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LinearDragger: a Linear Selector for One-finger Target Acquisition
Oscar Kin-Chung Au, Xiaojun Su, Rynson W.H. Lau
ACM CHI Conference on Human Factors in Computing Systems 2014

[project page][pdf]


Abstract: Touch input is increasingly popular nowadays, especially for mobile devices such as smartphones and tablet computers. However, the human finger has considerably large fingertip size and finger input is imprecise. As such, acquiring small targets on a touch screen is still a challenging task. In this paper, we present the LinearDragger, a new and integrated one-finger target acquisition technique for small and clustered targets. The proposed method has three advantages. First, it allows users to select targets in dense clustered groups easily with a single touch-drag-release operation. Second, it maps the 2D selection problem into a more precise 1D selection problem, which is independent of the target distribution. Third, it avoids finger occlusion and does not create visual distraction. As a result, it is particularly suitable for applications with dense targets and rich visual elements. Results of our controlled experiments show that when selecting small targets, LinearDragger takes about 70% and 30% less selection time than target acquisition without using any techniques and with the state-of-the-art target acquisition technique that involves a single touch operation, respectively, while maintaining a reasonable error rate.
The Implicit Fan Cursor: A Velocity Dependent Area Cursor
Xiaojun Su, Oscar Kin-Chung Au, Rynson W.H. Lau
ACM CHI Conference on Human Factors in Computing Systems 2014
[project page] [pdf] [Demo program]


Abstract: We present the Implicit Fan Cursor (IFC) – a novel target pointing technique using a cursor with a fan-shape activation area. The IFC couples the cursor’s activation area with its velocity, i.e., the speed and direction of the mouse motion, behaving like a 2D spotlight cursor at low speed and a circular area cursor at high speed. Thus, it enables the user to precisely acquire distant targets at low speed and easily acquire nearest targets at high speed, without explicit mode switch- ing. This technique minimizes cursor movement, while taking into consideration of the precision of cursor movement at different speeds. It also ensures that only one target is captured at any time. The results of our controlled experiments show that the IFC outperforms the point cursor and the area cursor techniques, particularly in terms of cursor moving distance, and that its performance can be accurately modeled using the Fitts’ law.
Journal Papers
A Handle-Independent Reduced Model for Incremental Mesh Editing
Yirui Wu, Oscar Kin-Chung Au, Chiew-Lan Tai, Tong Lu
Computer Aided Geometric Design, Volumes 35–36, May 2015, Pages 56–68, special issue for Geometric Modeling and Processing 2015.
Abstract: Most existing handle-based mesh deformation methods require costly re-computation for every handle set updating, namely, adding or removing of handles on the mesh surface. In this paper, we propose a reduced deformation model that is independent of handle configuration, allowing users to dynamically update the handle set without noticeable waiting time. We represent the deformation space of a mesh as propagation fields defined by only the mesh geometry, independent of the handle set. We define the propagation fields as selected eigenvectors of the Laplacian operator and adopt the transformations of isolines sampled from the fields as the deformation descriptors. In this way, the deformation descriptors are pre-computed before handle specification. During interactive manipulation, constraints generated from the handles are incorporated into the deformation system in real time. Our method therefore supports incremental mesh editing where the user can freely define different handle sets to edit different parts of the shape without waiting for long re-computation. Our reduced model is scalable since the updating time per iteration is independent of the mesh size and the number of handles. We demonstrate the effectiveness of the proposed deformation method and compare its performance with related reduced deformation models.
Spectral 3D mesh segmentation with a novel single segmentation field
Hao Wang, Tong Lu, Oscar Kin-Chung Au, Chiew-Lan Tai
Graphical Models, 76(5), 440 - 456, 2014
Abstract: We present an automatic mesh segmentation framework that achieves 3D segmentation in two stages, hierarchical spectral analysis and isoline-based boundary detection. During the hierarchical spectral analysis stage, a novel segmentation field is defined to capture a concavity-aware decomposition of eigenvectors from a concavity-aware Laplacian. Specifically, a sufficient number of eigenvectors is first adaptively selected and simultaneously partitioned into sub-eigenvectors through spectral clustering. Next, on the sub-eigenvectors level, we evaluate the confidence of identifying a spectral-sensitive mesh boundary for each sub-eigenvector by two joint measures, namely, inner variations and part oscillations. The selection and combination of sub-eigenvectors are thereby formulated as an optimization problem to generate a single segmentation field. In the isoline-based boundary detection stage, the segmentation boundaries are recognized by a divide-merge algorithm and a cut score, which respectively filters and measures desirable isolines from the concise single segmentation field. Experimental results on the Princeton Segmentation Benchmark and a number of other complex meshes demonstrate the effectiveness of the proposed method, which is comparable to recent state-of-the-art algorithms.
Two-Finger Gestures for 6DOF Manipulation of 3D Objects
Jingbo Liu, Oscar Kin-Chung Au, Hongbo Fu, Chiew-Lan Tai
Computer Graphics Forum (CGF): special issue of Pacific Graphics 2012.
[project page][pdf]
Abstract: Multitouch input devices afford effective solutions for 6DOF (six Degrees of Freedom) manipulation of 3D objects. Mainly focusing on large-size multitouch screens, existing solutions typically require at least three fingers and bimanual interaction for full 6DOF manipulation. However, single-hand, two-finger operations are preferred especially for portable multitouch devices (e.g., popular smartphones) to cause less hand occlusion and relieve the other hand for necessary tasks like holding the devices. Our key idea for full 6DOF control using only two contact fingers is to introduce two manipulation modes and two corresponding gestures by examining the moving characteristics of the two fingers, instead of the number of fingers or the directness of individual fingers as done in previous works. We solve the resulting binary classification problem using a learning-based approach. Our pilot experiment shows that with only two contact fingers and typically unimanual interaction, our technique is comparable to or even better than the state-of-the-art techniques.

