Wires: a geometric deformation technique

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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 ...

The Visual Computer, 2007

This paper presents a new, physically based model for performing finite element simulation of deformable objects in which all quantities -strain, stress, displacement, etc. -are computed entirely in local frames of reference. In our framework, subdivision solids with non-homogeneous material properties, such as mass and deformation distributions, can be defined throughout continuous, volumetric domains. This capability enables an animator or virtual sculptor to exert fine-level control over deforming objects and to define a wide variety of physical behaviors. Furthermore, since all quantities pertinent to physical simulation are computed locally, our model facilitates both large-scale and small-scale deformations, as well as rigid or near-rigid transformations. We demonstrate applications of our framework in animation and interactive sculpting and show that interactive simulation of non-trivial, volumetric shapes is possible with our methodologies.

Computers and Graphics, 2010

We introduce WarpCurves, a technique for interactively manipulating an implicit surface using curve-based spatial deformations. Although implicit surfaces have several advantages in 3D modeling, current workflows are limited by the compositional nature of implicit modeling. Wide classes of surface features that are easy to create with the direct manipulation tools available for explicit surface representations are difficult to reproduce using volumetric implicit operations. We describe a novel spatial deformation that can be used to approximate direct surface manipulation. With our method an artist first draws a curve on the current surface to indicate the feature region-of-interest. Deformations applied to this handle curve are transferred to the implicit surface via an automatically-constructed C 2 continuous space mapping. Additional curves can be added in a hierarchical manner to create complex shapes. Our technique is implemented as a node in the BlobTree hierarchical implicit volume representation, and hence can be used along with other volumetric nodes (operators) such as blending and CSG. Our results show that surface deformations which would be difficult to reproduce using existing volumetric operations can be quickly constructed using warp curves, making them a valuable addition to the implicit modeling toolbox.

Computers & Graphics, 2004

Wire curve [15] is a simple, intuitive interface to local deformation of complex geometric objects such as human face models. In this paper, we provide a formulation to extract wire curves and deformation parameters from a facial model based on the displacements of its vertices from those of the corresponding reference model. This extraction process is an inverse process of the wire deformation. With a mild assumption and interactive guide for setting the reference curves and their attributes, we show that the inverse process can be nicely formulated as an over-constrained system of linear equations that can be solved with a least squares minimization technique. We apply the extraction process to multiple face models with different types of expressions to obtain their corresponding wire curves. For facial animation, we blend those extracted wire curves and deformation parameters to finally deform the reference face model. Our proposed scheme facilitates both local deformation and non-uniform blending by making use of the power of wire deformation.

2010

We introduce WarpCurves, a technique for interactively manipulating an implicit surface using curve-based spatial deformations. Although implicit surfaces have several advantages in 3D modeling, current workflows are limited by the compositional nature of implicit modeling. Wide classes of surface features that are easy to create with the direct manipulation tools available for explicit surface representations are difficult to reproduce using volumetric implicit operations.

The Visual Computer, 2007

Haptics on 3D deformable models is a challenge because of the inevitable and expensive 3D deformation computation. In this paper, we propose a new technique that extends the conventional rigid geometry images approach proposed by Gu et al. [9]. Our approach not only flattens the geometry, but also helps to accomplish deformation in an effective and efficient manner. Our approach is suitable for haptics computing, as it performs the deformation on the geometry map itself thereby avoiding the expensive 3D deformation computation. We demonstrate construction of the deformable geometry map representation and its application utilizing practical methods for interactive surgery simulation and interactive textile simulation.

2007

The purpose of visualization is to gain understanding of 3D structures through images. Although many rendering techniques have been proposed for this purpose, the effective visualization remains a challenging task, due to occlusion, clutter, noise in the data, and acquisition pose. Recent solutions to this problem deal with transfer functions and other rendering techniques to enhance the visibility of certain parts of interest. At the core of these techniques is the assumption that the user's role is passive and that the data remains unchanged.

