Manufacturing (CAD/CAM) applications related to the complex component design and manufacturing has also been explored.

Styling Evolution for Tight-Fitting Garments

Tsz-Ho Kwok, Yanqiu Zhang, Charlie C.L. Wang, Yong-Jin Liu, and Kai Tang
IEEE Transactions on Visualization and Computer Graphics, vol. 22, no. 5, pp. 1580-1591, May 1 2016.
[PDF][doi:10.1109/TVCG.2015.2446472][video][project page]

Abstract:
We present an evolution method for designing the styling curves of garments. The procedure of evolution is driven by aesthetics-inspired scores to evaluate the quality of styling designs, where the aesthetic considerations are represented in the form of streamlines on human bodies. A dual representation is introduced in our platform to process the styling curves of designs, based on which robust methods for realizing the operations of evolution are developed. Starting from a given set of styling designs on human bodies, we demonstrate the effectiveness of set evolution inspired by aesthetic factors. The evolution is adaptive to the change of aesthetic inspirations. By this adaptation, our platform can automatically generate new designs fulfilling the demands of variations in different human bodies and poses.

Four-Dimensional Printing for Freeform Surfaces: Design Optimization of Origami and Kirigami Structures

Tsz-Ho Kwok, Charlie C.L. Wang, Dongping Deng, Yunbo Zhang, and Yong Chen
ASME Transactions - Journal of Mechanical Design, 137(11), 111413 (Oct 12, 2015).
[PDF][doi:10.1115/1.4031023][video][Spotlight]

Abstract:
A self-folding structure fabricated by additive manufacturing can be automatically folded into a demanding 3D shape by actuation mechanisms such as heating. However, 3D surfaces can only be fabricated by self-folding structures when they are flattenable. Most generally designed parts are not flattenable. To address the problem, we develop a shape optimization method to modify a non-flattenable surface into flattenable. The shape optimization framework is equipped with topological operators for adding interior/boundary cuts to further improve the flattenability. When inserting cuts, self-intersection is locally prevented on the flattened 2D pieces. The total length of inserted cuts is also minimized to reduce artifacts on the finally folded 3D shape.

Improvements to the ICP Algorithm for Shape Registration in Manufacturing

Tsz-Ho Kwok, and Kai Tang
ASME Journal of Manufacturing Science and Engineering, 138(1), 011014 (Sep 09, 2015).
[PDF][doi:10.1115/1.4031335]

Abstract:
Iterative Closest Point (ICP) is a popular algorithm used for shape registration while conducting inspection during a production process. A crucial key to the success of ICP is the choice of point selection method. While point selection can be customized for a particular application using its prior knowledge, Normal-Space Sampling is commonly used when normal vectors are available. Normal-based approach can be further improved by stability analysis - called covariance sampling. The stability analysis should be accurate to ensure the correctness of covariance sampling. In this paper, we go deep into the details of covariance sampling, and propose a few improvements for stability analysis. We theoretically and experimentally show that these improvements are necessary for further success in covariance sampling. Experimental results show that the proposed method is more efficient and robust for the ICP algorithm.

Volumetric Template Fitting for Human Body Reconstruction from Incomplete Data

Tsz-Ho Kwok, Kwok-Yun Yeung, and Charlie C.L. Wang
Journal of Manufacturing Systems, Volume 33, Issue 4, October 2014, Pages 678–689.
[PDF][doi:10.1016/j.jmsy.2014.05.009][video][project page]

Abstract:
In this paper, we present a method for reconstructing 3D human body from incomplete data, which are point clouds captured by inexpensive RGB-D cameras. Making use of the volumetric mesh in a template, the fitting process is robust. This method produces high quality fitting results on incomplete data, which are hard to be offered by the surface fitting based methods. The method is formulated as an optimization procedure, so that the results of volumetric fitting rely on the quality of initial shape (i.e., the shape of template). In order to find a good initial shape, we develop a template selection algorithm to choose a template in an iterative manner by using the statistical models of human bodies. Experimental results show that our method can successfully reconstruct human body with less than 1% anthropometry measurement error.