Lazy Selection: A Scribble-based Tool
for Smart Shape Elements Selection
Pengfei Xu, Hongbo Fu, Oscar Kin-Chung Au, Chiew-Lan Tai
ACM Transaction on Graphics (Proceedings of SIGGRAPH Asia 2012)
[project page] [pdf]
Abstract: This paper presents Lazy Selection, a scribble-based tool for quick selection of one or more desired shape elements by roughly stroking through the elements. Our algorithm automatically refines the selection and reveals the user's intention. To give the user maximum flexibility but least ambiguity, our technique first extracts selection candidates from the scribble-covered elements by examining the underlying patterns and then ranks them based on their location and shape with respect to the user-sketched scribble. Such a design makes our tool tolerant to imprecise input systems and applicable to touch systems without suffering from the fat finger problem. A preliminary evaluation shows that compared to the standard click and lasso selection tools, which are the most commonly used, our technique provides significant improvements in efficiency and flexibility for many selection scenarios.

Multitouch Gestures for Constrained Transformation of 3D Objects
Oscar Kin-Chung Au, Chiew-Lan Tai, Hongbo Fu
Computer Graphics Forum (CGF): special issue of Eurographics 2012. 31(2): 651 - 660.
[project page] [pdf]
PCT Application No. PCT/CN2012/000150
Abstract: 3D transformation widgets allow constrained manipulations of 3D objects and are commonly used in many 3D applications for fine-grained manipulations. Since traditional transformation widgets have been mainly designed for mouse-based systems, they are not user friendly for multitouch screens. There is little research on how to use the extra input bandwidth of multitouch screens to ease constrained transformation of 3D objects. This paper presents a small set of multitouch gestures which offers a seamless control of manipulation constraints (i.e., axis or plane) and modes (i.e., translation, rotation or scaling). Our technique does not require any complex manip- ulation widgets but candidate axes, which are for visualization rather than direct manipulation. Such design not only minimizes visual clutter but also tolerates imprecise touch-based inputs. To further expand our axis-based interaction vocabulary, we introduce intuitive touch gestures for relative manipulations, including snapping and borrowing axes of another object. A preliminary evaluation shows that our technique is more effective than a direct adaption of standard transformation widgets to the tactile paradigm.

