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GVU Technical Report Series

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Author: Rossignac, Jarek × Author: Shaw, Christopher D. ×

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    Deforming 3D Shapes by Bending and Twisting a Virtual Ribbon with Both Hands
    (Georgia Institute of Technology, 2004) Llamas, Ignacio ; Powell, Alexander ; Rossignac, Jarek ; Shaw, Christopher D.
    Bender is an interactive tool for bending and warping triangulated surfaces. The designer uses a virtual ribbon to grab a portion of the shape and to deform it through direct manipulation. The ribbon is defined by its centerline-a wire made of two smoothly joined circular arcs-and by its twist-the continuous field of normal directions along the wire. The wire and the twist are controlled by a Polhemus tracker in each hand. The deformation model is based on a new formulation of a 3D space warp that uses screw-motions to map coordinate systems aligned with the initial ribbon to corresponding coordinate systems aligned with the final ribbon. Circular biarcs are easy to control and permit the correct handling of situations where a vertex is influenced by different sections of the wire. Screw-motions define smoother and more intuitive warps than other formulations. The combination significantly extends the editing capabilities of previously proposed shape deformation tools and produces smooth and predictable results for configurations where the radius of the tubular region of influence around the ribbon does not exceed the radii of the arcs.
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    Bender: A Virtual Ribbon for Deforming 3D Shapes in Biomedical and Styling Applications
    (Georgia Institute of Technology, 2004) Llamas, Ignacio ; Powell, Alexander ; Rossignac, Jarek ; Shaw, Christopher D.
    In contrast to machined mechanical parts, the 3D shapes encountered in biomedical or styling applications contain many tubular parts, protrusions, engravings, embossings, folds, and smooth bends. It is difficult to design and edit such features using the parameterized operations or even free-form deformations available in CAD or animation systems. The Bender tool proposed here complements previous solutions by allowing a designer holding a 6 DoF 3D tracker in each hand to control the position and orientation of the ends of a stretchable virtual ribbon, which is used to grab the shape in its vicinity and to deform it in realtime, as the designer continues to move, bend, and twist the ribbon. To ensure realtime performance and intuitive control of the ribbon, we model its centerline as a circular biarc and perform adaptive refinement of the triangle-mesh approximation of the surface. To produce a natural and predictable warp, we use the initial and final shapes of the ribbon to define a one-parameter family of screw-motions. The deformation of a surface point is computed by finding its locally closest projection, or projections, on the biarc and by applying the corresponding screws, weighted by a function that decays with the distance to the projection. The combination of these solutions leads to an easy-to-use and effective tool for the direct manipulation of organic or stylized shapes.
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    Finger Sculpting with Digital Clay: 3D Shape Input and Output through a Computer-Controlled Real Surface
    (Georgia Institute of Technology, 2003) Book, Wayne J. ; Glezer, Ari ; Ebert-Uphoff, Imme ; Shaw, Christopher D. ; Rossignac, Jarek ; Allen, Mark G. ; Rosen, David W. ; Askins, Stephen Alexander ; Bai, Jing ; Bosscher, Paul Michael ; Gargus, Joshua ; Kim, Byungmoon ; Llamas, Ignacio ; Nguyen, Austina Nga ; Yuan, Guang ; Zhu, Haihong
    The NSF Digital Clay project is focused on the design, prototyping, integration, and validation of a computer-controlled physical device capable of taking any of a wide range of possible shapes in response to changes in a digital 3D model or to changes in the pressure exercised upon it by human hands. Although it clearly is a natural and unavoidable evolution of 3D graphical user interfaces, its unprecedented capabilities constitute a major leap in technologies and paradigms for 3D display, for 3D input, and for collaborative 3D design. In this paper, we provide an overview of the Digital Clay project and discuss the challenges, design choices, and initial solutions for a new Finger Sculpting interface designed for the Digital Clay and prototyped using conventional 3D I/O hardware.
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    Twister: A Space-Warp Operator for the Two-Handed Editing of 3D Shapes
    (Georgia Institute of Technology, 2003) Llamas, Ignacio ; Kim, Byungmoon ; Gargus, Joshua ; Rossignac, Jarek ; Shaw, Christopher D.
    A free-form deformation that warps a surface or solid may be specified in terms of one or several point-displacement constraints that must be interpolated by the deformation. The Twister approach introduced here, adds the capability to impose an orientation change, adding three rotational constraints, at each displaced point. Furthermore, it solves for a space warp that simultaneously interpolates two sets of such displacement and orientation constraints. With a 6 DoF magnetic tracker in each hand, the user may grab two points on or near the surface of an object and simultaneously drag them to new locations while rotating the trackers to tilt, bend, or twist the shape near the displaced points. Using a new formalism based on a weighted average of screw displacements, Twister computes in realtime a smooth deformation, whose effect decays with distance from the grabbed points, simultaneously interpolating the 12 constraints. It is continuously applied to the shape, providing realtime graphic feedback. The two-hand interface and the resulting deformation are intuitive and hence offer an effective direct manipulation tool for creating or modifying 3D shapes.
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    Finger Sculpting with Digital Clay
    (Georgia Institute of Technology, 2002) Gargus, Joshua ; Kim, Byungmoon ; Rossignac, Jarek ; Shaw, Christopher D.
    "Digital Clay" is a term that signifies a computer-controlled physical surface, capable of taking any of a wide variety of possible shapes in response to changes in a digital 3D model or changes in the pressure exerted upon it by bare hands. The physical properties of such a device impose design and user-interface constraints not encountered in traditional, tracker-based software for the manipulation of virtual models. This paper describes the interaction techniques we have developed to work with this future medium. In particular, we present our solution for tracking the user's fingers using a local deformation of the surface, which we call a "blister", that senses the tangential and normal displacements of the finger. We also present a solution for creating variable-height bosses and creases with the simple sweep of a finger. Since the Digital Clay hardware is not yet operational, we have implemented a haptic simulation framework based on a PHANTOM device.