Shape Optimization for Human-Centric Product with Standardized Components

Tsz-Ho Kwok, and Charlie C.L. Wang
Computer-Aided Design, Volume 52, July 2014, Pages 40-50.
[PDF][doi:10.1016/j.cad.2014.03.002][video]

Abstract:
In this paper, we present an optimization framework for automating the shape customization of human-centric products, which can be mounted on or embedded in human body (such as exoskeletal devices and implants). This kind of products needs to be customized to fit the body shapes of users. At present, the design customization for freeform objects is often taken in an interactive manner that is inefficient. We investigate a method to automate the procedure of customization. Major difficulty in solving this problem is caused by the not freely changed shape of components. They should be selected from a series of standardized shapes. Different from the existing approaches that allow fabricating all components by customized production, we develop a new method to generate customized products by using as-many-as-possible standardized components. Our work is based on a mixed-integer shape optimization framework.

Domain Construction for Volumetric Cross-Parameterization

Tsz-Ho Kwok, and Charlie C.L. Wang
Computers & Graphics, Special Issue of CAD/Graphics 2013, November 16-18, 2013, Hong Kong, Volume 38, February 2014, Pages 86-96. Acceptance rate: 9% (31/344).
[PDF][doi:10.1016/j.cag.2013.10.026][Best Paper Honorable Mention] [Dataset]

Abstract:
We present an algorithm in this paper for constructing volumetric domains with consistent topology to parameterize three-manifold solid models having homeomorphic topology. The volumetric parameterizations generated by our approach share the same set of base domains and are constrained by the corresponding anchor points. Our approach allows users to control interior mappings by specifying interior anchor points, and the anchor points are interpolated exactly. With the help of a novel construction algorithm developed in this work, the volumetric cross-parameterization computed by our method demonstrates its functionality in several examples.

Improved skeleton tracking by duplex Kinects: a practical approach for real-time applications

Kwok-Yun Yeung, Tsz-Ho Kwok, and Charlie C.L. Wang
ASME Transactions - Journal of Computing and Information Science in Engineering, 13(4), 041007 (Oct 16, 2013).
[PDF][doi:10.1115/1.4025404][video]

Abstract:
Recent development of per-frame motion extraction method can generate the skeleton of human motion in real-time with the help of RGB-D cameras such as Kinect. This leads to an economic device to provide human motion as input for real-time applications. As generated by a single-view image plus depth information, the extracted skeleton usually has problems of unwanted vibration, bone-length variation, self-occlusion, etc. This paper presents an approach to overcome these problems by synthesizing the skeletons generated by duplex Kinects, which capture the human motion in different views. The major technical difficulty of this synthesis comes from the inconsistency of two skeletons. Our algorithm is formulated under the constrained optimization framework by using the bone-lengths as hard constraints and the tradeoff between inconsistent joint positions as soft constraints. Schemes are developed to detect and re-position the problematic joints generated by per-frame method from duplex Kinects. As a result, we develop an easy, cheap and fast approach that can improve the skeleton of human motion at an average speed of 5ms per frame.

Constructing Common Base Domains by Cues from Voronoi Diagram

Tsz-Ho Kwok, Yunbo Zhang, Charlie C.L. Wang
Graphical Models, Special Issue of 2012 Geometric Modeling and Processing (GMP) conference, June 20-22, 2012, Mount Huang, Volume 74, Issue 4, July 2012, Pages 152-163.
[PDF][doi:10.1016/j.gmod.2012.03.012][project page]

Abstract:
In this paper, we propose a novel algorithm to construct common base domains for cross-parameterization constrained by anchor points. Based on the common base domains, a bijective mapping between given models can be established. Experimental results show that the distortion in a cross-parameterization generated on our common base domains is much smaller than that of a mapping on domains constructed by prior methods. Different from prior algorithms that generate domains by a heuristic of having higher priority to link the shortest paths between anchor points, we compute the surface Voronoi diagram of anchor points to find out the initial connectivity for the base domains. The final common base domains can be efficiently generated from the initial connectivity. The Voronoi diagram of the anchor points gives better cues than the heuristic of connecting shortest paths greedily, therefore resulting in an efficient and reliable algorithm for construction of common base domains that bring to low distortion in constrained cross-parameterization.