2003

This paper presents a novel Scalar-field based Free-Form Deformation (SFFD) technique founded upon general flow constraints and implicit functions. In contrast to the traditional lattice-based FFD driven by parametric geometry and spline theory, we employ scalar fields as embedding spaces instead. Upon the deformation of the scalar field, the vertices will move accordingly, which result in freeform deformations of the embedded object. The scalar field construction, sketching, and manipulation are both natural and intuitive. By tightly coupling self-adaptive subdivision and mesh optimization with SFFD, versatile multi-resolution free-form deformations can be achieved because our algorithm can adaptively refine and improve the model on the fly to improve the mesh quality. We can also enforce various constraints on embedded models, which enable our technique to preserve the shape features and facilitate more sophisticated design. Our system demonstrates that SFFD is very powerful and intuitive for shape modeling. It significantly enhances traditional FFD techniques and facilitates a larger number of shape deformations.

Symposium on Computer Animation, 2008

DrivenShape is a data-driven technique that exploits known correspondence between two sets of shape deformations (e.g. a character's pose and her shirt). It allows users to drive deformation of secondary object simply by animating the pose shape. The tool is especially useful when the corresponding shapes are highly correlated and the space of all the possible shapes is limited. We have successfully used this technique in our recent productions, and it enabled artists to save on both computation time and man hours.

The Visual Computer, 2004

In this paper, we propose a novel scalar-fieldguided adaptive shape deformation (SFD) technique founded on PDE-based flow constraints and scalar fields of implicit functions. Scalar fields are used as embedding spaces. Upon deformation of the scalar field, a corresponding displacement/velocity field will be generated accordingly, which results in a shape deformation of the embedded object. In our system, the scalar field creation, sketching, and manipulation are both natural and intuitive. The embedded model is further enhanced with self-optimization capability. During the deformation we can also enforce various constraints on embedded models. In addition, this technique can be used to ease the animation design. Our experiments demonstrate that the new SFD technique is powerful, efficient, versatile, and intuitive for shape modeling and animation.

Computer …, 2006

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.

IEEE Transactions on Visualization and Computer Graphics, 2000

Figure 1: Our shape interpolation can interactively provide a dynamic motion between two poses. Here, the interpolation is demonstrated on an elephant model, the first pose being with the trunk down (leftmost) and the final pose (the rest state) being with the trunk up in the air (rightmost). Although many dynamical coefficients can be interactively edited, we show in the top row a direct vibration-free interpolation generated (µ = −1 and η = −1), while the bottom row demonstrates the effect of adding low frequency to the motion: the trunk and ears now dynamically deform throughout the pose interpolation.

Lecture Notes in Computer Science, 2013

This work presents a method to model a spherical mesh by modifying its heightmap in an augmented reality environment. Our contribution is the use of the hierarchical structure of semiregular A4-8 meshes to represent a dynamic deformable mesh suitable for modeling. It defines only a fraction of the overall terrain that is subjected to local deformations. The modeling of spherical terrains is achieved with proper subdivision constraints at the singularities of the parametric space. An error metric dependent on the observer and on the geometry of the topography was used to provide fast visualization and editing. The results demonstrate that the use of the A4-8 mesh combined with the tangible augmented reality system is flexible to shape spherical terrains and can be easily modified to deal with other topologies, such as the torus and the cylinder.

IEEE Computer Graphics and Applications, 2006

C urves are perhaps the most versatile of modeling primitives in computer graphics. They define a rough structure for many surfacegeneration algorithms and are often fit to meaningful surface features for further shape modeling. Deformable objects such as hair and fur are simulated on finite element curve discretizations. Motion paths for planning and animation applications are tied to underlying curves. The internal structure of tubular objects, such as the laces in Figure 1a, are typically built and manipulated using an underlying curve. Artistic strokes for rendering are often defined in terms of an underlying implicit form that follows a curve; Figures 1b and 1c show two real-world examples. Despite this versatility, existing curve models are difficult to work with in applications that require precise control, and where interpenetration with complex objects is objectionable (see Figure 1b). Here, we describe cords, geometric curve primitives designed to appropriately contact geometry while providing a user with precise control.