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Mesh Segmentation with Concavity-aware Fields
Oscar Kin-Chung Au, Youyi Zheng, Menglin Chen, Pengfei Xu, Chiew-Lan Tai
IEEE Transactions on Visualization and Computer Graphics. 18(7): 1125 - 1134.
[project page] [pdf]
Abstract: This paper presents a simple and efficient automatic mesh segmentation algorithm that solely exploits the shape concavity information. The method locates concave creases and seams using a set of concavity-sensitive scalar fields. These fields are computed by solving a Laplacian system with a novel concavity-sensitive weighting scheme. Isolines sampled from the concavity-aware fields naturally gather at concave seams, serving as good cutting boundary candidates. In addition, the fields provide sufficient information allowing efficient evaluation of the candidate cuts. We perform a summarization of all field gradient magnitudes to define a score for each isoline and employ a score-based greedy algorithm to select the best cuts. Extensive experiments and quantitative analysis have shown that the quality of our segmentations are better than or comparable with existing state-of-the-art more complex approaches.

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Dot Scissor: A Single-Click Interface for Mesh Segmentation
Youyi Zheng, Chiew-Lan Tai, Oscar Kin-Chung Au
IEEE Transactions on Visualization and Computer Graphics. 18(8), 1304 - 1312.
[project page] [pdf]
Abstract: This paper presents a very easy-to-use interactive tool, which we call dot scissor, for mesh segmentation. The user's effort is reduced to placing only a single click where a cut is desired. Such a simple interface is made possible by a directional search strategy supported by a concavity-aware harmonic field and a robust voting scheme that selects the best isoline as the cut. With a concavity-aware weighting scheme, the harmonic fields gather dense isolines along concave regions which are natural boundaries of semantic components. The voting scheme relies on an isoline-face scoring mechanism that considers both shape geometry and user intent. We show by extensive experiments and quantitative analysis that our tool advances the state-of-the-art segmentation methods in both simplicity of use and segmentation quality.

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Bilateral Normal Filtering for Mesh Denoising
Youyi Zheng, Hongbo Fu, Oscar Kin-Chung Au, and Chiew-Lan Tai
IEEE Transactions on Visualization and Computer Graphics (TVCG). 17(10): 1521-1530, 2010.
Abstract: Decoupling local geometric features from the spatial location of a mesh is crucial for feature-preserving mesh denoising. This paper focuses on first-order features, i.e., facet normals, and presents a simple yet effective anisotropic mesh denoising framework via normal field denoising. Unlike previous denoising methods based on normal filtering, which process normals defined on the Gauss sphere, our method considers normals as a surface signal defined over the original mesh. This allows the design of a novel bilateral normal filter that depends on both spatial distance and signal distance. Our bilateral filter is a more natural extension of the elegant bilateral filter for image denoising than those used in previous bilateral mesh denoising methods. Besides applying this bilateral normal filter in a local, iterative scheme, as common in most of previous works, we present for the first time a global, non-iterative scheme for anisotropic denoising. We show that the former scheme is faster and more effective for denoising extremely noisy meshes while the latter scheme is more robust to irregular surface sampling. We demonstrate that both our feature-preserving schemes generally produce visually and numerically better denoising results than previous methods, especially at challenging regions with sharp features or irregular sampling.

Component-wise Controllers for Structure-preserving Shape Manipulation
Youyi Zheng, Hongbo Fu, Daniel Cohen-Or, Oscar Kin-Chung Au, and Chiew-Lan Tai
Computer Graphics Forum (CGF): special issue of Eurographics 2011. 30(2): 563-572, 2011.
[project page] [pdf]
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Abstract: Recent shape editing techniques, especially for man-made models, have gradually shifted focus from maintaining local, low-level geometric features to preserving structural, high-level characteristics like symmetry and parallelism. Such new editing goals typically require a pre-processing shape analysis step to enable subsequent shape editing. Observing that most editing of shapes involves manipulating their constituent components, we introduce component-wise controllers that are adapted to the component characteristics inferred by shape analysis. The controllers capture the natural degrees of freedom of individual components and thus provide an intuitive user interface for editing. A typical model often results in a moderate number of controllers, allowing easy establishment of semantic relations among them by automatic shape analysis supplemented with user interaction. We propose a component-wise propagation algorithm to automatically preserve the established inter-relations while maintaining the defining characteristics of individual controllers and respecting the user-specified modeling constraints. We extend these ideas to a hierarchical setup, allowing the user to adjust the tool complexity with respect to the desired modeling complexity. We demonstrate the effectiveness of our technique on a wide range of engineering models with structural features, often containing multiple connected pieces.