Efficient Optimization of Common Base Domains for Cross-Parameterization

Tsz-Ho Kwok, Yunbo Zhang, Charlie C.L. Wang
IEEE Transactions on Visualization and Computer Graphics, vol.18, no.10, pp.1678-1692, Oct. 2012
[PDF][doi:10.1109/TVCG.2011.115][project page]

Abstract:
Given a set of corresponding user-specified anchor points on a pair of models having similar features and topologies, the cross-parameterization technique can establish a bijective mapping constrained by the anchor points. In this paper, we present an efficient algorithm to optimize the complexes and the shape of common base domains in cross-parameterization for reducing the distortion of the bijective mapping. The optimization is also constrained by the anchor points. We investigate a new signature, Length-Preserved Base Domain (LPBD), for measuring the level of stretch between surface patches in crossparameterization. This new signature well balances the accuracy of measurement and the computational speed. Based on LPBD, a set of metrics are studied and compared. The best ones are employed in our domain optimization algorithm that consists of two major operators, boundary swapping and patch merging. Experimental results show that our optimization algorithm can reduce the distortion in cross-parameterization efficiently.

Exemplar-Based Statistical Model for Semantic Parametric Design of Human Body

Chih-Hsing Chu, Ya-Tien Tsai, Charlie C.L. Wang, and Tsz-Ho Kwok
Computers in Industry, vol.61, no.6, pp.541-549, August 2010.
[PDF][doi:10.1016/j.compind.2010.03.004] [PCA on Human Body Database]

Abstract:
This paper presents an exemplar-based method to provide intuitive way for users to generate 3D human body shape from semantic parameters. In our approach, human models and their semantic parameters are correlated as a single linear system of equations. When users input a new set of semantic parameters, a new 3D human body will be synthesized from the exemplar human bodies in the database. This approach involves simpler computation compared to non-linear methods while maintaining quality outputs. A semantic parametric design in interactive speed can be implemented easily. Furthermore, a new method is developed to quickly predict whether the parameter values is reasonable or not, with the training models in the human body database. The reconstructed human bodies in this way will all have the same topology (i.e., mesh connectivity), which facilitates the freeform design automation of human-centric products.

Fast Query for Exemplar-Based Image Completion

Tsz-Ho Kwok, Hoi Sheung, Charlie C.L. Wang
IEEE Transactions on Image Processing, vol.19, no.12, pp.3106-3115, Dec. 2010
[PDF][doi:10.1109/TIP.2010.2052270] [some images]

Abstract:
In this paper, we present a fast algorithm for filling unknown regions in an image using the strategy of exemplar-matching. Unlike the original exemplar-based method using exhaustive search, we decompose exemplars into the frequency coefficients and select fewer coefficients which are the most significant to evaluate the matching score. We have also developed a local gradient-based algorithm to fill the unknown pixels in a query image block. These two techniques bring the ability of input with varied dimensions to the fast query of similar image exemplars. The fast query is based on a search-array data structure, and can be conducted very efficiently. Moreover, the evaluation of search-arrays runs in parallel maps well on the modern graphics hardware with Graphics Processing Units (GPU). The functionality of the approach has been demonstrated by experimental results on real photographs.

Interactive Image Inpainting Using DCT Based Exemplar Matching

Tsz-Ho Kwok, Charlie C.L. Wang
International Symposium on Visual Computing 2009, Part II, LNCS 5876, pp. 709-718. Springer, Heidelberg (2009).
[PDF][doi:10.1007/978-3-642-10520-3_67] [photoshop plugin]
if you meet any problems of using the plugin or find any bugs, please kindly send email to me.

Abstract:
We present a novel algorithm of exemplar-based image in-painting which can achieve an interactive response and generate results with good quality. In this paper, we modify exemplar-based method with the use of Discrete Cosine Transformation (DCT) for the strategy of exemplar matching. We decompose exemplars by DCT and evaluate the matching score with fewer coefficients, which is unprecedented in image inpainting. The reason why using fewer coefficients is so important is that the efficiency of Approximate Nearest Neighbor (ANN) search drops significantly when using high dimensions. We have also developed a local gradient-based filling algorithm to complete the image blocks with unknown pixels so that the ANN search can be adopted to speed up the matching while preserving the continuity of image. Experimental results prove the advantage of this proposed method.

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