Measuring the similarity between 3D shapes is a fundamental problem, with applications in computer vision, molecular biology, computer graphics, and a variety of other fields. A challenging aspect of this problem is to find a suitable shape signature that can be constructed and compared quickly, while still discriminating between similar and dissimilar shapes. In this paper, we propose and analyze a method for computing shape signatures for arbitrary (possibly degenerate) 3D polygonal models. The key idea is to represent the signature of an object as a shape distribution sampled from a shape function measuring global geometric properties of an object. The primary motivation for this approach is to reduce the shape matching problem to the comparison of probability distributions, which is a simpler problem than the comparison of 3D surfaces by traditional shape matching methods that require pose registration, feature correspondence, or model fitting. We find that the dissimilarities be...

We present semisimp, a tool for semiautomatic simplification of three dimensional polygonal models. Existing automatic simplification technology is quite mature, but is not sensitive to the heightened importance of distinct semantic model regions such as faces and limbs, nor to simplification constraints imposed by model usage such as animation. semisimp allows users to preserve such regions by intervening in the simplification process. Users can manipulate the order in which basic simplifications are applied to redistribute model detail, improve the simplified models themselves by repositioning vertices with propagation to neighboring levels of detail, and adjust the hierarchical partitioning of the model surface to segment simplification and improve control of reordering and position propagation. ACM Category and Subject Descriptor: I.3.5 [Computer Graphics] Computational Geometry and Object Modeling - hierarchy and geometric transformations Additional Keywords: model simplificatio...

We present a novel aging technique that simulates the deformation of an object caused by repetitive impacts over long periods of time. Our semi-automatic system deteriorates the surface of an object by hitting it with another object. An empirical simulation modifies the object surface to represent the small depressions caused by each impact. This is done by updating the vertices of an adaptively refined object mesh. The simulation is efficient, applying hundreds of impacts in a few seconds. The user controls the simulation through intuitive parameters. Because the simulation is rapid, the user can easily adjust the parameters and see the effect of impacts interactively. The models processed by our system exhibit the cumulative aging effects of repetitive impacts, significantly increasing their realism. Key words: Realism, simulation, aging, deterioration, imperfection, impact, surface, compaction. 1

Introduction It is evident from these course notes and their references that there is a tremendous interest in the general area of simplification of polygonal objects. There are several ways in which one can classify the various simplification techniques. One of these is by examining the nature of the performed simplifications. This section of the course will overview some representative techniques from a hierarchy of increasingly aggressive simplification techniques. In Section 2 we overview a popular approach to compress the connectivity information for polygonal objects -- by using triangle strips. Section 3 overviews Simplification Envelopes and their features. In Section 4 we overview some of our research in simplifying the genus of an object. Constructing a multiresolution hierarchy is only part of the solution in a level-of-detail-based rendering scheme. Switching levels of detail among different objects and at different regions within the same object is

The function representation (FRep) allows for construction of quite complex shapes such as isosurfaces of real-valued functions composed using the functionally defined primitives and operations. Calculating such functions in the complex cases can be very time-consuming. Extraction and visualization of isosurfaces for them can hardly be imagined interactive. In this paper we present a method of an interactive navigation through a "sculpture garden " containing non-intersecting FRep objects defined in the terms of specialized high-level language HyperFun. Before the actual isosurface extraction and visualization occurs, the objects are voxelized on a regular 3D grid with a possibility of a further adaptive voxelization. Polygonization employs a hierarchical representation of the voxelized data and a view-dependent isosurface reconstruction at the different levels of detail. To speedup the extraction process, an isosurface is constructed only in the visible part of the dataset with its updates performed incrementally as observer moves. Due to low preprocessing costs required for isosurface mesh construction, it is possible to visualize timedependent objects, if hardware is capable to calculate updates in real time.

Rendering eciently large virtual environment scenes composed of many elements, dynamic objects, and a highly moving viewpoint is a major issue. This paper focuses on the rst of the two viewing stage operations: required elements determination, the second being shading/ltering. We propose a classication, extending the existing computer graphic techniques toward display scalability requirements, that distinguishes two key points: keeping only required elements (culling), and keeping only required details (which includes traditional LODs). The mechanisms needed for display scalability are presented. Keywords: virtual environment, LOD, intentional display, semantics. 1

Local calculations are used to extend the notion of image-driven polygon mesh simplification. An implementation of the existing image-driven simplification algorithm is presented and it is shown to have the most important features of the original method. A simple technique is developed to evaluate the collapse cost for an edge by generat-ing and considering only image data local to that edge. In addition, the requirement of maintaining images of the original mesh is eliminated. These techniques are combined with the traditional image-driven simplification approach to enable simplification with-out at any point rendering the complete mesh. Benefits of this method include automatic prevention of interior simplification, easier sampling camera definition, and more flex-ibility for future implementations. A technique to reduce texture shifting during mesh simplification, using real-time solid texturing, is also described.

computing in real-time only those parts of the data structure that are immediately necessary to display the model. As the orientation of the model changes with respect to the viewpoint, the data structure will be incrementally computed on-the-y. B. Research Plan 1. Time Estimates for Completion Date Activity 06/2001 Fundamental 3D engine code design and implementation. 10/2001 Literature review and research proposal. 01/2002 Attend DICTA and ACCV Conference. 03/2002 View-dependent LOD implementation. 06/2002 Requirements Specication for Hierarchical Data Structure. 07/2002 Implementation of Hierarchical Data Structure. 08/2002 Performance Evaluation. 09/2002 Engine testing and initial technology demonstration. 12/2002 Adaptive Large-Model Simplication. 05/2003 Thesis Outline. 06/2003 Thesis Composition. 08/2003 Attend SIGGRAPH Conference. 11/2003 Thesis Review. 12/2003 Final Submission. 2. Project Aims Establish a g

An improved method for adaptively constructing a terrain surface representation from a set of data points is presented. Refinement and decimation steps are repeatedly applied to triangular meshes, incrementally determining a better distribution of the data points, while a specified error tolerance is preserved. Even though not asymptotically optimal or monotonically convergent, it produces approximations that are, experimentally, significantly better than those generated by straightforward greedy insertion algorithms.

We present a novel aging technique that simulates the deformation of an object caused by repetitive impacts over long periods of time. Our semi-automatic system deteriorates the surface of an object by hitting it with another object. An empirical simulation modifies the object surface to represent the small depressions caused by each impact. This is done by updating the vertices of an adaptively refined object mesh. The simulation is efficient, applying hundreds of impacts in a few seconds. The user controls the simulation through intuitive parameters. Because the simulation is rapid, the user can easily adjust the parameters and see the effect of impacts interactively. The models processed by our system exhibit the cumulative aging effects of repetitive impacts, significantly increasing their realism.