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Rapid Detection of Apoptosis in Mammalian Cells by Using Intact Cell MALDI Mass Spectrometry [pdf]
Hongjuan Dong, Wei Shen, Myra Ting Wai Cheung, Yimin Liang, Hon Yeung Cheung, Günter Allmaier, Oscar Kin-Chung Au, Yun Wah Lam
Analyst, 2011, 136: 5181 - 5189.
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Electors Voting for Fast Automatic Shape Correspondence [project page] [pdf]
Oscar Kin-Chung Au, Chiew-Lan Tai, Daniel Cohen-Or, Youyi Zheng, and Hongbo Fu
Computer Graphics Forum (CGF): special issue of Eurographics 2010
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Skeleton Extraction by Mesh Contraction [project page] [pdf]
Oscar Kin-Chung Au, Chiew-Lan Tai, Hung-Kuo Chu, Daniel Cohen-Or, Tong-Yee Lee
ACM Transactions on Graphics (TOG) Volume 27 , Issue 3 (August 2008) Proceedings of ACM SIGGRAPH 2008
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Handle-Aware Isolines for Scalable Shape Editing [project page] [pdf]
Oscar Kin-Chung Au, Hongbo Fu, Chiew-Lan Tai, Daniel Cohen-Or
ACM Transactions on Graphics (TOG) Volume 26 , Issue 3 (July 2007) Proceedings of ACM SIGGRAPH 2007
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Dual Laplacian Editing for Meshes [project page] [pdf]
Oscar Kin-Chung Au, Chiew-Lan Tai, Ligang Liu, Hongbo Fu
IEEE Transactions on Visualization and Computer Graphics. 12(3): 386-395, MAY/JUNE 2006.
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Effective Derivation of SimilarityTransformations for Implicit Laplacian Mesh Editing [project page] [pdf]
Hongbo Fu, Oscar Kin-Chung Au, Chiew-Lan Tai
Computer Graphics Forum. 26(1): 34 - 45, March 2007.
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Sampling-sensitive Multiresolution Hierarchy for Irregular Meshes [pdf]
Oscar Kin-Chung Au, Chiew-Lan Tai
Visual Computer. 20(7): 479 - 493, September, 2004.
Conference Papers
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Cultural Data Sculpting: Omnispatial Visualization for Cultural Datasets [link]
Sarah Kenderdine, Oscar Kin Chung Au, Jeffrey Shaw
Information Visualisation (IV), 2011 15th International Conference on, July 13-15, 2011, London, UK, IEEE Press.
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Multitouch Finger Registration and Its Applications [project page] [pdf]
Oscar Kin-Chung Au, and Chiew-Lan Tai
Proceedings of the 22nd Conference of the Computer-Human Interaction Special Interest Group of Australia on Computer-Human Interaction (OZCHI 2010), November 22-26, 2010, Brisbane, Australia, ACM Press.
U.S. Patent Application No. 13/328,549
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Optimal Boundaries for Poisson Mesh Merging [pdf]
Xiaohuang Huang, Hongbo Fu, Oscar Kin-Chung Au, Chiew-Lan Tai
ACM Solid and Physical Modeling Symposium 2007 (SPM 2007).
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Morphing with Laplacian Coordinates and Spatial-temporal Texture [pdf]
Hongbo Fu, Chiew-Lan Tai, Oscar Kin-Chung Au
Pacific Graphics 2005.
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Mesh Editing with Curvature flow Laplacian [pdf]
Oscar Kin-Chung Au, Chiew-Lan Tai, Hongbo Fu, Ligang Liu
Symposium of Geometry Processing, Vienna, 4-6 July, 2005 (poster).