Finding effective interactive deformation techniques for complex geometric objects continues to be a challenging problem in modeling and animation. We present an approach that is inspired by armatures used by sculptors, in which wire curves give definition to an object and shape its deformable features. We also introduce domain curves that define the domain of deformation about an object. A wire together with a collection of domain curves provide a new basis for an implicit modeling primitive. Wires directly reflect object geometry, and as such they provide a coarse geometric representation of an object that can be created through sketching. Furthermore, the aggregate deformation from several wires is easy to define. We show that a single wire is an appealing direct manipulation deformation technique; we demonstrate that the combination of wires and domain curves provide a new way to outline the shape of an implicit volume in space; and we describe techniques for the aggregation of deformations resulting from multiple wires, domain curves and their interaction with each other and other deformation techniques. The power of our approach is illustrated using applications of animating figures with flexible articulations, modeling wrinkled surfaces and stitching geometry together.

We present a new particle-based surface representation with which a user can interactively sculpt free-form surfaces. The particles maintain mesh connectivity and operate under rules that lead them to form triangulations with properties that make them suitable for use in subdivision. A user interactively guides the particles, which we call skin, to grow over a given collection of polyhedral elements (or skeletons), yielding a smooth surface (through subdivision) that approximates the underlying skeletal shapes. Skin resembles blobby modeling in the constructive approach to modeling it supports, but allows a richer vocabulary of skeleton shapes, supports sharp creases where desired, and provides a convenient mechanism for adding multiresolution surface detail. CR Categories and Subject Descriptors: I.3.5 [Computer Graphics ]: Computational Geometry and Object Modeling I.3.6 [Computer Graphics]: Methodology and Techniques Additional Key Words: Free-form modeling, meshes, subdivision, m...

Sphere tracing is a new technique for rendering implicit surfaces using geometric distance. Distance-based models are common in computer-aided geometric design and in the modeling of articulated figures. Given a function returning the distance to an object, sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. Sphere tracing is particularly adept at rendering pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Current root finding techniques such as L-G surfaces and interval analysis require periodic evaluation of the derivative, and their behavior is dependent on the behavior of the derivative. Sphere tracing requires only a bound on the magnitude of the derivative, robustly avoiding problems Manuscript, July 1994. Recommended for publication: The Visual Computer. 5-70 where the derivative jumps or vanishes. This robustness and scope ...

We propose an algorithm for creating novel views of a non-rigidly varying dynamic event by combining images captured from different positions, at different times. The algorithm operates by combining images captured across space and time to compute voxel models of the scene shape at each time instant, and dense 3D scene flow between the voxel models (the non-rigid motion of every point in the scene). To interpolate in time the voxel models are “flowed ” using the appropriate scene flow and a smooth surface fit to the result. The novel image is then computed by ray-casting to the surface at the intermediate time, following the scene flow to the neighboring time instants, projecting into the input images at those times, and finally blending the results. We use the algorithm to create re-timed slow-motion fly-by

: We introduce a method for the construction of skeletal curves from an unorganized collection of scattered data points lying on a surface. These curves may have a tree like structure to capture branching shapes such as blood vessels. The skeletal curves can be used for different applications ranging from surface reconstruction to object recognition. As an input, the algorithm takes a set of 3D points. It returns a set of curves arranged in a tree structure. The only interaction needed is the selection of a data point which represent the root of the tree. A neighborhood graph is constructed over the set of points to compute geodesic distances between the root point and the other points. Connected level sets of the distance map are then extracted and organized in a tree structure. The centers of these levels sets constitute the skeletal curves. Key-words: visualization, skeletal curve, cylindrical decomposition, generalized cylinders, reconstruction (R'esum'e : tsvp) Anne.Verroust@in...

This paper presents a new method that combines a incdial axis and implicit sub,faces in order to reconstruct a 3D solid from an unstructured set of points scattered on the objcct's sufacc. The representation produced is based on iso-sufaccs generated by skeletons, and is a particularly compact way of defining a smooth free-form solid. The method is based on the minimisation of an energy representing a "distance" between the set of data points and the iso-sufacc, resembling previous rcscrach 9. Initialisation, however, is more robust and ej]ficicnt since there is computation of the incdial axis of the set of points. Instead of subdividing existing skeletons in order to refine the objcct's sufacc, a new reconstruction algorithm progressively selects skeleton-points from the prccomputed incdial axis using an heuristic principle based on a "local energy" criterion. This drastically speeds up the reconstruction process. Moreover, using the incdial axis allows reconstruction of objects with complex topology and geometry, like objects that have holes and branches or that arc composed of several connected components. This process is fully automatic. The method has bccn successfully applied to both synthetic and real data.

The implicit surface modelling technique can be used to model "soft" objects, objects whose surface or topology changes over time. It offers the opportunity of modelling and animating relatively complex shapes using only a few primitives. The final object is constructed by blending the primitives, and as the primitives are moved the blended surface changes shape. This can cause problems with object appearance and consistency and unwanted blending of object parts. In this paper we describe work in progress which addresses these problems. 1. Introduction Implicit surfaces are often overlooked in computer graphics and animation because other techniques such as polygonal or parametric surfaces offer more established ways of visualising modelled objects. On the other hand objects being modelled often change their shape over time. The piece-wise nature of polygonal or parametric surfaces imposes the need for tedious polygon or patch fitting to maintain surface continuity and smooth blendin...

This paper presents a new adaptive sampling method for implicit surfaces that can been used in both interactive modeling and animation. The algorithm samples implicit objects generated by skeletons and e#ciently maintains this sampling, even when their topology changes over time such as during fractures and fusions. It provides two complementary modes of immediate visualization: displaying "scales" lying on the surface, or a piecewise polygonization. The sampling method is particularly well suited to e#ciently avoid "unwanted blending" between di#erent parts of an object.

This paper presents a hybrid method for creating three-dimensional shapes by sketching silhouette curves. Given a silhouette curve, we approximate its medial axis as a set of line segments, and convolve a linearly weighted kernel along each segment. By summing the fields of all segments, an analytical convolution surface is obtained. The resulting generic shape has circular cross-section, but can be conveniently modified via sketched profile or shape parameters of a spatial transform. New components can be similarly designed by sketching on different projection planes. The convolution surface model lends itself to smooth merging between the overlapping components. Our method overcomes several limitations of previous sketched-based systems, including designing objects of arbitrary genus, objects with semi-sharp features, and the ability to easily generate variants of shapes.

Implicit surfaces obtainedbyconvolution of multi-dimensional primitives with some potential function, are a generalisationofpopular implicit surface models: blobs, metaballs and soft objects. These models di er in their choice ofpotential functions but agree upon the use of underlying modelling primitives, namely, points. In this paper a method is described formodelling and rendering implicit surfaces built upon an expanded set of skeletal primitives: points, line segments, polygons, arcs and planes. An algorithm for ray-tracing the surfaces formed through convolution of any combination of these primitives is also presented. The algorithm employs analytical methods only, which makes it computationally e ective.