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.

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.

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.

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.

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.

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.

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.